Boiler oversized, should I turn it off?
Hey Everyone. First post here; looking for recommendations to deal with my home being too warm (if you can believe it 🙃) .
Current setup:
- 1950's home, 1,200 sqft heated space (1st floor)
- 25 year old 100,000 BTU Weil-McLain oil boiler, hydronic baseboard heat, 1 zone. Professionally serviced annually
- Chimney with stainless liner, 20 feet vertical
- Honeywell L7224 Aquastat Controller. Low_SP = 160°F, 10° differential. High_SP = 180°F, 10° differential.
- Simple digital thermostat with programmable profile.
I've lived in the house (located in southern New England) for ~10 years. I've been making improvements over the years to the energy efficiency of the house (new windows, insulation, etc…). The most recent improvement was I had the roof replaced this summer (including all the sheathing), and a lot of improved insulation was installed in the rafters at this time (it's a cathedral ceiling).
In the first couple winters living here, the boiler struggled to keep the house ~60°F during the winter, and wouldn't get above 55°F on the coldest days. Now, I have the opposite problem - the house is at ~72°F during the day without the heat zone circulating - this is just the radiating heat from the boiler sitting at it's "low temp setpoint". The thermostat isn't ever turning on, because I have it set to 65°F in the day, and 60°F at night.
The boiler turns on every ~25 minutes to keep the water temperature at 160, and runs for 2-3 minutes before turning off. I'd like the house to be cooler to save on oil, but also for comfort (>70 is just too warm 😓)
Should I do any of the following:
- Leave things alone, maybe open the windows during the day?
- Turn off the boiler at night?
- Lower the setpoint for the "LOW" on the Aquastat?
- Increase the differential on the Low_SP?
- Think about replacing the oil boiler with a new one, that is smaller BTU?
Comments
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Sounds like there is an issue or possible more than one with the circulator. Sounds like there isn't a flow check on the heating circuit or it is manually open or stuck open and sounds like the circulator isn't working or the system is air bound. Are the emitters warm or hot when the thermostat is off?
Why is it set up warm start, is there a tankless coil for dhw in the boiler?
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Boiler is not responsible for domestic hot water. I have a hybrid electric/heat pump water heater in the same room as the boiler to handle that (Bonus - the excess heat from the boiler is used by the heat pump)
The baseboard heaters are warm to the touch. However, I can confirm that the water circulating pump for the zone is OFF. When I crank up the thermostat, I can hear / feel the pump turn ON for the zone by placing my hand on it, so it will circulate when required. Also doesn't sound like there is any air in the pipes (no knocking sounds, etc…)0 -
You can turn the lo setting as low as it will go and it won't fire the boiler unless there is a call from the thermostat assuming the thermostat is wired to the circulator relay and the boiler. Was there a tankless coil at some point? That is really the only reason to make it warm start.
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Unless there isn't enough baseboard to output the 80,000 btu/hr or so output of that boiler it should have kept it warm even before, that is very likely oversized even for before the improvements.
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Please do this:
To use the L7224U in a cold start boiler application,disable the Low Limit function by pressing the UP arrowbutton, DOWN arrow button and I buttons simultaneouslyfor three seconds. Then push the I button until LL isdisplayed. Then press the down arrow button until OFF isdisplayed.
Also, set the HL to 170 while you are in there.
Done.
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Ok, I follow. I have downloaded the controller user manual, so I know the key combinations to make adjustments. I will try that out.
In this cold-start setup, is the boiler less efficient by needing to heatup from <80°F all the way to 170°F when heat is required? How about mechanical ware-and-tear - is it better to run for a long time (the initial heatup) vs many short starts throughout the day?
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Running the boiler cold start in your situation will be both more fuel efficient and easier on the equipment, which will prolong its life.
—
Bburd1 -
This is a cold start setup.
The boiler is MORE efficient because you are not maintaining 160F when you don't need it. The boiler sits idle until you DO need it and then it climbs to 180F.
I do think you don't need anywhere near 180F to heat that building. Experiment with 170F for HL. If that works, experiment with 160F. Somewhere, you will not be happy because the boiler won't heat the building. I cannot tell you if that value is 160F or 170F or 180F. It depends on the outdoor temperature. For the greatest efficiency, you adjust HL based on the season. You need higher HL in the dead of winter but you certainly don't need it in September or in April.
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That control provides all the capability you need to maximize efficiency. You just need to use it. Personally, I find it the best aquastat you can procure.
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Thanks for the information out everyone. I'm going to try the LL = OFF, and HL = 170 setup and see how that works
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Understand 170F is not fixed for all time. If it works at the design temperature (the lowest expected temperature of the winter), you absolutely don't need it in April. If the outdoor temperature averages above 30F, you LIKELY can reduce the 170F to 160F. You may be able to reduce to 155F but do not go below that value due to condensation issues. Consider this an experiment.
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We have a similar Weil-McLain boiler only slightly larger than yours, for 2,400 sq ft, also in New England. The boiler also runs from a cold start. Depending on your radiators and how much water you have in the system, your boiler may never even reach the high limit temp. Our boiler starts cold, typically runs 30-40 minutes, and stops at around 130-140 degree water temp because by then the thermostat is satisfied. So we never come near shutting down on the high limit.
You have half the square footage with roughly the same size boiler, so you probably have fewer radiators and less water. That means your water temp will rise faster than ours. So your may hit your high limit and shut down before the thermostat is satisfied.
Either way, as you say, your boiler is massively oversized. You probably have 3-4 times the heating capacity that you actually need. Save your fuel records for the year, and from that someone can do an accurate heat loss calculation to correctly size a new boiler when it needs replacing.
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Understood. I was going to ask if there was a "too low" setting. Getting the fire hot enough for condensation to boil off makes sense.
Related question: what do you all think about turning the boiler off during the summer? I typically do this and start it once a week to heatup to temperature for condensation to evaporate.
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just turn it off in the summer. or not. if it is set up cold start it won't come on anyhow.
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We leave our two Weil-McLain WGO-5 oil boilers turned off all summer, and we don't bother running them. We have the oil company come in September to service and clean them, new filters, nozzles, set the combustion, etc. That's it. This works well for us.
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As Matt mentioned, a cold start boiler will NEVER start in the summer. The thermostats will never close. So "turning it off" is, essentially not required.
Sure, you might not want to boiler to start it in late April or early May…………but, this is simply accomplished by keeping the 'stat below the room temperature. No need to even go down to the basement. :)
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If the baseboard are warm or hot when the zone isn't running, then that's what we call a heat rise. There should be a Flo valve on the boiler that prevents the hot water from traveling through the zone unless the circulator comes on.
You can also make the aquastat cold start. High 160°, Low off.
Looks like I'm being redundant.
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If it is a single zone and doesn't provide dhw and is cold start it doesn't need a flow check.
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