3 ms·

I've been using two heat pumps near Austin, Texas since 2011, rated at a total of 84,000 BTU/hr (4 ton + 3 ton capacity) (25KW of heat) on a total of 5KW electr

I've been using two heat pumps near Austin, Texas since 2011, rated at a total of 84,000 BTU/hr (4 ton + 3 ton capacity) (25KW of heat) on a total of 5KW electrical input (COP ~= 5.0). They are standard outdoor air heat exchangers so below about 35F efficiency drops significantly. That's pretty rare around here so it is almost always enough - we can still gain about 45F vs the outdoor temperature even below 20F. We don't have natural gas available where I live, only propane. When I purchased the heat pumps, propane was $5/gallon for 91,500 BTU. That translates to about $4.60/hr to run 84,000 BTU/hr of furnace. With electric energy (cheap in Texas!) at about $0.11/KWh, the equivalent costs of my heat pumps was and remains close to about $0.55/hr to run. In the summer, they cool with equal capacity and similar power consumption for a 15 SEER rating (waste heat from the system components works against cooling in the summer!) Factor in your acquisition costs (mine, just after the housing bust and with a little legwork, were about 20% of retail at the time, so a no-brainer) and you can get a lot more objective idea what you're really accomplishing.

lm28469 8mo ago
> I've been using two heat pumps near Austin... (25KW of heat) Is this for a single house? What kind of insulation do you have
- bob1029 8mo ago
  For ATX, this capacity is entirely about the summer. Any winter performance is an afterthought.
  - OldSchool 8mo ago
    That's for sure. It can get pretty hot and humid, not quite Houston-like but you spend some significant cooling capacity condensing water out of the indoor air as well.
  - lm28469 8mo ago
    Insulation works regardless of the climate though. A well insulated house will be much easier to cool down in Texas, and much easier to warm up in Alaska
- OldSchool 8mo ago
  I hear you, it's a single two-story house built in 2000, not small but smaller than typical developers build these days here. I added 18 inches of insulation to the attic, not much I can do in the walls. Double-pane glass. It's not drafty but seems poorly insulated as a whole despite being relatively modern and better-than-average quality. Houses in cold climates seem much tighter and better insulated.

lm28469 8mo ago

> I've been using two heat pumps near Austin... (25KW of heat) Is this for a single house? What kind of insulation do you have

bob1029 8mo ago
For ATX, this capacity is entirely about the summer. Any winter performance is an afterthought.
- OldSchool 8mo ago
  That's for sure. It can get pretty hot and humid, not quite Houston-like but you spend some significant cooling capacity condensing water out of the indoor air as well.
- lm28469 8mo ago
  Insulation works regardless of the climate though. A well insulated house will be much easier to cool down in Texas, and much easier to warm up in Alaska
OldSchool 8mo ago
I hear you, it's a single two-story house built in 2000, not small but smaller than typical developers build these days here. I added 18 inches of insulation to the attic, not much I can do in the walls. Double-pane glass. It's not drafty but seems poorly insulated as a whole despite being relatively modern and better-than-average quality. Houses in cold climates seem much tighter and better insulated.