This thread has been bookmarked. Visit your bookmarked threads to review.
Post a Reply to this Thread
Can I get more efficiency from my old boiler? (23 Posts)
Can I get more efficiency from my old boiler?Can I get more efficiency from my 1988 6 zone natural gas boiler? For example can an electronic igniter replace the pilot? Can a modulating burner replace the full on burner? Can it be adjusted and/or cleaned? I'm told there is nothing to adjust.
I live near Boston and keep the heat low but my gas CCF usage is 3-4 times my old similar sized house with condensing gas forced hot air furnace. New house has more window area and higher ceilings but better insulation and air sealing.
I started getting quotes on a Mod/Con boiler. But they run 4 times what it cost to install the condensing gas forced hot air furnace at the old house.
I mention the pilot/igniter because I can hear that it is a large flame. I turned off all thermostats and read the gas meter over an hour. The bottom dials on the gas meter are a bit hard to figure out but if I got it right the pilot is using 2 CF per hour, which is 14CCF per month or about 10% of November usage at the new house or 34% usage compared to old house. (These are rough numbers - I did not turn off HW)
Burnham P-208-W Installed 1988 Manufactured 1983
DOE HTG cap - 190,000
Water BTU/hr - 165,200
Input BTU/hr- 232,000
Gas pressure - 14 max and 4.5 min
Manifold pressure - 3.5
ASME max working pressure
Water - 30 psi
Min relief cap - 232
QuestionsJust a couple starter questions. Do you know the heatloss of the home? How many square feet? What type of heat emmiters (cast iron rads, baseboard)?
QuestionsI don't know the heat loss. I'll try to get it from one of the guys quoting the Mod/Con. We just had a cold 9 F night and we were warm enough.
3500 square feet
2 more photos attached
YesIn response to your first question "can you get better efficiency" the answer is yes. How to achieve it is the main question. Can you post pictures of the boiler and associated piping as this will help us understand what you are working with.
Heating systemBased on the size of your home and the size of your boiler you're at 50 BTU's per square foot! Your boiler is grossly oversized (probably at least by doube)! The fact that the boiler is almost 30 year old and has had a hard life due to short cycling means that it is time to go. The good news is that with a properly sized boiler (preferably a mod/con) your bills will be drastically reduced (get rid of that energy hog water heater and put in an indirect while you're at it). I would feel safe saying that you will save at least 50% off your current heating bills. Get rid of those six zone circulators while you're at it and save on electric as well. Make sure the contractor you choose does a heatloss of the home (if he doesn't, throw him out the door). Whee are you located? Maybe we can point you to a good contractor.
More?Thanks for the replies. I'm new to this.
Mod/Con install is too expensive at this time. I want higher efficiency from my boiler.
Can an electronic igniter replace the pilot? Can a modulating burner replace the full on burner, Can an outdoor temp sensor be wired in? Is there any kind of wast heat recovery system that can be added on?
When you say "Get rid of those six zone circulators" do you mean convert to one zone with one pump?
I don't know if I am short cycling - how can I tell? Did you infer that I am short cycling from the boiler being too big? What results from short cycling? Cracks? Leaks?
Yes more picturesI'm not a professional...
1. Post more pictures so the pros can confirm that everything looks installed correctly.
2. It is worth your time to do some online research and learn how to do a heat loss estimate for your home. Do a couple of them from different websites so you're confident in the numbers.
3. If the boiler is good and the size is appropriate for your calculated heat loss, get yourself an energy audit. Your home shouldn't be losing that much energy and they should be able to point out what you could improve --probably stuff you could phase in over an extended period to match your budget. At the very least they will nail down the heat loss estimate.
However, most likely RobG is right. Let's say you only need less than half the btu's your boiler is rated for. In this case you have six zones of low mass baseboard requiring on average substantially less than 1/12 of what your large high mass boiler is attempting to output. The questions I would be contemplating:
1. Are the pumps configured to post purge the hot water out of the boiler after the burner shuts off?
2. Is there a vent damper to prevent heat escaping up the flue between its frequent cycles?
3. Are the thermostats coordinating their calls for heat? (this is called zone synchronization)
A lack of zone synchronization can exacerbate the cycle problems associated with an improperly sized boiler. I would think this would be particularly true with baseboard emitters. The frequent cycles will keep your boiler perpetually hot. If the boiler is not utilizing post purge and a vent damper, this heat is sent into the basement or up the flue.
Contemplate having an undersized two-stage non condensing boiler installed with a zone manager capable of providing zone sync, post purging, and zone load shedding. That last feature, zone load shedding, would allow you to automatically reduce boiler demand by shedding non critical zones. The idea here is to install a smaller boiler that better matches average demand rather than peak requirements. However, one or two zones will go with out heat during freak cold weather, if you don't have a suitable home layout it's not going to work. I mention this because a downsized non condensing boiler with the proper controls will close much of the efficiency and comfort gap that exists relative to a mod/con, yet be substantially cheaper and easier to install.
Outdoor resetIf in fact your boiler is over-sized there are a couple things that can be done to help lower the energy usage.
Taco and Tekmar (among others) have boiler controls that utilize outdoor reset, this will make use of all that stored energy in that huge cast iron heat exchanger; allowing for less on cycles throughout the day.
If the boiler is in good working order, the right contractor can access the current controls and make a recommendation. Adding outdoor reset can achieve anywhere from 10-30% savings [based on my experience with the Taco and Tekmar controls]. Your mileage may vary in relation to the actual amount the boiler is over-sized, the footage of baseboard installed in each room and the operating temperatures needed as indicated by a proper heat loss calculation and measuring of the system.
Variable speed pumping may also decrease your energy use when coupled with a proper boiler control strategy. Ultimately, if replacement is not in the budget for now, consider paying for a proper heat loss and design with ODR as a focus.
Good luck!"If you don't like change, your going to like irrelevance even less"
NoThe answer to your question is NO! Unless you feel picking up 1 or 2 percent by changing over to electronic ignition is a wise investment. I don't. You question really relates to system efficiency not boiler efficiency.
Best investment without a boiler change has been pointed out by others. Have a complete room by room heat loss done, have that loss broken out per zone, measure all heat emitters for capable btu/hr output at various water temperatures per zone. This will allow you to find your outdoor reset curve.
Add an outdoor reset control like a Taco SR501OR. Get rid of all the circulators and change them to Taco Zone Sentry's. Add a Taco Bumble Bee Variable Speed circulator as a system pump. I would also pipe in a boiler bypass for boiler protection from cold return water temperatures
Other then this there really isn't much more you can do with they system. ."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
Reset ControlDoes a reset control control two setpoints - the high temp turn off point and the low temp turn on (if any zone is calling)?
If the reset control lowers the setpoint(s) when the outdoor temperature is mild, won't my cycles become even shorter? I think the burner is just full on/off.
My cycles are 1-2 minutes and it seems to shut off around 190F and turn on around 160F.
What is the benefit of removing zone circulators?
Do you think I measured wrong when I came up with 2 CF/hr gas consumption by the pilot? By my calculations (above) the pilot was 10% of November usage.
I am working on the heat loss - thanks!
A few thingsRegarding the pilot light:
When you measured the gas usage, did you turn off all other pilot lights? stoves, fireplaces, etc? (You mentioned the HW, but are you sure there is nothing else?
What does 14ccf cost you over there?
My understanding is that any sane ODR control would be configured to allow the boiler to run up to a higher temperature if it detects short cycling. And yes, one or two minutes is sever short cycling. The question then is how to get the remaining heat out of the boiler and distribution system?
Regarding the pumps:
How are the pumps configured to operate? When a zone calls for heat, what happens? Less zone circs implies better electrical efficiency, but since your boiler is only running a short period every hour, your pumps are probably not being used much at all. It would be an issue if they were all running all the time.
Pilot $20/moPILOT USAGE 1 hr
approx. 2 CF/hr
2 x 24 x 30 = 1440 CF/month or 14 CCF/month
14 CCF x 1.0293 (thermal factor) = 14.41 therms
Cost per therm $0.53 (usage) + $0.19 (distribution adjustment) + $0.63 (delivery) = $1.35
14.41 therms x $1.35 = $19.45
So about $20/month just for the pilots on a $200 gas bill for a mild November with conservative (60F and below) home heating.
The only pilots are boiler and HW.
When a zone calls for heat the boiler fires and the zone pump starts - I can feel a slight vibration. When the zone stops calling the pump stops. At that point I guess the boiler just cools off by wasting heat into the utility room,
Energy savingsI don't think that the current system (almost 30 years old) is worth sinking any money into to try and reduce on energy. As it is a 3500 sf home with six zones, if any one zone calls he is firing 166000 BTUS for that one zone, that's insane! Even with outdoor reset. The only thing that could help would be a big buffer tank (and outdoor reset controls) to store that beasts heat until needed. But then when that 30 year old boiler fails, you then have no need for the buffer tank and the reset control comes as part of most modcon control technology. I would try and find a way to finance a modcon (properly sized) and not waste money now only to have to throw it all away as it won't be needed when this oversized unit fails.
Just my opinion
Give UpYou are probably right, but I don't want a big investment right now.
I would love to know how many years I have left on this boiler. Installed in 1988. House abandoned 5 years 2007-2012 - no heat.
Is there a rule of thumb for the life of a cast iron boiler?
Are there warning signs that a cast iron boiler is about to fail?
When the fail what do they do? Crack? Leak?
BTW you were right about the short cycling. 1-2 min.
Don't give upMy 2 cents:
What are we talking about in yearly fuel bills?
I agree with RobG that investing in this system is a waste, but you could start investing in your next system and cashing out the value of your old boiler.
Can you dezone the controls? I'm suggesting using one or two thermostats wired in a manner that forces the pumps to fire together. If you can use one thermostat then use one of your existing devices. Optional: If you want to use two or three, check out tekmar's, honeywell's, ?others? that are able to sync their zone management. These are high end devices with advanced PID control and cycle management that you will want/could incorporate into your next system.
Now for the fun stuff. Adjust the boiler differential to a much wider setting. Your measurements indicate it's set to fire at 160 and shut off at 190. If the system is worthless and you're prepared for a full upgrade in the next few years, why not set the boiler to dip down into the condensing range? Reset the differential to 140/180 or heck, why not 120/170, your boiler probably has quite a few years that it could rust before failure. (I'm assuming there is no boiler protection bypass installed.) This configuration should give you thermal performance on par with an ODR control and buffer tank, but you need to check that you have a vent damper.
For one or two of the pumps that handle the main zones of the house, hard wire them to a switch that you can flip on for the heating season. Now the boiler will always post purge completely after a call for heat. If you're using two zones, make sure there is a pump running in each zone.
And the obvious:
Have you considered insulating all that copper in your basement?
Can you see what the effect would be? Nearly ten times less cycling, stand by loss, and better thermal and combustion efficiency.
Don't give upYes I'm prepared for a full upgrade, just not this season.
Can you point out in one of the photos where the boiler differential control is? I just want to look and see how it is set.
Wouldn't adjusting the differential temps downward make the cycles shorter? As I understand it, my overly huge burner can't do anything but make huge heat. Surely it would achieve the lower temperatures more quickly and therefore cycle off.
Can you see a vent damper in the photos? I don't think I have one. It would be inline with the flue and have a control wire, right?
I like the zone syc idea - get a longer cycle by creating more demand at the same time.
As for pipe insulation, the home energy auditor from MassSave assured me that pipe insulation is only used for cold water pipes. Who trains these guys?
I only have one month of fuel bills - a mild November with thermostats set at 60 F and below. $205. That's 4x higher than my old house of similar size.
AnswersWhat are the little metal boxes on the front of the boiler?
Most likely you can't increase the differential beyond 30 degrees. But we can look up the model and find out for sure.
Question: "Wouldn't adjusting the differential temps downward make the cycles shorter?"
Generally yes. Lowering temps implies higher thermal efficiency in the heat exchanger, which implies a faster rise in temperature, hence the burner will shut off sooner. Furthermore --on the distribution side, since the supply water temperature is closer to the desired room temperature, less heat is emitted from the baseboard. And, if the thermostat is not satisfied, more burn cycles will be required. Higher thermal efficiency and the associated lower standby losses are good, but if the cycle length is super short you start to loose combustion efficiency. For reference, I believe most controls will try to keep a minimum burn time of two minutes. This is probably more for wear and tear than combustion efficiency though.
However, in your most likely situation (assumption) of extreme mismatch between burner and emitters, I would speculate that it is the differential adj. value itself that is the key variable. It would be nice to keep about the same high limit and set a very wide differential, increasing the range for which the burner will stay off, and using post purge to remove all the stored energy in the system. (Unfortunately, it looks like most differential adjustments are limited to 30 degrees.) The effect would be to move heat out of your boiler and distribution and extend the time period between cycles, hence lowering stand-by temperatures and associated thermal losses. The idea here is to let your house swing in temperature a little bit more, allowing it to act as a thermal buffer. No one likes to live in a thermal buffer, but if your not swinging you're not buffering, and less buffer means more cycling.
If you play around with the aquastat, bear in mind that non condensing gas boilers need a minimum return water temperature to prevent corrosive condensation from forming on the heat exchangers. The condensate forms as a result of low temperature in the exhaust stream and can manifest itself in the flue and chimney too. If there is a boiler bypass and you lower the aquastat too much, I would imagine you would simply be trapping the heat in the boiler, as the function of the bypass loop is to divert water around the unit in the event that the return water temperature is too low. In this case you would need to reset the boiler bypass to allow cooler water. Doing so would introduce the potential issues of thermal shock and excessive delta T across the boiler.
Question: Can you see a vent damper in the photos?
No, but I know nothing about this unit. Maybe it is under the shell? If you don't have one or it is not enabled, I think it is worth the money to have one installed, can't be that expensive. Think about it, all that energy going up the flue and inducing an even stronger draft, 24/7, whether you have the thermostat set at 60 or 70.
Regarding zone sync:
If your zones are calling for heat at separate times, clearly zone sync will cut the cycles by possibly up to a factor of six. This will reduce your stand by loss because the boiler and near boiler piping will have much lower average temperatures. Additionally, because the boiler is now working with a much larger emitter area, the cycle time will lengthen, which might significantly improve combustion efficiency in your situation. However, if your system was poorly designed, you may have issues with excessive flow through the boiler. And simply firing all the pumps at the same time without individual electronic control can cause uneven heating when zones are unbalanced.
Regarding the pilot light:
That really can't be adjusted????This post was edited by an admin on January 13, 2013 7:29 PM.
Bad InvestmentThe investment to properly accomplish what you want and need to do to increase your overall system efficiency is a waste of dollars in my opinion. You have 1950 boiler technology that itself is over 20 years old. The only way to stop the existing short cycling is to add a buffer tank, change piping and add controls.
You need to have a room by room heat loss calculated, emitter capable btu/hr outputs calculated at various water temperatures to find your sweet spot. After you get this use the information to make the right decision which is to change the boiler."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
I agreeI agree with Chris. The old Burnham needs to be repiped with zone valves and a smart pump, spark ignition and new gas valve, ODR control and pipe insulation. There's probably not a liner in the chimney....The repipe costs would be at least 1/3 to 1/2 what the replacement cost would be. Not such a good investment.
No one can predict the life expectancy of the appliance, but it will be sooner rather than later. That being said, cast iron boilers can live a very long life if there's no condensation, even if they're not very efficient.
Where to beginImagine driving a Top Fuel Drag race car in the city. You are going from 0 to 100 miles per hour in seconds, frrom stop light to stop light. You burn 1 gallon per mile where as the Toyota Tercel in the lane next to you is getting 18 miles per gallon. You both are going the same distance, but you are doing it in differant ways. Your thermostat is the stop light. Your boiller is the race car, what you want is the Tercel. There is no way to convert your race car into a commuter vehicle. It's engine is too big.
The only thing that I can see that would help (without replacing the system) is to break your system apart into one or two zones. You mat not save on fuel, but at least you will have a warm house in the meantime. Right now you are keeping your unused zones turned down to try and conserve fuel. It doesen't work that way. You may as well have your zones open and be comfortable because the boiler is firing anyway, take advantage of the unused heat.
Until you are ready to replace the system, you may as well be comfortable in the house.
Just my opinion.
Where to beginGood analogy.
I prefer a cooler house. I'm comfortable.
I can see how turning up the thermostat could pump heat that is now wasted into the house.
But I'm not convinced that turning up the thermostat will save me money. My gas bill gets down to how many minutes per month the burner is firing. That can't be less with a higher thermostat.
MisinterpretationI think you're missing his point. You're not going to save money by turning up the thermostat. It's just that the system has a pretty consistent standby loss whether the thermostats are set at 60 or 65. In other words, you're not saving as much as you think. If you have frequent cycles at 60 degrees, you might as well raise the temperature and warm up. The system, by the looks of your photos, is optimally suited to keep your house at a perfectly stable 90 degrees. (I'm making assumptions about everything.) As a fraction of your heating bill, the standby losses are greatest when the temperature is set roughly half-way in between the outdoor temperature and the system's 100 percent-on indoor temperature. Given the mild conditions, that is exactly what you have it set at.This post was edited by an admin on January 14, 2013 8:59 PM.
You CanLead the horse to the troff. Of course keeping your stat lower is going to reduce minimal fuel consumption but that does not stop the boiler from putting the pedal to the metal. Basic rule of thumb for outdoor reset is, for every 3 degrees I can run my heating system with less then 180 degree water I can save 1% of fuel. The problem with boilers such as yours is you limited in making sure the boiler sees 140 degree water temp. You can pick up 6%-7% fuel savings just by adding an outdoor reset control. But the investment in that with the other proper piping changes will eat up that savings.
You could add a Beckett AquaSmart to increase boiler cycle time. No piping changes."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."