4 ms·

Also in NYC. I pay roughly 35cents per kWH (air-source heat pump) and $3 per therm natural gas (radiant heat, 95% efficient). I think 1 therm == 100k BTU, 1kWH

Also in NYC. I pay roughly 35cents per kWH (air-source heat pump) and $3 per therm natural gas (radiant heat, 95% efficient). I think 1 therm == 100k BTU, 1kWH == 3412 BTU. To equal 1 therm is takes 29kWH of electric heat costing $10.15. Then divide by the efficiency of heat pumps: $3.40 at 300% efficiency, $5 at 200%. I’ve read air-source heat pumps become far less efficient as the temps fall, so < 2x may be more realistic in winter.

crmd 4y ago
Hey, thanks for responding. Am I understanding you correctly that 1 unit of gas heat costs $3 and each unit of heat pump heat costs between $3.40 and $5.00 depending on efficiency of the heat pump?
- silverlake 4y ago
  If my math checks out (which is doubtful) then yes, heat pump could be more expensive than gas heat on the worst cold days like last week (10F). However, a heat pump handles heating and cooling. So it’s cheaper to install 1 system that does everything rather than 2 systems to save money on a few cold days. Add a few solar panels and the heat pump cost goes to 0. However, we put in a gas combi-boiler for hot water. Since we were renovating a townhouse, it was easy to throw in some radiant heaters on all floors. It’s a quiet, comfortable heat. I have the heat pump set to assist if the temps drop below 68F inside. All that said, insulation and air sealing is by far the most important thing to do first. FYI: I checked the specs on my unit. It claims a 3.3X COP. So that’s $3 per therm, same as gas.
mechagodzilla 4y ago
NYC’s design temp is like 17F or something, so the seasonal average COP is probably above 3 for good cold climate heat pumps.
dgacmu 4y ago
The 300% is closer to an average. When it's over 40F you'll reach over 400% efficiency. Now a question to address is whether your radiant heat is actually getting 95% efficiency. If you have an old radiator design system that was converted to using a condensing boiler, it may not be designed to keep return temperatures low enough for the boiler to operate at maximal efficiency. (old boiler systems were designed to keep the return water supply hot to prevent acidic condensate from eating the heat exchanger. This is the exact opposite of what you want with a modern system, where the return water needs to be cold enough that the flu gases condense into it to recover heat.) If you have a way to monitor the return water temperature into your boiler, you could check. You need the return water to be below about 100 Fahrenheit in order to have 95% efficiency.

crmd 4y ago

Hey, thanks for responding. Am I understanding you correctly that 1 unit of gas heat costs $3 and each unit of heat pump heat costs between $3.40 and $5.00 depending on efficiency of the heat pump?

silverlake 4y ago
If my math checks out (which is doubtful) then yes, heat pump could be more expensive than gas heat on the worst cold days like last week (10F). However, a heat pump handles heating and cooling. So it’s cheaper to install 1 system that does everything rather than 2 systems to save money on a few cold days. Add a few solar panels and the heat pump cost goes to 0. However, we put in a gas combi-boiler for hot water. Since we were renovating a townhouse, it was easy to throw in some radiant heaters on all floors. It’s a quiet, comfortable heat. I have the heat pump set to assist if the temps drop below 68F inside. All that said, insulation and air sealing is by far the most important thing to do first. FYI: I checked the specs on my unit. It claims a 3.3X COP. So that’s $3 per therm, same as gas.

mechagodzilla 4y ago

NYC’s design temp is like 17F or something, so the seasonal average COP is probably above 3 for good cold climate heat pumps.

dgacmu 4y ago

The 300% is closer to an average. When it's over 40F you'll reach over 400% efficiency. Now a question to address is whether your radiant heat is actually getting 95% efficiency. If you have an old radiator design system that was converted to using a condensing boiler, it may not be designed to keep return temperatures low enough for the boiler to operate at maximal efficiency. (old boiler systems were designed to keep the return water supply hot to prevent acidic condensate from eating the heat exchanger. This is the exact opposite of what you want with a modern system, where the return water needs to be cold enough that the flu gases condense into it to recover heat.) If you have a way to monitor the return water temperature into your boiler, you could check. You need the return water to be below about 100 Fahrenheit in order to have 95% efficiency.