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Joined on January 19, 2012

Last Post on September 15, 2014

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Short cycling

@ March 3, 2012 4:00 PM in Condensing vs Modulating / Condensing

To answer the 5% efficiency question. A non modulating boiler in your application will short cycle to the point where it will greatly reduce efficiency.

Quick math

@ March 3, 2012 3:49 PM in Condensing vs Modulating / Condensing

A boiler with 105,000 input running at 88% efficiency at sea level will have an output of 92,400. If you assume a shower will be 100 degrees and the incoming water from the city will be 50 degrees the numbers look like this: 92,400/500= 182.8 GPM per degree. 182.8/50 degree delta t= 3.65 gpm of warm water to the shower. With 1.8gpm low flow valves you can run 2 showers forever without running out. With old high flows maybe just one shower. The 40 gallon tank can act as a buffer for when the loads are greater. Yes your system is oversized for heat but unless you plan on putting in a larger DHW tank, I think it is pretty close for DHW.

Mod con

@ March 3, 2012 1:16 PM in Condensing vs Modulating / Condensing

I think your idea of a 105 mod con is perfect. A non modulating boiler will short cycle excessively. The mod con will likely have a low end of 20,000 btu. It will run at peak efficiency at this rate. It looks like this is almost a perfect match with one zone calling.As for the DHW I think the 105 will work well. If you measure the GPM of your showers and you know the temperature of the water coming out of the ground this can be easily calculated. I would recommend a firetube style modcon like the Triangle Tube. They are lower maintenance and require less energy in circulators. Lochinvar,Dunkirk and others have similar designs. 


@ March 3, 2012 12:45 PM in Expansion tank issues

Boiling point at 10,000 feet is around 190 degrees. It does effect cooking and requires boiler temps to be set a bit more cautiously. I agree that the system pressurized at one altitude and moved to another would read differently. However if you charge the tank and fill the system at a given altitude, What is the difference? Perhaps ME will weigh in on this?

Did you check the pressure?

@ March 3, 2012 11:30 AM in Question

Obviously the right thing to do is to bring it to code. I am curious how the existing set up is working in the real world. If you turn on all the loads does the pressure drop?


@ March 3, 2012 11:19 AM in Expansion tank issues

Humm! Do you have a photo. Maybe there is something you are missing that someone on here can find? Double check valve?


@ March 3, 2012 11:19 AM in Expansion tank issues

Humm! Do you have a photo. Maybe there is something you are missing that someone on here can find? Double check valve?

Personal preference

@ March 3, 2012 11:16 AM in Radiant floor with domestic h20

There are quite a few ways to do this. How much detail are you looking for? You need to pump from the hot water heater in the exchanger. My plan for the other side would be to use a variable speed pump controlled by a tekmar 356 with outdoor reset to in inject the water into the radiant loop from the exchanger. This way you can control the floor temps and avoid dragging down the hotwater temp using the boiler protection feature on the controller. You will of course need air eliminators,zone valves, pumps ect. to control the radiant side.

Water off?

@ March 3, 2012 10:57 AM in Expansion tank issues

Sorry I did not see you had tried to turn off the water. Was the expansion tank functioning correctly with the water off, of was the level changing? Have you tried isolating the secondary loop and just running the boiler loop? It seems the problem must be related to the 0014 in relation to the high head boiler. I assume you have triple checked your pump directions?

Keep us posted

@ March 3, 2012 10:21 AM in Expansion tank issues

This is an interesting one. I think Mark is on to something, although I would expect the problem would occur on pump shutdown. The flashing to steam would make sense but only if you were pumping away from the high head loss boiler.
Icesailor, could you please explain pressure over 5000 feet? Since the pressure is relative to the atmosphere,I am not sure what you are saying. Your example of air locking makes sense. You should have the pressure from the building height + a safety margin. The building you describe would need 15 to 20# depending on the height.


@ March 3, 2012 10:05 AM in Radiant floor with domestic h20

Unless the heater has a "closed" hydronic coil. Don't do it. Just because some manufactures are enabling people to put in unsafe systems, it is still the wrong way to do it.


@ March 3, 2012 9:59 AM in Best radiant design for new build

What are are your local electricity costs? Also what else is available for fuel as well as costs? Wood, pellets, propane? How will you heat your domestic hot water?


@ February 29, 2012 11:27 AM in radiant heat loss because of pex placement?

I was thinking you were comparing carpet and pad at R 1.4 to2.0 depending on type, to tile at .3. My personal experience in setting up reset curves has led me to think it is in the 10 degree range. I realize there is a serious SWAG factor. As a rule, I don't argue with Siggy!

I agree

@ February 29, 2012 11:03 AM in Your thoughts please...

I am getting ready to do some some work on some very similar sounding systems.
I have yet to do the combustion tests but have observed significant short cycling. My plan is to increase the differential on the main loop and tune the boilers. If that does not control it, I am thinking about a buffer tank. Great subject!

How low can you go?

@ February 29, 2012 10:55 AM in Mod-Con with Convectors?

I know there are to many variables to be exact. What kind of numbers are you guys using for the heating curve with baseboard. I am assuming the coldest day would be 150 to 180. Are number like 100 working on the warmest?

high numbers

@ February 29, 2012 8:21 AM in radiant heat loss because of pex placement?

A do not believe the 50 degree numbers are correct. I use "radiant precision" as a reference on this kind of stuff. The 2" insulation is going to provide a good protection against downward heat loss. The lack of perimeter insulation will have some impact, less it is below the frost layer. With good downside insulation the heat is not lost, It just takes more time to get there. I would estimate a 10 degree water diff. It would take considerable brain damage to guestimate the energy savings, A SWAG would be a couple of percent of the total heating bill. I don't believe that from a cost savings point of view the tile is worth it.


@ February 28, 2012 5:31 PM in Indirect tank proximity to boiler

Indirect is the right move. You will have abundant hot water at a cost of a least 1/2 of electric.
Make sure it is set up as priority over the heating load and piped so it will get the full output of the boiler without causing the boiler to condense.
I think I would install it next to the boiler. You would have to run 2- 1" lines 40' and have a floor drain at that location to move it across the house.
I am not a fan of the "comfort" circulator. I have one in my house and the cold water is always warm (were do you think the warm water from the hot water line goes).
If you have access, why not run an insulated 1/2" pex run and use a grundfos regular circulator with a timer and aquastat?

Turn it off

@ February 28, 2012 5:01 PM in A question about Circulators on Packaged Boilers

I do not know the reasoning behind "always on" hot water boilers and pumps. It make tank stratification impossible and tend to wear the pipes, pumps and boilers.
I recently put a tekmar 150 setpoint controller on the tank and used it to turn off the boiler which in turn controls the pump. The nice part is you can set the differential to get the optimal cycle time.

A couple of thoughts

@ February 28, 2012 12:23 PM in Lochinvar Knight boiler problems

Bob, as usual has this problem accurately evaluated.
It appears as though the service tech may be attempting to troubleshoot by just replacing all the parts. Has he been working with Lochinvar to determine the problem?
I think that is is very likely the problem is being caused by something like,poor combustion,2" intake, overpumping, oversized boiler. and the tech is convinced the controls are at fault.
How long does a typical boiler cycle last?
Does this model have a combustion test port?
Is there a hole drilled for one?

Dead Subject

@ February 17, 2012 5:23 PM in New Lochinvar Knight Installation

If "unhappy" is "unwilling" to post a picture, I think this subject is dead. Installation has a huge impact on both efficiency and longevity. If a boilers electronics are designed for a certain number of cycles, A severely short cycling boiler will greatly reduce the life of the boiler. It is impossible to blame lochinvar without more info. I am working on 4 boilers now that are 5 years old and short cycle horribly.Many control parts are malfunctioning.

Boiler Control

@ February 17, 2012 3:34 PM in Buffer Addition

I am heading out on vacation for about a week. I am assuming your mixing valve will be adjusting for outdoor reset. The target water in the tank and the water flowing to the tank from the boiler will mixed to outdoor reset. This temp will have a target and differential.

On the other side The boiler is going to be set up to run with a return no lower that 135 and a supply of say 145 to 185. Because the boiler is returning some of the water back to itself, it can have it's own temp and diff.

If I were trying to get an accurate buffer size, I would calculate the boiler+water and it's delta T and add it to the buffer tank+zone piping and it's delta T. Then I would figure the extra boiler heat not being absorbed by the heat load and go from there.

Sounds Close

@ February 17, 2012 2:29 PM in Buffer Addition

The boiler turndown is higher than I would have thought.It is hard to get it exact without all the system volumes.It sounds like 40 or 50 is appropriate. In a perfect world your boiler will fire on a fairly wide differential (145 to 185?)and your tank  will have a tighter one maybe 10 to 20 degrees and based on outdoor reset. Make sure you boiler pump stays on anytime you have a call for heat. If it is controlled by the boiler and the tekmar turns the boiler off, you won't be utilizing the mass of the boiler and its water.
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