Heating cost - Gas hydronic vs Heat Pump Split for addition

Steve Garson_2

We all have read about modern heat pumps being 200% efficient. I was running some numbers comparing the cost versus gas, since we are adding a new room to our house, which is heated with a 90% efficient gas hydronic boiler.

Please tell me if my logic is correct:

Gas cost in Denver: $1.32/therm = 100,000 BTU
Electric cost in Denver: $0.143 per kwh

29.3 kwh = 100,000 BTU at 100% efficency
If heat pump is 200% efficient, that's 14.65 kwh = $2.095/100,000 BTU

Gas heating cost at 90% efficiency: $1.32 x 100,000/90,000 = $1.46

Therefore, heating with gas costs 30% less (corrected). Based on present energy costs.

Is my logic correct?

Steve

Jamie Hall

Yes

Hot_water_fan

That’s the correct calculation, right up until the end: 1-1.46/2.10 = 30% cheaper. My COP is about 3, which would make the heat pump cheaper. These prices change all the time, so don’t sweat the small differences. Does your addition want AC? That’s the real kicker. 

HomerJSmith

One must factor in all costs over time, not just usage costs. Usually costs of an agenda are only expressed that make that agenda look good. Real costs are suppressed. A lot like the CPI (consumer price index).

pecmsg

What do you have currently for heat?
furnace, HW Radiators, Steam?

Hot_water_fan

@HomerJSmith no politics on the wall please. 

HomerJSmith

Hot_water_fan, that ain't politics that's Economics, there is a difference.
Economics: noun
(used with a singular verb) the science that deals with the production, distribution, and consumption of goods and services, or the material welfare of humankind.

Hot_water_fan

I suppose economic agendas could be apolitical. No problem with me then. 

Steve Garson_2

Using baseboard hydronic in rest of house. Was planning to do the same in new room with heat pump for AC. Then decided that I should just install the heat pump to avoid the cost of extending plumbing to the new room for baseboard.

Hot_water_fan

@Steve Garson_2 yup that’s usually the kicker: pay about the same for heat, but get AC and save the baseboard parts and installation. For an addition, your additional annual heat cost should be low! 

Steamhead

The HP would give you some redundancy. But I'd still do HWBB for its superior comfort as compared to the HP.

pecmsg

Heat pumps do a good job but I still wouldn’t use them as primary heat. When it’s cold and windy you’ll want that HW Radiator. 

Jamie Hall

Folks, we don't know where this is located. It makes a difference. In some more southern areas, a heat pump is fine for all your heating needs, with a/c as a benefit. Further south, a heat pump is fine for all your a/c, with heat as a benefit. Where I am located, a heat pump is fine for heat in the shoulder seasons, but goes paws up on a cold day when the steam takes over. A/C is needed maybe two days a year.

So... where is this?

Hot_water_fan

@Jamie Hall the location is Denver, based on the original post. The OP wants AC too. 

Steve Garson_2

My heat pump was fine to minus 5.  The two nights it hit minus 10 when my boiler failed, 65 was the best I could do, which actually amazed me.  Was glad for redundancy.

pecmsg

Steve Garson_2 said:

My heat pump was fine to minus 5.  The two nights it hit minus 10 when my boiler failed, 65 was the best I could do, which actually amazed me.  Was glad for redundancy.

Exactly!

Jamie Hall

Might get away with just a heat pump then. There will be a few days each winter when it won't make it happen, but -- some folks don't mind.

The Steam Whisperer

Steve Garson_2 said:

We all have read about modern heat pumps being 200% efficient. I was running some numbers comparing the cost versus gas, since we are adding a new room to our house, which is heated with a 90% efficient gas hydronic boiler.

Please tell me if my logic is correct:

Gas cost in Denver: $1.32/therm = 100,000 BTU
Electric cost in Denver: $0.143 per kwh

29.3 kwh = 100,000 BTU at 100% efficency
If heat pump is 200% efficient, that's 14.65 kwh = $2.095/100,000 BTU

Gas heating cost at 90% efficiency: $1.32 x 100,000/90,000 = $1.46

Therefore, heating with gas costs 30% less (corrected). Based on present energy costs.

Is my logic correct?

Steve

You left a piece out of your pricing.... Your gas boiler is also using electricity and that cost needs to be figured in. "High Efficiency" boilers tends to use large amounts of electricity compared to "standard efficiency" boilers, so your electricity usage over a heating season can add up. Being as cold as Denver is, I could see your COP being near 2 instead of 3.0 in much warmer climates. The other factor is when is Denver going to start running out of electricity in cold snaps... About 3/4 of the U.S. population is already there... as demonstrated this last Christmas. I would certainly want a back up for weather extremes going forward.