EcoRenovator - View Single Post - Heat pump water heater intake from hot attic

Servicetech · 05-22-16, 07:54 AM

There are 29.3KWH in a therm of gas. 29.3 x.11 cents per KWH (do you stay under 600KWH most months?, most people don’t) = $3.22 Gas is 44 cents, you need a COP of 3.22/.44 = 7.3 for the HPWH to make sense. Most tank water heaters get about 78% THERMAL efficiency, which means you need a net COP of 5.85 to make sense.

Odds are the bosch tankless is NOT modulating, which makes temp control difficult. Fine for a cabin or a single person, but it ain’t gonna fly if you have a family.

Sad to say, but the plain boring NG tank is probably your best option. Natural gas is cheap, it doesn't cost THAT much to heat water to begin with...

05-22-16, 07:54 AM	#8
Servicetech Apprentice EcoRenovator Join Date: Nov 2013 Location: Moore Oklahoma Posts: 267 Thanks: 108 Thanked 23 Times in 21 Posts	There are 29.3KWH in a therm of gas. 29.3 x.11 cents per KWH (do you stay under 600KWH most months?, most people don’t) = $3.22 Gas is 44 cents, you need a COP of 3.22/.44 = 7.3 for the HPWH to make sense. Most tank water heaters get about 78% THERMAL efficiency, which means you need a net COP of 5.85 to make sense. Odds are the bosch tankless is NOT modulating, which makes temp control difficult. Fine for a cabin or a single person, but it ain’t gonna fly if you have a family. Sad to say, but the plain boring NG tank is probably your best option. Natural gas is cheap, it doesn't cost THAT much to heat water to begin with...