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Old 04-18-2019, 04:41 PM   #1
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Heat Pump Best Option?


My BIL is looking at a house in San Jose...it has the typical gas wall heater....usually in the hallway and is 'supposed' to heat the whole house. The AC is a single window unit in the main room.

He is asking me about what it would cost to put in AC. I suggested maybe a heat pump so he can handle both heating an cooling...

But....maybe he is better off with a traditional forced air gas heating with external condensor?
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Old 04-18-2019, 05:55 PM   #2
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Re: Heat Pump Best Option?


If there's no conditioned space to run air ducts in he should look into a mini-split system with multiple heads. The wall-furnace gets kept for emergencies.

He should stay away from getting ducts put in an unconditioned space. Some say "it's fine - done all the time", in reality there's no way to avoid major losses putting 55 degree air through a 110F+ attic and putting 120F air through a cold attic or crawlspace.

The equipment may be more money installed but there are savings on air ducts as well as operating costs.

The mini-splits are the most advanced heatpumps out there - variable capacity compressor with extra capacity to maintain full heat output at very low outdoor temperatures.

Most central air style heatpumps have heating capacity drop off rapidly as it gets colder outside. Between 20 and 40F outdoor in most cases they need supplemental heat, usually electric, cutting into savings.

Whether to base a heating system around gas furnace or electric heatpump depends on local utility rates, climate, construction quality and whether running ducts is practical.
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Last edited by user_12345a; 04-18-2019 at 06:02 PM.
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Old 04-18-2019, 06:12 PM   #3
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Re: Heat Pump Best Option?


Quote:
Originally Posted by user_12345a View Post
If there's no conditioned space to run air ducts in he should look into a mini-split system with multiple heads. The wall-furnace gets kept for emergencies.

He should stay away from getting ducts put in an unconditioned space. Some say "it's fine - done all the time", in reality there's no way to avoid major losses putting 55 degree air through a 110F+ attic and putting 120F air through a cold attic or crawlspace.

The equipment may be more money installed but there are savings on air ducts as well as operating costs.

The mini-splits are the most advanced heatpumps out there - variable capacity compressor with extra capacity to maintain full heat output at very low outdoor temperatures.

Most central air style heatpumps have heating capacity drop off rapidly as it gets colder outside. Between 20 and 40F outdoor in most cases they need supplemental heat, usually electric, cutting into savings.

Whether to base a heating system around gas furnace or electric heatpump depends on local utility rates, climate, construction quality and whether running ducts is practical.
I should have pointed out, this is San Jose, California....not real cold....warm....but more humid in the summer
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Old 04-18-2019, 06:19 PM   #4
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Re: Heat Pump Best Option?


Is there a basement? Is it a bungalow or two-story?

A basement or crawlspace can be fairly easily insulated/conditioned, making it good for air ducts.

There are ways to insulate attic roof deck, turn attic into interior space, but likely lots of $$$.

Gas furnace is probably overkill for that climate. Heatpumps provide less heat than furnaces (meaning less cycling on and off especially with variable capacity mini-split) and run very efficiently in mild weather, supplying 3-4+ kwh of heat per kwh of electric consumed.

Gas may be cheaper in california than electric, but have to consider the cost of having a meter.

Layout needs to be consider - like if the house has many small rooms minisplit may not be practical.
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Old 04-19-2019, 06:09 AM   #5
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Re: Heat Pump Best Option?


What's his gas rate, and what's his electric rate?


If it seldom gets below 40 in the winter, probably doesn't really need aux heat.
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Old 04-19-2019, 07:32 AM   #6
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Re: Heat Pump Best Option?


Plus one for the minisplit with multiple heads. You'll probably want the ceiling cassettes, as they are less intrusive, and have better draining options then the wall hung versions, but are a bit more expensive.

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Old 04-19-2019, 05:42 PM   #7
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Re: Heat Pump Best Option?


Nothing's better than gas heat and I would stick with the gas furnace. If you can make it all one unit central heating cooling that's the way to go. Mini Splits I only recommend them if it's no other option. Mini splits very expensive install and very expensive to fix when they break.

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Old 04-20-2019, 12:38 AM   #8
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Re: Heat Pump Best Option?


Quote:
Originally Posted by thekux View Post
Nothing's better than gas heat and I would stick with the gas furnace. If you can make it all one unit central heating cooling that's the way to go. Mini Splits I only recommend them if it's no other option. Mini splits very expensive install and very expensive to fix when they break.

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Old 04-22-2019, 08:50 PM   #9
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Re: Heat Pump Best Option?


Sounds like its a post war (WWII), three bedroom, single level, tract house? (Probably worth over a million.........) If so, a force air system with a heat pump or gas furnace/AC with traditional ducts would probably work best (minisplits work best in open plan settings). Ducts can be run in the crawlspace or attic. Just use R8 or better flexduct or sheet metal insulation. Neither is perfect but I wouldn't obsess over having the ducts in "conditioned space" - the air velocity in the ducts prevent it picking up/losing too much heat. Millions of houses have their ductwork in the attic or crawlspace and the systems work just fine.

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Old 04-23-2019, 12:05 AM   #10
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Re: Heat Pump Best Option?


Quote:
Millions of houses have their ductwork in the attic or crawlspace and the systems work just fine.
For unconditioned attic, not efficiently - no wonder the us is one of the highest per capita energy consumers.

R8 is nothing considering the temperature differential - high velocity or not the ducts get warm in heating mode, cold in cooling mode and capacity is lost to the attic. Plus there's duct leakage along with leakage into the attic around the register penetrations which are impossible to seal well long term due to the expansion and contraction.

Crawlspace ducts aren't too bad if the crawlspace is un-vented and encapsulated. (actually attics can be okay too if the roof deck is insulated)
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