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# Annual heating cost calculations

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Member Posts: 20
I understand that prices are not discussed on this forum. Please forgive me if I make a mistake and someone let me know. I wont add in any prices that I pay for heating oil. I just would like to see if I'm way off base with estimating my annual heating costs based on degree days.

Does the following look about right?

1) Calculated home heat loss of 75,000 BTU/hr for an indoor temp vs outdoor temp delta of 75 degrees.

2) This implies 1,000 BTU/hr heat loss for every 1 degree delta between indoor temp and outdoor temp or 24,000 BTU/day.

3) Assuming base 70 HDD of 6800 for the entire season this works out to 163.2 million BTU / season.

4) Assuming oil boiler efficiency of 78% the actual input needed would be 163.2/0.78 -> 209.2 million BTU / season

5) 209.2 million BTU per season / 140,000 BTU/gal #2 heating oil -> approx 1495 gal #2 heating oil per season

6) 1494 gals #2 heating oil * (whatever price I pay on average) -> my estimated costs per winter on average?

Is this correct? This seems way off. Where did I go wrong?

• Member Posts: 8,578
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Is your delta temp a constant 75 degrees, for the whole season?—NBC
• Member Posts: 23,442
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Well your logic looks reasonable. I don't know where you are, but 6800 degree days looks a bit high to me, but other than that I don't see much of a problem with it. Proof comes at the end of the year when you add it up!
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 85
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Your math is right, but some of your assumptions could be rethought.

HDD are usually base 65 deg F. Your home will create waste heat to heat the house some. Therefore, I would not assume an indoor/outdoor delta temp of 75 degrees. I would use 65 degrees. That means your total calculation goes down by the ratio of 65/75, or down to ~181 MBTUs or ~1300 gallons of oil.

But still, unless you have a big, leaky house with lots of windows, I would be surprised to hear you have 75,000 BTU/hr heat loss.
• Member Posts: 6,505
edited November 2019
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To the OP, what problem are you trying to solve?
Are you buying a house with oil and are wondering how much it will cost to heat your home?
New triple pass or EK, the efficiency (for this exercise) would be higher than 78%

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• Member Posts: 20
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The problem is as follows:

I maintain my parents home in the Northeast for them while they have retired down to the South. They didn't keep records of how much they paid for heating oil during the years.

They are now freaking out thinking that I have the heat seat to high in the house, because there is no way heating oil can cost that much for an 1800 sq ft house.

I'm trying to do some math to justify to them that, no, indeed, it does cost that much to heat your house in the Northeast winters!

What is ballpark reasonable for an 1800 sq ft home built in '86 w/ a 78% efficiency boiler and thermostats set to 68? Just ballpark estimates here would help me.

Meanwhile, I set the Aquastat to 160 HI, 140 LO, 10 LO DIFF because the DHW coil has been deleted years ago and isn't used and I see this as my "poor man's outdoor reset". People have said that running 180 deg water is more efficient and that by running 160 I am going to end up using more fuel to heat the home and that I should leave it at 180.

If that were the case, then how do people save fuel at all using outdoor reset controllers? 3/4 finned baseboard puts out around 400 BTU/hr vs 600 BTU/hr at 160 deg vs 180 deg. So, my heating cycles will take longer - but the boiler is oversized for the home heat loss anyway. So this will help with short cycling. But longer heat cycles -> more fuel burned than before.... This is where I get confused on how a lower boiler temp saves fuel.

Anyway....I hope setting those Aquastat temps down is going to save me fuel somehow !! Sadly I don't have records as to past fuel usage to compare to, to see if my settings improve the situation or make it worse.
• Member Posts: 23,442
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Chortle. My daughter and I have a client who sings exactly the same song, while she relaxes in sunny California...

To answer the question, though -- the cost of heating varies so much with the details of construction of a building. Therefore, any answer I could give you should be taken with great caution.

That said, I have records dating back for two decades on the main place I care for. It is an old building (build dates 1780 to 1893) and poorly insulated, to put it mildlym in the hills of northwestern Connecticut. It is kept at 65 F in the winter. It has about 7,000 square feet of heated area on three floors. Last winter the place used just over 3400 gallons of number 2.

I hope that helps...
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 23,442
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Quoting a price would be very difficult. It depends so much on the construction of the building and just where it is...

That said, I have records going back a couple of decades on the main place I care for. 7,000 heated space on 3 floors, very old (1780 to 1893) and poorly insulated, if at all, in northwestern Connecticut. It uses about 3500 gallons of oil a year.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 2,766
edited November 2019
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This actually works . Base temp should be the outdoor temp at which a building starts to require heat . Use this for your average HDD from the nearest location to your building . https://www.degreedays.net/
You didn't get what you didn't pay for and it will never be what you thought it would .
Langans Plumbing & Heating LLC
732-751-1560
Serving most of New Jersey, Eastern Pa .
Consultation, Design & Installation anywhere
Rich McGrath 732-581-3833
• Member Posts: 2,646
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Here in the far north...east, an unoccupied home set to 50F of that approx size should use about 800 gallons or less.

You figure of 75,000 btu/hr seems quite high to me, but I dont know where its located or the type of construction. Most average homes are under 60,000 btu/hr of that size, and that is here with a -40F design temp.
Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
• Member Posts: 6,505
edited November 2019
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Is the house both vacant & empty?
An empty house will use more fuel.
You shouldn't need a low limit, otherwise that boiler will maintain at least 140° year round. Unless the low limit was disabled and it's only turning off the circulator when it's below 140° water temperature. I'd turn the high limit down to 160°. Keep in mind, you don't know unless you test if that is even reading/responding correctly.
If there is no fear of pipe freezing, I would turn the thermostat down to 60°. Walk around the basement, near windows especially, and see what temperature you read. If it's staying above 40°, I'd leave it there, or even turn it down a little lower and keep testing.
You obviously don't want a frozen pipe, so don't go too low.
If they only used one oil supplier, they would have historical records.

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• Member Posts: 2,646
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Are you in close proximity to this house?
Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
• Member Posts: 20
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I am in fact in very close proximity to this house...so close in fact, that I live in it !

I have the thermostats set down to 68. I set the HI LIMIT on the Aquastat to 160 from the original 180 as my poor man's outdoor reset. I really wish I knew if this was going to actually save fuel.

I left the LO LIMIT at 140 so as not to run into condensation problems. I don't want lukewarm starts in the shoulder seasons.

The LO DIFF I have set at 10, because without a DHW coil, I don't see why I should have the boiler heat water higher than 140 in standby, however heating only 8-10 gallons in the heat exchanger by 10 degrees isn't going to take a 120,000 BTU unit very long. Maybe I should set it higher to reduce short cycling in standby?

I'd really like to pick up a Hydrolevel 3250 and let it handle everything.
• Member Posts: 20
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I guess heating a home in Connecticut is just darn expensive...

The parents did use a certain supplier for I think most of the 30 years they lived here. I wonder if I call and request records if they could/would furnish that information? Do they have any obligation to if I'm no longer a customer?

Thanks everyone for all your information and suggestions!
• Member Posts: 20
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Hey Rich_49, I plugged in some numbers using that Taco webinar you sent (great by the way), and came out with about 750 gallons of fuel usage on average per season.

Can you guys all from experience verify that leaving the Aquastat set at 160 vs 180 is going to actually not going to make me use more fuel since my rads are now only putting out 400 BTUs/hr vs 600 BTUs/hr ? The burner runs longer now...more fuel...I still dont get this idea. I don't have the experience to know how it's going to work out after 7 months. I'd rather leave it at 180 and use 750 gallons than leave it at 160 and use 1000 gallons or something silly !!

That would be a costly turn of a little red knob....
• Member Posts: 2,646
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Turning down the boiler temp will save a bit of fuel, how much....a bit. This is due to lower stack temps and slightly better heat transfer. If 160 heats the house then leave it there. It all depends on how much radiation you have and what type.

So you are living there, and they heated it for 30 years, but are now complaining that it costs too much? Oil is cheaper now that a few years ago!
Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
• Member Posts: 20
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They are complaining now because they retired to warm South Carolina !

They used to keep it at 72 as well !! LOL

It's OK. I just needed some solid information to prove to them that 700-800 gallons a season or so isn't abnormal.

I wonder how they felt in the 90s when #2 was at \$3/gal or higher?

They weren't the record keeping types...