# Thread: calculate cost to heat or cool house

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I would agree they seem a little low, but beenthere usually knows what he's talking about.

As far as doing the calculation, the rates, and intervals are already accounted for, all you need to do is add that % to those total dollar numbers.

If he had 60 and you're saying 64, then its about 6.5% higher cost.

Take his 1200 dollar number, or whatever they were and add 6.5% (I think 6.25% to be exact.

So, take 1200*1.0625 = 1275. simple

Yes, the 64 is per hour, but if all those energy dollars given include all that based on 60 per hour, then its like saying, for every hour, its just 6.25% more, so overall, 6.25% more than the big number.

2. COP, although important. Has more effect on heat pumps with electric aux heat, then it does on dual fuel systems. That are locked out at a balance point that makes them switch to the more expensive heat source as sole source of heat.

Only redid two at a COP of 3.5

HP at an averaged COP of 2.5 providing 70%, elec Aux providing 30% = \$1,121.59
HP at an averaged COP of 3.5 providing 70%, elec Aux providing 30% = \$966.89
Difference of 14%.

HP at an averaged COP of 2.7 providing 55%, 94% LP providing 45% = \$1,268.11(LP hot air furnace)
HP at an averaged COP of 3.5 providing 55%, 94% LP providing 45% = \$1,180.87(LP hot air furnace)
Difference of 7%.

I picked a arbitrary total yearly house heat load of 60,000,000, just because its an easy number to work with, and representative of many mid sized homes.

I also picked arbitrary COP's because I don't have extended data on his equipment, and I don't know his weather pattern. So I choose a safe COP so as not to show an excessively false low operating cost.

You just wanted an idea of how long it would take to get the 25% additional cost back.
If you know what your total heating fuel use was for last year. You can use that with my numbers to get a fairly accurate idea of ROI time. Just by doing the percents.

For sizing purposes, heat loss and gain are calculated by the hour.

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Originally Posted by beenthere
COP, although important. Has more effect on heat pumps with electric aux heat, then it does on dual fuel systems. That are locked out at a balance point that makes them switch to the more expensive heat source as sole source of heat.

Only redid two at a COP of 3.5

HP at an averaged COP of 2.5 providing 70%, elec Aux providing 30% = \$1,121.59
HP at an averaged COP of 3.5 providing 70%, elec Aux providing 30% = \$966.89
Difference of 14%.

HP at an averaged COP of 2.7 providing 55%, 94% LP providing 45% = \$1,268.11(LP hot air furnace)
HP at an averaged COP of 3.5 providing 55%, 94% LP providing 45% = \$1,180.87(LP hot air furnace)
Difference of 7%.

I picked a arbitrary total yearly house heat load of 60,000,000, just because its an easy number to work with, and representative of many mid sized homes.

I also picked arbitrary COP's because I don't have extended data on his equipment, and I don't know his weather pattern. So I choose a safe COP so as not to show an excessively false low operating cost.

You just wanted an idea of how long it would take to get the 25% additional cost back.
If you know what your total heating fuel use was for last year. You can use that with my numbers to get a fairly accurate idea of ROI time. Just by doing the percents.

For sizing purposes, heat loss and gain are calculated by the hour.

Beenthere - thanks for your the information.

Can i calculate my seasonal heat load from the heat load ( 64K BTU/Hr) and heating degree days (4808). If not what do i need to calculate it

Thanks

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Originally Posted by doogan123
Beenthere - thanks for your the information.

Can i calculate my seasonal heat load from the heat load ( 64K BTU/Hr) and heating degree days (4808). If not what do i need to calculate it

Thanks
Do you have any historical fuel usage? A years worth of fuel (in btus) multiplied by the existing system efficiency will yield the annual heat load. The wild card is the existing equipment efficiencey - may be hard to get that number right on. But you can get pretty close - a standard efficiency boiler or furnace might be 78&#37; or so...

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Unfortunatly I do not - I had an ancient system that sucked in fuel and shot it up the chimney.

probabally 1500-200- Gallons of Oil if i would guess..

My boiler was .. 50-60 years old - a real gem.

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Originally Posted by doogan123
Unfortunatly I do not - I had an ancient system that sucked in fuel and shot it up the chimney.

probabally 1500-200- Gallons of Oil if i would guess..
So account for the "shot it up the chimney" by adjusting the overall system efficieny.

Here's an example - play with the numbers as you like.

(2000 gal / yr) (139,000 btu / gal) (65% overall efficiency) = 180,700,000 btu / yr.

Seems highish - domestic hot water also oil fired?

7. Originally Posted by doogan123
Beenthere - thanks for your the information.

Can i calculate my seasonal heat load from the heat load ( 64K BTU/Hr) and heating degree days (4808). If not what do i need to calculate it

Thanks
Best way is using the bin data.
What major cities are you near.
I may have the bins for it.

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ENERGYSTAR.gov > heatpump calculation

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Danbury, Ct (Closest)
White plains
NYC

Any of these ring a bell?

Also - I found a spreadsheet on here - heating_cost_calculator_region_v. One of the fields is HCOP and its defined as a percentage. I have the COP of the potiential heatpumps - what is the relationship of COP to HCOP (Number Vs Percentage) How do i convert one to the other?

I think this spreadsheet might do what i am looking for if I could figure this out and the seasonal BTU's

thanks

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Originally Posted by larobj63
So account for the "shot it up the chimney" by adjusting the overall system efficieny.

Here's an example - play with the numbers as you like.

(2000 gal / yr) (139,000 btu / gal) (65% overall efficiency) = 180,700,000 btu / yr.

Seems highish - domestic hot water also oil fired?
Yes - domestic was oil fired also. I filled a 500 gallon tank around 4 times a year. My old house was not really insulated, terrible windows, etc. maybe 2000 is a little high - not much tho. I did not keep records (Thats changing)

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Originally Posted by doogan123
Yes - domestic was oil fired also. I filled a 500 gallon tank around 4 times a year. My old house was not really insulated, terrible windows, etc. maybe 2000 is a little high - not much tho. I did not keep records (Thats changing)
Are you sure you have a 500 gallon tank? 99.9&#37; of em out there are 275's...

But I guess you would know - you paid for the black gold.

DHW heating is a significant part of the picture. Depending on your usage, it's likey 200 gal / yr at least.

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Originally Posted by larobj63
Are you sure you have a 500 gallon tank? 99.9% of em out there are 275's...

But I guess you would know - you paid for the black gold.

DHW heating is a significant part of the picture. Depending on your usage, it's likey 200 gal / yr at least.
Yep - sure.. BIG.. BLACK.. ROUND.. STEEL.. TIED WITH a CHAIN UNDER MY PORCH.. NOW NICELY DISPOSED OF....

13. New York City.

0to5 1hr, 5to10 10hrs, 10to15 26hrs, 15to20 2hrs, 20to25 188hrs, 25to30 330hrs, 30to35 603hrs, 35to40 858hrs, 40to45 838hrs, 45to50 796hrs, 50to55 722hrs, 55to60 745hrs, 60to65 754hrs.

I come up with 145,358,147 Total yearly heating BTUs.
Presuming you set your stat at 70°F.

Its 4009 more if you use your heat when its 68 outside.

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