Normal boiler therm usage?
I have been using about 362 therms per month in the winter to heat my home. The house is about 1900 sqft and poorly insulated - although insulation work has been done. I have a boiler and radiators for heat; the boiler is about 40 or so years old. I've had all the radiators bled. I set the heat to 62 degrees 24/7. This is in the Boston area so it has been a pretty cold winter so far.
Does this usage sound high? With the gas prices here the gas bills are nearing $1000 by themself.
Comments
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The usage doesn't seem out of line for the space you describe with a 40 year old boiler, but the price per therm is outrageous from my chair. I only own 2 homes on NG both through the same company, but it's $.72/therm. So like 1/4 the price of yours? That can't possibly be, can it? One of mine is about 1400 SF with 50s insulation and mostly single pane windows but the highest gas bill I've ever seen was $130
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Oh yes, @GroundUp . The price does seem high — but it's true. Welcome to New England.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
Looks like about a 50,000 btu /hour so I wouldn't think excessive for the square footage.
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Yes, you are leaking badly.
For comparison, I live in a 4-unit condo building in the Boston area, 4800 sq ft heated by oil. Building was built 100 years ago, first floor masonry, second floor frame construction. 10" cellulose in attic and a combination of new replacement windows plus original wood windows professionally weatherstripped, with storms.
In December we burned about 28 million BTU's for the entire building, which works out to about 5,900 BTU/sq ft.
In a similar period (a month) you say you burned 362 therms, or 36 million BTU's, which works out to about 19,000 BTU/sq ft.
So you are losing heat around 3x as fast as we are. Our "design" heat loss on a zero-degree day is just under 20 BTU/sq ft. So your "design" heat loss on the same day may be as much as 60 BTU/sq ft. That is very bad. That is like, living in a barn bad.
Despite your insulation, you probably have serious air leakage problems. Your old windows are the #1 suspect. They can be professionally weatherstripped with spring bronze and silicone rubber seals, after which (in combination with storm windows) they will be roughly on par with double-pane replacement windows.
We had that done with our original wood windows, at a cost of about $500 per window many years ago. There are several reputable professional window restorers who do this weatherstripping work in the Boston area who I can recommend if you want to PM me.
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Thanks for the insight! Almost all of the windows were replaced by the prior owner with dual pane, save the windows in the basement. That could definitely be a point of leakage.
We did do an energy assessment through Mass Save and did a bit of insulation work. Does it make sense to pay for another assessment of maybe higher caliber to help understand where the leaks are occurring?
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Yes, you really need a blower door test. If you have new windows and are still losing 60+ BTU/sq ft design heat loss, you probably have big air leaks somewhere else, and a blower door test will show you where. With air leaks that bad, insulation is useless because the heat loss via air leakage overwhelms any heat savings by insulation.
The cheaper method is to take a burning incense stick and go all around the house on a windy day, near windows, doors, electrical outlets, ceiling light fixtures, bathroom vent fan, foundation sill plate perimeter, and find where the smoke is blowing. That will give you a pretty good indication of where your problem areas are.
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This is great, thanks! When the insulation contractor was out last time they didn't recommend the blower test as they said it will disturb asbestos in the attic. Will try the burning incense stick method. Thanks again!
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Could it also be a problem with the boiler using gas inefficiently or the system not distributing water efficiently or something like that? Or is that unlikely
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What type of radiators do you have? Big old cast iron, or newer baseboard? Do all radiators get hot within 20 minutes after the boiler starts running?
If you have radiators that don't get hot, it's possible you have some hot water circulation problems, but at first look I still think your biggest problem is probably air infiltration.
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NG in the Boston area is now around $2.40/ therm.
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Big old cast iron. They do get pretty warm but not super hot.
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What is your boiler's BTU rating? It should be on a sticker or plate on the boiler.
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It's a Burnham Holiday burner with an input BTU of 210,000 and an output BTU of 168,000 (80% efficiency I guess?).
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When the thermostat calls for heat, how long does the boiler usually run until the thermostat is satisfied and shuts the boiler off?
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On Long Island, NationalGrid charges its residential customers 1.33/therm for supply and delivery.
My 12/6 - 1/6 bill for a 3,200 sq foot 1915 hollow clay tile masonry Colonial was $ 586 for 439 therms. On the ocean. Dunkirk steam boiler from 1974. 160K BTU Carlin G3B gas conversion.
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While you are looking for heat losses — be very suspicious of the fancy new windows. Poor installation can cause them to leak like sieves.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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During the day it'll turn on for 10 minutes and then shut off for 10-20 minutes and then repeat. Which, if my math is right, would loosely line up with the therm usage shown on the gas meter.
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What is the differential, or swing, setting on your thermostat? For your cast iron hot water radiators, it should be around 1.0 degrees, or more. If the thermostat swing is set improperly low (like for a hot air furnace) it will short cycle.
Also, do you have a domestic hot water coil in the boiler?
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According to the manufacturer, it is a 1.0 degree differential and this cannot be changed.
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I checked the thermostat and it was set to a cycle setting for a furnace and not a hot water system. We'll see how that changed setting works!
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I have a very similar old home (19XX SF, built 1920) in Rochester NY and keep a spreadsheet of all my usage going back to winter 2021-2022. My usage is similar to yours (months alternate between estimate and actual meter reads):
- 2021-2022
- November: 288
- December: 446
- January: 350
- February: 237
- March: 168
- Average: 298
- 2022-2023 (incomplete)
- November: 280
- December: 322
- January: 392
- Average: 331
- 2023-2024
- November 234
- December 268
- January 441
- February 317
- March 288
- Average: 310
- 2024-2025
- November 251
- December 361
- Average: 306
I keep my house at 68-72 and talking with others my heating bill is on the high end, but not massively so.
On top of that, using a Heating Degree Day Lookup, Rochester needed 400 more days than Boston or 8-10% more heating.
Like @GroundUp I pay around $0.70-$0.80/therm, so my bill isn't too bad.
So, taking into account, I heat to a higher temperature and have more heating to do, this post is a long way of saying I agree with those whose say gas usage is high. But it isn't that much higher!
Are you sure you aren't using more gas for other purposes in the winter? Longer showers (water heater), more home cooking (gas range), or laundry (dryer), fireplace, or generator?
0 - 2021-2022
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In cold weather like this, the boiler should probably be running about 30 minutes at a time if the thermostat differential is 1.0.
We had the same type of short cycling due to incorrect Tstat differential when I moved here. After I found and fixed the setting, the boiler ran longer cycles and the rads got hotter.
But fixing the short cycling didn't change our oil consumption much, so I think you may still have major heat loss problems with your building envelope.
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That many therms in that small of a place is way too much. Either the house leaks like a sieve or something is not running well. Oversized boiler that is short cycling is not helping things either.
Once you get the boiler cycles down, measure flue temperature just out of the boiler after at least a 1/2h burn (you can crank the thermostat for this). Your boiler might be sending a lot of heat up the pipe.
Is this a 1/2 story house? How cold is your basement in the winter? As for air leaks, the good news is most of those are in the DIY category. They take a lot of elbow grease but don't cost all that much in terms of materials.
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It's a 3 story house but the 3rd story is a semi-finished attic. I have closed the door to it and used a door sock to avoid having to heat that space. It's about 200 sqft that I didn't include above (so 2100sqft with that space, 1900 without).
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Bottom line is that, by comparison with my 100-year-old house in same metro area and well-documented heat loss of under 20 BTU/hr/sq ft, you could be losing 2x that or more.
We still don't know how much of that is due to boiler inefficiency, but it's hard to imagine the boiler running inefficiently enough to consume 2x the therms that it should. So I think most of your heat loss is probably due to bad air leaks.
If I were you, my goal would be to halve the heat loss, which would halve your heating cost. You may not get there, but it's a reasonable goal.
Unless you have some fundamental problem with your building envelope, that should be achievable, mainly with better air sealing, and then with better insulation.
You're spending so much $$ on wasted energy that I'd get one of these thermal imagers and go around the house with it (in addition to the incense stick). You're going to find a ton of dark blue cold spots that will show you where to do air sealing first, followed by insulation at a later time when you have the funds.
https://www.amazon.com/TOPDON-Handheld-Resolution-Infrared-Shutdown/dp/B0DJD2P3FF/ref=sr_1_3?crid=18LIFZ1O9WB49&dib=eyJ2IjoiMSJ9.7I4f4DS_j466drCPZYIRCiglkJxR71SF3m6RHGhvKuIhulFmRuYUdc0NCX3sEbNehITreofG_viT9xJQ6O2oowSxq_HdY2IEHm_jfhtJMfe6qqelm14HISgSPQ4AqIxc2Ev_KUKFp7hJUmiuphhHe6GEPsaLGb3BqCK2cJjs3APekFP7YiSsAzF6ALuUgSdL59WswWpkoGTxzSBqSTALPyM9wzg39fx59oJdicTGy7M.-zN3uLNxqyLbVRfSlgZCjAZqlg_d8afPL-tjyC6oDbU&dib_tag=se&keywords=thermal+imager&qid=1737067490&sprefix=%2Caps%2C1670&sr=8-3
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There are a couple drafty spots I need to fix and I do need to get some insulation in the attic. I may be limited on insulation options though as the walls apparently are of construction where they don't have room even for blown in insulation. I'll report back here later once I have more data. @jesmed1, really appreciate your help!
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Hi Karl, not to pile on here, but you might want to take a look at your air sealing and insulation too.
A quick look at the HDD's in Rochester for last month (December) shows virtually the same number of HDD's as at my local airport (Norwood, MA, weather station KOWD). Rochester: 955 HDD Norwood: 951 HDD.
So with almost identical therm usage and square footage, you are in the same boat as zallomallo.
You seem to be insulated from the pain by low gas prices, but if you were inclined to do some air sealing, it appears you may find some low-hanging fruit, as it were, with a lot of room for improvement at (hopefully) minimal cost if you do the work yourself.
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For sure on this - it also doesn’t help that I have three enclosed porches (one of which - the sleeping porch - is my master bedroom) and the extra heat loss from that. This was my plan for next year.
But, my December bill was an estimate - I do know it was lower as I read my meter after I got the bill and only then was it about where the estimated reading was. It’ll even out in February - that’s exactly why I posted multiple months.
On top of that, my Mother-in-Law is staying in my attics (see my posts for my inability to keep that space up to temperature and I am just plain energy inefficient at the moment.
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@zallomallo You don't have a couple of small drafts to fix, you have a whole bunch of them. Insulating is not the same as air sealing, you need to actively stop air from blowing through your house and installing a bunch of fluffy insulation will not do anything. Also if air is flowing through the insulation, its R value drops dramatically, so you have to get the air sealing done first before any insulation projects.
What you want is to get somebody that does blower directed air sealing. They usually have the equipment and expertise with these older buildings and know where to look for leaks.
You can also DIY with a budget thermal camera and a box fan. You put the box fan into one of your main floor windows blowing out and turn it on. You can than go around the house with the thermal camera to see where there are cold spots. You want to plug all those holes with either canned foam or pieces of rigid insulation sealed in place with foam. Seeing how much energy you use, you probably won't even need a thermal camera as you'll be able to feel the drafts. Make sure to turn off your boiler before you do any of this to avoid revers drafting it.
Typical trouble areas in these older houses are rim joist area of the main floor, leaky windows and framing cavities that are open to the attic.
For example my uninsulated stone basement was close to freezing even with the boiler and pipes running through it. Replaced the 100 year old single pane windows, air sealed the rim joist area and under the outside doors, fixed the brass weather stripping on the outside door and place now sits around 60F. I can now actually use it as a workshop year around.
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To refine your numbers a bit, using the following data for December in Boston:
362 therms used
951 HDD
1900 sq ft
That gives a boiler total input of 50 BTU/hr/sq ft at a design temp of 5 degrees, which is pretty close to my initial estimate of near 60 BTU/hr/sq ft by comparing your usage to ours in the same area.
However, this doesn't account for combustion inefficiency and the resulting lower BTU output of the boiler. If your boiler is, say, 80% efficient, then your actual heat loss through the envelope is more like 0.8 x 50 = 40 BTU/hr/sq ft. That's still 2x as bad is my old house, but it's not 3x as bad.
Then if you're also using gas in a separate water heater, maybe 15% of your gas bill is for DHW. So now your house is losing (100-15)*.8 = 68% of total therms as actual heat loss through the building envelope, or 34 BTU/hr/sq ft.
So it's not as bad as I first estimated, but you still have plenty of room for improvement.
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I did the Mass Save energy assessment and did their recommendations but it sounds like I need more. Can I just call them again and ask for a second assessment or should I just go out of pocket and get a pro to come airseal.
For DHW/the stove, my usage over the summer was 26 therms/month. I assume this would be closer to 40 now with the ambient water temp being much colder in the winter.0 -
Mass Save isn't going to tell you anything different the second time around.
What you really need first is air sealing, and you won't know where to focus without a blower door test. I know you said they wouldn't do one because of suspected asbestos in your attic (I assume old vermiculite) but there are people who will do a blower door test blowing in (positive pressure) instead of out (negative pressure). The positive pressure ensures asbestos is not drawn into the house.
Ask me how I know not to insulate before you do air sealing…we had 10" cellulose blown into our attic over the original thin layer of vermiculite (yes, you can do that—encapsulation) and I expected to see a 25% reduction in heat loss based on R-value calculations. In reality we only got less than 10% reduction. Disappointing. Why? Because we didn't do air sealing first, and air blowing through insulation drastically reduces its effectiveness. So we spent nearly $5k for very little benefit.
Here's a very informative blog from an energy professional explaining why some home energy efficiency projects fall short of expectations. Note that one of the key factors is air sealing the top plates in the attic. I wish I had known that before we did our attic insulation.
And here's an informative article about interpreting blower door test results:
https://www.finehomebuilding.com/project-guides/insulation/using-a-blower-door-test-and-interpreting-the-results
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Be very careful with air sealing and insulation. Diminishing returns are real and job can easily pay way more per therm than a therm costs.
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This is true. Nate Adams talks about this in the link I posted above. Doing too little may not get results, and doing too much may not have the ROI. You have to find the "sweet spot."
But starting with obvious air leaks that you can stop yourself is a low-cost first step that usually gets good results.
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