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    Mono-flo or Parallel piping is small home? (71 Posts)

  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 10:49 AM
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    Direct Return or Reverse Return in a small home?

    I'm installing a radiant system in my 1,500 sq ft home in the SF Bay Area (moderate climate). The home is very well insulated. I've decided on Runtal radiators and in speaking with the Runtal rep he told me that a parallel piping system would be better than a monoflo system. His reasoning makes perfect sense: in a mono-flow system the water continues to lose heat as in passes through the radiators and that the last radiator will run less efficiently that the first. It also makes sense that in a parallel piping system the water temp is consistent through all radiators. Do you agree/disagree?

    I'm attaching a zone diagram that I designed that has what I believe is a parallel piping system for one of the 2 zones planned for my home. Does it make any sense? Am I doing this correctly? I want to have flow control valves at each radiator to allow heat adjustment for the individual rooms. Comments appreciated. I'm a remodeling contractor but have limited knowledge of hydronics. Looking for help with the design and install, was told this was the right place for both. thcx
    This post was edited by an admin on October 17, 2013 11:09 AM.
  • RJ RJ @ 12:27 PM
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     Direct return      Make sure you install positive shut off valves on supply and return on each radiator as well as your balancing valve and drain and purge valves or air vents at high points,  these valves will help you when filling and draining system.  some prefer balancing valves on the return of the radiator,  ball valves not recommended for balancing, use a good quality balance valve that has gauge ports for installing a balance meter or gauges.   Bell&Gosset, Taco or Victaulic make good valves
  • SWEI SWEI @ 12:58 PM
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    Reverse Return

    would be best if the layout permits.

    Panel radiators are usually sold with fittings that include multi-turn stops  (for balancing) and unions.

    TRVs would add another level of both comfort and control.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 1:18 PM
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    What is a "reverse return"?

    1). What is a "reverse return"?

    2). I'm using Runtal radiators which do not have built in valves on wall panels. My supply will be coming in through an exterior wall so I had planned to use an angle valve to control water flow to each radiator.

    Comments welcomed...thanks! I'm an idiot but getting slowly smarter with help from you guys :)
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 1:57 PM
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    Reverse Return

    OK, I found an example diagram of "reverse return". Is this diagram correct?

    What is the advantage of a reverse return vs what I show in my original diagram? Not sure reverse return is practical since the last radiator in the loop is farthest away from the boiler and I'd need a lengthy run to return to the radiator. My original diagram looks to be more efficient from a total pipe required perspective.
    This post was edited by an admin on October 15, 2013 2:00 PM.
  • SWEI SWEI @ 2:19 PM
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    Reverse Return

    Will push roughly the same amount of water through each branch without a lot of throttling required, and tends to maintain the system balance even when zones are turned on and off.  It's not required, but it makes balancing the system much easier.

    Have you considered piping as a single zone, with TRVs on each radiator?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 1:03 PM
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    why 2 shutoff valves at each radiator?

    Thanks for the reply. I'm a neophyte trying to learn on the fly....not an ideal situation but I can't afford to hire an hydronics pro so I'm committed to learning.

    I understand about the air gap valves at the high points, makes sense to clear the line of air when filling/refilling, but I don't understand why I'd want shut off valves at both supply and return on individual radiators. I thought the purpose of a shutoff valve on individual radiators was to control the amount of heat output for each radiator. Is this correct? Why would 2 shutoffs be required on each radiator, one each at supply and return?
  • RJ RJ @ 1:21 PM
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    shut off valves will allow isolation of individual radiators for any future repairs,  proper piping practice used by steamfitters for decades,  some balancing valves,circut setters are not 100% shutoff.   I worked in the Bay Area for 20 yrs,  If you dont already have a contractor call RMA   Redwood Mechanical or ABCO Mechanical
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 1:39 PM
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    Thanks for the reply. I can't afford to hire a contractor, although I do know a heating contractor willing to consult for a fee....I'm setting that up now. I've been in the trades for years, I've sweated miles of copper and am confident I can assemble the system. It's the piping layout, valve positioning, radiator positioning I need help with. I had one guy tell me it was a waste to put radiators on interior walls and that it's better to put a single large radiator on one outside wall to heat a great room rather than use several radiators positioned around interior walls. It's that type of counter-intuitive info I'm having trouble understanding. I've purchased the Dan Holohan book on radiant heat but found it useless as it's geared toward in-floor heating. I haven't yet found a good basic primer on wall/baseboard radiant heating.
  • Zman Zman @ 3:02 PM
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    Home Run

    Panel radiators will work well in reverse return as suggested. The idea setup is to run a supply and return from each panel back to the mechanical area. These lines would likely be 1/2". This is true parallel piping. From there you can control and balance it and way you please. I like TRV's because it gives great local control.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 3:12 PM
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    reverse return

    Frankly I don't see the advantage of what you refer to as "reverse return" over what I'm showing in my original red and blue diagram. I do see a big disadvantage in the reverse return scheme in my layout because it would result in an additional lengthy pipe from the last radiator back to the boiler. Could you explain how the "reverse return" is better than the scheme I diagramed, and why you believe it is worth the extra 75' of return piping?
  • SWEI SWEI @ 3:34 PM
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    Direct Return

    Water is lazy, to quote our esteemed host.  Direct return piping creates a "shortest route" for the water to take through the first radiator in the string.  It's harder to push water through each successive radiator as you get further from the boiler.  This can be countered by throttling down the balancing valves on the first radiator, less on the next, and so on.  If the flow changes from a variable speed pump, or a zone valve closing, the system balance will change, with different ratios now flowing through each branch in the system. explains this in some detail.

    If you put TRVs on each radiator (in effect turning each into its own zone) the piping becomes less critical, since the TRVs will throttle up and down in to maintain temperature.  A manifold system is sometimes easier to install, but often a hybrid branch and loop system makes a better fit.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 10:49 AM
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    TRV's and reverse return questions

    Thanks to all for the informative responses. I want to make sure understand 2 of the concepts mentioned:

    Reverse Return: The head pressure created in the reverse return drain line actually strengthens the input flow of hot water to upstream radiators. Is this correct?

    Thermostatic Radiator Valves: automatically adjust the input flow to individual radiators to control the temp in each room. Is this correct?

    It was suggested that if TRV's are used then a reverse return isn't needed. Is this a misunderstanding? Or, is it better to use both a reverse return layout AND TRVs?

    One concern I have is that with a reverse return system, you are asking the pump to push a higher volume of water due to the added length of piping required. How does this effect efficiency?
    This post was edited by an admin on October 16, 2013 11:16 AM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 3:00 PM
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    Is this a correctly drawn Reverse Return diagram?

    I've revised my drawing to what I believe is a Reverse Return system. Does this look correct? Is anything missing/incorrectly drawn?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 10:22 PM
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  • SWEI SWEI @ 3:00 AM
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    Diagram looks good

    Though if the house is anything approaching rectangular, your original drawing offers a shorter route. 
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 10:58 AM
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    diagram looks good

    "Though if the house is anything approaching rectangular, your original drawing offers a shorter route."

    Yes but didn't we agree that a reverse return solution was better for balancing than the direct return shown in the original drawing? I'm do I achieve a "short route" similar to that in the first drawing, but using a reverse return system? The 'longer route" in the reverse return drawing is due to the length return of the boiler return back to the boiler room. I'm open to suggestions on how to solve this...thanks.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 11:58 AM
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    Balancing a reverse return system

    I've read several web articles that say line balancing is critical to a successful reverse return system. If I understood correctly, they were saying that a balanced system is one in which the boiler input line is approximately the same length as the boiler return line. The problem I'm having with my design is that my last radiator ends some distance from the boiler, causing the boiler return line to extend much longer than the boiler input line. Seems to me in an ideal reverse return system, the First radiator and the Last radiator will be approximately the same distance from the boiler, thereby allowing both input and return lines to be equal in length. Am I thinking correctly? The only way I can achieve this on my house is a single zone that begins at a radiator located about 10 feet from the boiler and ends at a radiator also about 10 feet from the boiler. This would allow both input and returns of the same length, hence a balanced system. Is this correct thinking?
    This post was edited by an admin on October 17, 2013 11:59 AM.
  • SWEI SWEI @ 2:55 PM
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    Sorry, second drawing

    not original drawing.

    A difference in supply and return line lengths prior to the first branch on each is not important, as long as the trunk lines are the right size.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 3:30 PM
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    Need clarification

    "A difference in supply and return line lengths prior to the first branch on each is not important, as long as the trunk lines are the right size."

    That statement confused me. In a reverse return there is only a supply line prior to the first branch (radiator), correct? And, the return pipe begins at the outflow of the first radiator. In your statement you refer to a return line prior to the first branch. I don't understand.

    My balance questioned referred to the lengthy return line that exits the last radiator then makes a long solo run back to the radiator (re-attaching my drawing for clarify). Does this represent an imbalanced system?
    This post was edited by an admin on October 17, 2013 3:31 PM.
  • SWEI SWEI @ 6:36 PM
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    Supply lines

    meaning the fat red and blue lines in the above diagram.  The difference in length you describe is not an issue, as long as the lines are large enough to carry the volume you need without adding too much head to the system.  If they maintain the same diameter through their entire length (not reduced as they get to the end of the line) then it's really just length and diameter.

    As mentioned above and also in the other thread you started, TRVs will reduce the usefulness of reverse return piping.  If you use them, you also won't need two zones.
    This post was edited by an admin on October 17, 2013 6:42 PM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 6:46 PM
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    Reverse Return Balance

    Thank you for the response.

    I've read in several publications that in order to maintain system balance (without introducing balance valves) that the input and return lines must be the same length. In my drawing, the return line is substantially longer than the input line. This seems at odds with your comment. Could you clarify? Thank you.
  • SWEI SWEI @ 7:13 PM
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    Input and return lines do NOT have to be the same length

    the goal is to have the total trip (supply -> emitter -> return) the same length for each emitter.  The difference between the lengths of the supply and return pipes between the heat source and the first branch is immaterial.
  • Gordy Gordy @ 7:10 PM
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    How reverse return can benefit a TRVed system. Because I'm not seeing an advantage worth the labor, and materials.
  • SWEI SWEI @ 7:14 PM
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    I don't believe I said that

    or did I miss something?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 7:19 PM
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    "The difference in length you describe is not an issue"

    I interpreted that as meaning a difference in lengths between supply and return pipes would not affect system balance. This is a key point I've been struggling to understand. I'm hoping you could provide some more explanation to fill in my knowledge gaps....and there are plenty :).

    I greatly appreciate your help.
  • Gordy Gordy @ 7:19 PM
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    Not saying you did trying to put two threads together here. But I see the OPs drawing is using TRVs, and he's trying to implement reverse return in the same drawing. Maybe I missed something Kurt?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 7:38 PM
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    time to reset the conversation

    First off, I'm experienced in the area of hydronic heating so any confusion falls at my feet.

    I'm attempting to design a simple system to heat my small home. Here's what I've concluded from various articles I've read the last several days:

    1) One pipe series system is not desirable due to the pressure and heat loss as the unput travels through the radiators.

    2) A 2 pipe direct return system is better, but is prone to system imbalance due to the "path of least resistance" effect of the return piping. This effect can be somewhat minimized with the use of TRV's.

    3) A 2 pipe reverse return system avoids the "path of least resistance" problem of a direct return system and thus is an inherently more balance system than either of the above choices. Optimal balance is achieved in a reverse return system when the input and return piping are about the same length. To some extent, pressure imbalance in a reverse return system can be offset with TRV's on each radiator in the system.

    Does this make sense so far?

    I've decided on designing a reverse return system to optimize pressure balance, and am adding TRV's not specifically to balance the system but to maintain a desired temperature in each room where a radiator is located.

    So now there is still an unanswered question with respect to the piping lengths in a reverse return system. As I mentioned, I've read in a few articles that optimal balance is achieved in a reverse return system when the input and return piping is the same length. In my latest design, the return pipe is nearly double the length of the input pipe. This is because my last radiator in the system is far away from the boiler, necessitating the lengthy return pipe length. So 2 questions here really: 1) does the long return piping diminish system pressure balance as I've read it does? and 2) does it really matter if I'm using TRV's on every radiator?
    This post was edited by an admin on October 17, 2013 7:38 PM.
  • Gordy Gordy @ 7:58 PM
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    The idea is

    To have the same distance traveled from the supply of the boiler to the return of the boiler in each rung of the ladder.

    Soon the first closest radiators supply water will be the last to return to the boiler. That's where the reverse comes in. But this is only going to give balance of each circuit has close to the same resistance.

    I would use the TRVs and call it good. How often will all heating loops call for heat, and for the same length of time. TRVs will be throttling demand on each loop. How drastic are the heat loss differences in each zone?
  • hot rod hot rod @ 9:43 PM
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    Home run piping?

    Is that an option? Delta p circ
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 10:09 PM
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    Home Run Piping is not an option choice.
  • RobG RobG @ 1:04 PM
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    An easier way

    An easier way to do the reverse return piping would be to start at boilers supply and connect to BR1 then BR2 then MasterBR and end at Office. that way you avoid looping all the way back around the systerm. hope this helps.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 1:15 PM
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    response to "an easier way"

    If I did as you suggest yes it would shorten the lengthy return pipe, but it would also nearly double the input pipe length so no improvement in balance really....unless i missed something?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 1:27 PM
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    I've concluded that....

    ...the only way to attain line balance via equal length of both input and return pipes in a reverse return system is to have the first and last radiators in the system approximately equal distance from the boiler. Does anyone disagree with this? If so, what am I not understanding? Input pipe exits boiler and continues run until it reaches last radiator; return begins at last radiator and continues back to boiler. If first and last radiators are same distance from boiler, then input and return pipes will be of approximate equal length. I do not see any way around that rule.

    The counter argument I've heard here is that if you are using TRV's, then it really doesn't matter if the the system is imbalanced.

    ...And still another argument I've read here but don't fully understand is that a lengthy input run back to the boiler doesn't necessarily create system imbalance, and that balance is measured in the region between first and last radiators only. This may be correct but I have no clue on the physics involved with this theory. I'm hoping someone a lot smarter than I will come along and provide a thorough explanation of system balance in a reverse return system: how it's measured/ where it's measured/why a lengthy return pipe doesn't affect it.
    This post was edited by an admin on October 18, 2013 1:28 PM.
  • Gordy Gordy @ 1:29 PM
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    Head and flow rates in parallel

    With out any control valving head in a parallel piped system will balance equally among circuits. Flow rates will vary though depending on the head loss of each circuit. By adding the extra pipe for reverse return you are adding more head loss to the system piping.


    How long is the main supply / return piping? With out the added piping for reverse return.

    How much difference is there in each circuits length?
    This post was edited by an admin on October 18, 2013 1:32 PM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 1:35 PM
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    Question for Gordy

    Not sure what you mean by "How much difference is there in each circuits length?" I'm a hydronics noob and not completely familiar with the jargon. Are you asking for the distance from where the radiator input leaves the main supply pipe and to where it enters the return pipe, for each radiator shown?

    For your first question, I'll take precise measurements and respond shortly.

    This post was edited by an admin on October 18, 2013 1:36 PM.
  • Gordy Gordy @ 1:40 PM
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    That is a circuit or loop
  • Gordy Gordy @ 1:39 PM
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    If you think about it

    Parallel piped is really like a longer version of a hydronic manifold. What it does do is decrease head loss in a system verses a home run set up do to larger dia supply/return piping. How much really depends on the area you are trying to heat. There is also remote manifold stations
    This post was edited by an admin on October 18, 2013 1:42 PM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 2:46 PM
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    Answer to Gordy's distance questions

    "How long is the main supply / return piping? With out the added piping for reverse return."

    Total input piping = 123 feet (as measured from the boiler to the last radiator)
    Total return piping = 83 feet (as measured from the first radiator to the last radiator; i.e., excluding the long return from the last radiator back to boiler)
    Return Pipe from last radiator back to the boiler = 123 feet

    "How much difference is there in each circuits length?"

    Each radiator will be located 5' from the input/output pipes. Therefore a total of 10 circuit feet excluding the radiator (5' input to radiator; 5' retrun to return pipe). All radiators are approximately the same size.
    This post was edited by an admin on October 18, 2013 2:49 PM.
  • Gordy Gordy @ 6:47 PM
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    I think

    Your well balanced already if your radiators, and circuits are as you state. Your main supply / return should be close to identical lengths with out the addition of a reverse return pipe length added in,

    At 123' your supply temp may lose a couple of degrees by the time it gets to the last radiator, depending on if the pipe is insulated, and or if it's in a conditioned space.

    I think I would opt for TRVs skip the reverse return, and go. The TRVs will give you zoning.

    If your not happy with the result you could always reverse return later, but I personally am not seeing a gain here with reverse return being your circuits are pretty much going to have the same head loss.and if you are going to use TRVs. If your not going to use TRVs then reverse it.

    Remember pipe sizing plays a crucial role. In both the ability to deliver the required flow rate, and btus needed. With in the acceptable velocities for a quiet comfort system.
    This post was edited by an admin on October 18, 2013 6:51 PM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 7:08 PM
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    Response to Gordy

    Gordy, thanks for the response.

    When you say to abandon the reverse return would you go with a direct return as an alternative? That was my original design (see the diagram in the first post on this thread).

    I was planning on 3/4" supply and return piping, and 1/2" to/from each individual radiator. Is this sufficient? In either scenario (reverse or direct return), should I be concerned about shrinking the pipe diameter in the supply and/or return as I move further from the boiler?

    I had a friend suggest a 1" input/return pipe size. This seems excessive in this small system.
  • Gordy Gordy @ 7:31 PM
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    My answer

    Direct return with TRVs.

    Reverse return with out TRVs.

    With out knowing the heat loss, and radiator sizes can't say on pipe sizes.

    But larger is better to reduce head loss, which reduces circulator sizing, which reduces electrical consumption.

    3/4" copper pipe can deliver 42000 btus in the 2-4 FPS velocity range. You want the circulating water to move fast enough to keep air in solution, and slow enough to avoid velocity noise, and pipe erosion.
  • Gordy Gordy @ 7:14 PM
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    Red flag

    Did you do a heat loss calculation room by room for your home?

    Seems odd that all rooms would require the same size radiators? Not impossible.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 8:30 PM
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    Yes, I did a heat loss calculation every The rooms are approximately the same size and so are the radiators. Good that you asked, though :)
  • Gordy Gordy @ 6:07 AM
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    Heat source

    What are you using for a boiler Scott?

    What is your heat loss?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 2:41 PM
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    Boiler is an older AO Smith Hydronic Copper

    1960's or 70's era, 80,000 BTU output. It originally heated a in-slab radiant heating system in a 1,200 sq ft home. The in-slab system failed many years ago and the house was retrofitted with a fin-tube baseboard system in the 1970's, which was old, rusty, and generally crappy looking when I purchased the house. I did a major remodel on the house: added 350 sq ft (now 1,550 sq ft tot.), completely insulated (walls/roof/dual pane windows), and removed the crappy old baseboards from all rooms. I'm now planning to replace with an all Runtal radiator system. The boiler has been checked out and is functional (it pumps hot water).

    The home is a slab on grade with a flat tar and gravel roof (yup, no attic or crawl space).
    This post was edited by an admin on October 19, 2013 2:42 PM.
  • SWEI SWEI @ 10:33 AM
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    So what is your total heat loss?

    You can size panel rads at 25-30F ∆T, which will reduce flow requirements.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 2:57 PM
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    Total heat loss response

    I initially used the SlantFin Corp heat loss software Hydronic Explorer 2 to calculate heat loss.. The calculated result was about 20 BTUH/SqFt which was a bit lower than I anticipated. I live in Mountain View, in the San Francisco Bay Area. I've read several "rule of thumb" heat loss articles and the suggested number for San Francisco is 25 BTUH/SqFt. I live about 40 miles south of San Francisco where the average temps are higher than SF so maybe 20-25 is the right number?

    I talked to a Hydronics installer awhile back and he said 25 BTUH/SqFt was about right for my area but that he uses 30 BTUH/SqFt for his jobs.....he said it's better to plan for those rare uber-cold days.

    I'd appreciate comments on it better to overshoot BTUH/SqFt to account for rare cold days? What is the downside to sizing radiators a bit on the high side? I want to avoid overheating...we like a warm but not hot house.
  • SWEI SWEI @ 3:10 PM
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    BTUs per hour per square foot

    depends on both your location and the construction of the house.  We're building now at 12 BTUs/sq ft with an outdoor design temp of 10ºF.


    What was the calculated heat loss for the whole house from the Slant/Fin app?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 3:35 PM
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    Response to SWEI

    I'm in the process of re-entering my data into the Slant/Fin's been over a year since I did it and I want to do it again to make sure it was done correctly. I'll post the numbers in a bit.

    What do you mean when you say: "DO NOT OVERSIZE A HEATING BOILER"? Are you saying that the boiler shouldn't have excessive BTU output? Or are you saying not to over estimate BTUH/SqFt when sizing radiators? Please be specific....I want to fully understand your concern.

  • SWEI SWEI @ 3:43 PM
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    means installing a boiler which is larger than your design day heating requirement.  There is already a safety factor in the heat loss calculated by the software, so in most cases a boiler that is 5-10% smaller than that number will work just fine.

    More specifically in the case of a modulating/condensing boiler, pay attention to the minimum modulation rate of the boiler.  Aim for 1/3rd of your design day heat loss or less on that.  The larger this ratio, the more time the boiler will spend at the bottom portion of its modulation curve, which improves both efficiency and comfort.

    On the radiator sizing, be aware that most manufacturers rate their products at 180ºF or 190ºF.  Radiators are sized using the average of supply and return water temps, so a 180ºF rated radiator running at a 30ºF ∆T would need 195ºF boiler water to deliver that rated amount of BTUs.  Size them for 120ºF - 140ºF using, make sure they will fit the available space, and you will end up with a quiet, comfortable, efficient system.
    This post was edited by an admin on October 19, 2013 3:52 PM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 4:11 PM
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    Boiler size

    SWEI, I'm still working on the SlantFin boiler has an 80,000 BTU output and my whole house requirement will be 45,000 BTU or less. Are you saying my boiler is too large?

    In general, I'm having a difficult time with the jargon you are using...remember, I'm a neophyte and terms such as "design day heating requirement", "modulation rate", etc. etc. have no meaning for me. I guess I have a homework assignment...or perhaps you wouldn't mind putting some color on your suggestions....I think you're making important points, I'm just not following.
  • Gordy Gordy @ 5:35 PM
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    all most twice

    the size needed.

    Modulation rate: is like the accelerator on a car in the modulating condensing boiler category. They have a turn down ratio usually 5:1. They folow the load with supply sensor to try and match it thats what makes them efficient.

    A regular cast iron boiler is not modulating, and you get full output every time it fires.

    Design day is the coldest day of an average heating season. Usually occuring 1% of the heating season. Thats why its important NOT to oversize.

    You must plug in the correct numbers in the heat loss program or it will be off. especially design day.

    IF you did an envelope upgrade while renovatings the boiler will really be oversized even though you added 350 sf.
    I hope you are ditching the boiler.
    This post was edited by an admin on October 19, 2013 5:48 PM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 8:11 PM
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    SlantFin heat loss program

    I have an issue with the SlantFin Heat Loss calculator app: The "Ceiling Factor" drop-down choices do not match what I have. I have a tar & gravel built-up roof with 4" of rigid foam sheathing beneath the tar and gravel. Total R-factor is 25. There are no selections under "Ceiling Factor" that come close. I've concluded the app is useless without a correct ceiling factor for my home. Dead end.
  • Gordy Gordy @ 11:43 PM
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    Not the assembly will work for what you have.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 12:09 AM
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    Gordy re: Ceiling R-factor in Slant/Fin app

    Gordy, could you clarify?  I would need to know the decimal factor for R25 and it's not among the menu choices.  How  would I determine the decimal factor for R25?
    This post was edited by an admin on October 20, 2013 12:20 AM.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 8:16 PM
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    Am I ditching the boiler?

    Hadn't planned to. What are the ramifications of using an oversize boiler other than added annual fuel cost? A new boiler is what, $4-5K installed? When I balance that against a couple hundred/year added fuel cost, the math says to wait until the old boiler breaks down before replacing.
    This post was edited by an admin on October 19, 2013 9:58 PM.
  • SWEI SWEI @ 10:54 PM
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    Keeping the boiler

    while maximizing comfort and efficiency would involve adding a buffer tank (smart plumbers know how to repurpose an electric water heater for this) and a motorized mixing valve running on Outdoor Reset Control.  The delta in materials cost for this versus materials cost for a small mod/con boiler (which removes the need for the foregoing bits) is less than the labor cost for either solution.

    Translation:  Have a properly sized, quality mod/con boiler installed by a competent radiant professional.  Sit back, enjoy the outrageous comfort, and brag to all your friends about how little you spend heating your house.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 11:16 PM
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    I'd rather brag to my friends...

    ...about the smart economic decision of keeping a perfectly good boiler rather than blow several thousand on a new boiler for which the payback is maybe 10 years.

    Seriously, though, other than fuel cost are there other significant downsides to keeping the old boiler in service?
    This post was edited by an admin on October 19, 2013 11:18 PM.
  • Gordy Gordy @ 11:39 PM
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    like maybe lasting this year or 5 years, and installing a new one plus the xtra fuel consumption.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 11:46 PM
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    Could you elaborate? Are you saying the piping and/or radiators could fail in 1-5 years?

  • Gordy Gordy @ 1:05 AM
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    The boiler is quite old 40 plus years minimum is pushing the limit.
  • SWEI SWEI @ 12:31 PM
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    Keeping the old boiler in service

    will require replacing enough of your current system that (if it were my house) I'd be quite leery of making the investment.  Given that the existing boiler puts out twice the heat you need on the coldest day of the year, it's going to be short-cycling the overwhelming majority of the time.

    Assuming you still want to take this approach, I would strongly suggest adding a buffer tank.  If you size the radiators for a low water temperature (please do) and set the boiler aquastat for 150F/130F, TRVs will throttle back the flow and deliver some comfort.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 12:49 PM
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    Questions for SWEI

    "Keeping the old boiler in service will require replacing enough of your current system"

    Not sure what you mean by "old system". I have no system today, just the boiler. I'm building the system from the ground up with new radiators.

    What will it cost to have a technician install a buffer tank on my old boiler? And are you saying that it is possible to lower the temp output of my boiler? To what temp?

    See my new post down below...I'm concerned about sizing radiators to 180 degree water than having to install a new boiler later that has a lower water temp...and then i'd have undersized radiators. Do you have any idea what temp my old AO Smith be adjusted down to?

    What is the most common/typical water temp in the new 40,000-50,000 BTU output boilers?

    This is a very valuable discussion....I'm beginning to see some potential flaws in my planning/thinking.

    Thank you
    This post was edited by an admin on October 20, 2013 12:57 PM.
  • RJ RJ @ 11:03 PM
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  • Gordy Gordy @ 2:03 PM
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  • Gordy Gordy @ 4:03 PM
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    Good advice from SWEI there

    I was kind a wondering, and leading up to SWEI's questions. That program is closer to 15% padded.
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 12:29 PM
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    SlantFin heat loss calculator question

    I'm stuck at "ceiling factor".

    The input field calls for a decimal factor to be chosen from a drop down menu. Problem is that my ceiling is at tar/gravel built up over foam boards that amounts to R=25 and that is not among the choices. Any thoughts on how to convert R=25 into their equiv. decimal factor?
  • Scott_Mountain_View_CA Scott_Mountain_View_CA @ 12:39 PM
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    Boiler questions

    Could someone explain to me the relationship between boiler water temp, boiler input BTU, boiler output BTU and radiator sizing.

    My current older AO Smith is a 80,000 BTU output @ 180 degrees. I had planned to size my Runtal radiators based on 180 degree water temp.

    I notice in the Runtal literature a table that shows different temps and the required adjustments in radiator output based on those different temps.

    It seems obvious to me that if I size my radiators for 180 degree water and then later replace the boiler with a new one that produces a lower water temp, my radiators could become undersized (for the new, lower water temp). Could one of the pros comment on this? Is this a valid concern? What is a typical water temp in a new boiler?
  • Gordy Gordy @ 7:31 PM
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    The Basics

    And size your rads so in the future when your boiler dies you can get a more efficient one, and use lower temp water to do it.
    This post was edited by an admin on October 20, 2013 7:32 PM.
  • SWEI SWEI @ 10:38 PM
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    Boiler water temps

    The lower the temperature of returning boiler water, the cooler the flue gas -- and the greater the combustion efficiency.

    In a conventional cast-iron boiler, that returning water temperature must be kept above 130ºF - 140ºF (depending on the specific fuel in use, the humidity) in order to prevent flue gas condensation from rotting out the flue pipe and boiler heat exchanger.  To maintain a reasonable degree of system efficiency, the supply temperature should be at least 20ºF hotter than this.

    A modulating condensing boiler has no lower limit on its return water temperature (OK, perhaps 34F might be a good idea.)  This allows efficiencies over 98% when paired with a properly designed emitter system.
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