Heat Pump vs. Furnace energy usage 2024-2025 results

Hot_water_fan

I've posted this a few times now and wanted to update with 2024-2025 numbers.

My house was heated by a furnace for 110 days in 2020-2021, then replaced with a ducted heat pump. Here are the therms and kwhs used for that time period during the furnace period and the following years. A few notes:

• Historically, this Nov. - mid Feb period is about 2/3rds of the 11/1-10/31 period's heating degree days. It's also the coldest 2/3rds.
• In 2023, the gas water heater was replaced with electric resistance, which explains the therms reduction starting in the 11/1/2023-2/28/24 period. That adds roughly 1000 kwh to the electricity usage for the time period (57.5 therms x 60% efficiency x 100,000 btus/therm / 3412 btus/kwh = 1010 kwh).
• The main change for the 11/1/24-2/18/25 period was switching to a time of use rate. I expected to lose some efficiency in exchange for decreased costs, it seems to have worked out. The TOU rates save me more in the summer, so that's the main reason I will continue to use them.
• I've got regressions to determine fuel usage per heating degree day:
  • Gas coefficient: .11 therms/heating degree day
  • HP coefficient: 1.22 kwh/heating degree day
• Current $/therm gas rates (Feb bill):
  • Supply rates: $.623
  • Distribution: $1.0055
  • Empower MD: $.1087
  • Tax: $.039831
  • Total: $1.77/therm
• Current $/kwh rates (Feb Bill) (On peak was 13% of usage)
  • On Peak/Off peak:
    • Supply: $.24324/kwh / $.08198/kwh
    • Distribution: $.11714/kwh / $.03426/kwh
  • Charges the same for both
    • Empower MD: $.01028/kwh
    • Franchise Tax: $.00062/kwh
    • Local Tax: $.003356/kwh
    • Envir Surcharge: $.00015/kwh
  • Weighted Average for Feb bill: $.1604/kwh

		Heating Degree Days 60
Start	End	Total	Max	Average	kwh	therms
11/1/20	2/18/21	2,092	32	19	1,417	295
11/1/21	2/18/22	2,129	38	19	3,304	58
11/1/22	2/18/23	1,826	47	17	3,231	66
11/1/23	2/18/24	1,929	40	18	3,978	4
11/1/24	2/18/25	2,284	45	21	4,739	5

jesmed1

So comparing your heating cost at current rates for the two different fuels:

Gas: 0.11 therm/HDD x $1.77/therm = $0.195/HDD

Heat pump: 1.22 kWh/HDD x $0.16/kWh = $0.195/HDD

So your heating costs turn out to be the same for the different fuels. Obviously the comparison will be different for other owners in different zones, with different COP's and different rate structures.

I had been considering switching our oil boilers here in the Boston area to gas, but with this winter's gas rate hikes, I'm glad that plan didn't work out.

I had also been looking at air-to-water heat pumps with a heat exchanger for our existing hot water heating system with old cast iron radiators, but the conversion would have been so expensive and the benefits so modest that the payback period would have been around 50 years…not feasible.

Hot_water_fan

Yup everyone’s mileage will vary. Our gas supply costs vary widely - between $.25 and $1.10 per therm over the last three years.

The next step for savings is ditching the gas stove. That’ll save me almost nothing energy wise but will save me $180 a year in fixed costs.

ethicalpaul

Induction is so good. Faster than gas, no combustion gases, and it will shut off a burner element after awhile if there's nothing on it, or if the water all boils out of whatever's in the pan.

Hot_water_fan

@ethicalpaul don’t have to convince me! Just waiting for the right time.

KarlW

With @jesmed1's anaylsis It appears you did revealed a rough ratio of gas versus KWh. If a therm of natural gas is less than 10x a KWh, then a heat pump is economical to operate.

But, that's some expensive natural gas! In Western NY, I'm at $0.85/therm. I pay around $0.18/kwh for electric. So for me, natural gas is a lot cheaper.

jesmed1

@KarlW LOL. Here in Boston, electric is 2x your cost, and gas is 3x!

EBEBRATT-Ed

Welcome to the State of Massachusetts. They want to get rid of gas.

Hot_water_fan

@KarlW A ratio of 10 is pretty good as a rule of thumb. It's basically saying COP = 2.8 for heat pump vs. COP = .95 for gas. Both are reasonable.

Our gas is cheap enough. Our gas pipes are expensive and they're still leaking! Can't see that cost going down any time soon unless they really start optimizing the gas grid. That might mean cutting some homes off or charging them closer to their actual cost.

Hot_water_fan

@EBEBRATT-Ed In MD, the gas utility is digging their own grave more than the state is. The grid cost is just too high to keep going.

KarlW

https://forum.heatinghelp.com/discussion/comment/1844802#Comment_1844802

As if New York doesn't!