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Advice for a new heat pump installation in a 2 story house

2.1K views 5 replies 4 participants last post by  Bazooka Joe  
#1 ·
We would like to replace our gas furnace of 80,000 BTU capacity with a heat pump for both heating and cooling.

We live in a 2 story townhouse, 1940 sq ft, built in 1977, no basement, attic with old insulation, double pane windows and sharing walls on North and South side. We are in Sunnyvale, California.
Ducting is in attic for upstairs. Down stairs is in a ceiling soffit so it cannot be replaced.

I did a load calculation myself using free online tools:

coolcalc says:
Heating: 29,400 BTU/hr
Cooling: 19,700 BTU/hr

betterbuiltnw says:
Heating: 28,200 BTU/hr
Cooling: 34,400 BTU/hr

Based on my smart thermostat historical data and my current gas furnace using instructions at (search for "How to Find the Right Size Heat Pump For Your Home" at Google) for the coldest hours of the past winter I got:
Heating: 26,667 BTU/hr

All three methods gave a similar load calculation for heating so I feel confident about that value. Not sure about the big difference between the 2 online tools in cooling though. In any case, a 3 ton heat pump seems like a good size for our house.
The rule of thumb based on square footage recommends a 4 ton heat pump. The couple of HVAC installers I talked to also gave quotes for 4 ton heat pumps but without doing a manual J calculation.
Looking at the public dataset at techcleanca most in my area for similar square footage houses went with a 4 ton heat pump. But maybe those were single family houses. My assumption is that since 1/3 of our house (1st floor) doesn't have unconditioned ceiling, and we share walls on both North and South sides we should need a smaller system size than others. Is that accurate?

1. How much should I trust the above methods calculating the size versus what the HVAC installers are recommending? I don't quite trust them since their incentive is to sell more.


Currently we are experiencing a temperature difference between the 2 floors, up to 10 degrees, but I think, at least in the winter, this is because the current gas furnace is oversized and only works for a couple of minutes at a time without a constant fan circulating the air in the house. Even during the coldest hour in the past winter I see on the historical stats of the thermostat that the gas furnace worked 20 minutes with multiple breaks within that hour. Is my thinking right?

Options we got from HVAC installers:

A. regular heat pump (Carrier) and single air handler with existing ducting
B. variable speed heat pump (Mitsubishi) and single air handler with existing ducting.
C. variable speed heat pump (Mitsubishi) and two air handlers. Ducting for upstairs will be replaced.
D. variable speed heat pump (Mitsubishi), one air handler for upstairs with existing upstairs ducting, one mini split unit for downstairs.
E. regular heat pump (Carrier), 2 zone damper system. Ducting for upstairs will be replaced.


2. Could you rank the above options in terms of comfort? Assuming we want the same temperature through out the house, what temperature imbalance between the 2 floors should we expect with each option?

3. Would option B achieve comfortable results if it works constantly at its lowest speed for most of the day circulating air? Will we get an uncomfortable draftiness feeling in the winter if the fan circulates air?

4. If we go with option A or B, could we manually close the existing damper that goes downstairs (or the downstairs registers) in the summer if we only want cooling upstairs? Is the static pressure going to be a problem even for a variable speed system in option B?

5. If we go with option B, could we keep the system and go with option D or E in the future?
 
#2 · (Edited)
Why not pay a small fee to have it done to compare to your free ones, there are load calculation online that are more detailed. Thinking you want to get that part correct beforehand. You can also have them check your ductwork to see if it will be correctly sized, or if it needs some modifications.

If your getting bids ask for AHRI matched systems, as money in your pocket rebates from your state comes into play.

There is also the Federal Tax Credits.

https://hvac-talk.com/vbb/attachment.php?attachmentid=845535&d=1678474996

https://www.energystar.gov/about/federal_tax_credits

Regular Heat Pump, less complicated more generic parts typically lower efficiency, louder vs variable Heat Pump, more complicated system, more functional parts, probably more proprietary parts $$ once manufacturers warranty expires. Quieter, they say more about comfort options.

Should come with a one year minimum labor warranty, but certainly could be longer.

Believe if you go with a Diamond Dealer for the Mitsubishi you get an extra two years compressor and parts warranty to 12 years whereas the Carrier probably tops off at 10 years parts and compressor.

You can purchase a extended labor warranty from the manufacturer also if that interest you, typically they go up to ten years. I believe Mitsubishi recently got on board with offering them, whereas Carrier had them for many years.

Getting bids for other brands or your narrowed it down to those brand models?

You will know how well your system of choice was installed and set up and operates within a short period of time, especially the more complicated variable by the amount of times you have to call the Installing Contractor back to tweak, adjust, do modifications etc. under the labor warranty period. You will also know pretty quickly how experienced the Tech. they send out is familiar with you model brand on how long it takes the Tech. to correctly diagnose the issue and make repairs/corrections.
 
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#5 ·
Why not pay a small fee to have it done to compare to your free ones, there are load calculation online that are more detailed. Thinking you want to get that part correct beforehand. You can also have them check your ductwork to see if it will be correctly sized, or if it needs some modifications.
How much would that cost? What kind of tests can they do for the ductwork?


If your getting bids ask for AHRI matched systems, as money in your pocket rebates from your state comes into play.

There is also the Federal Tax Credits.
Yes I'm aware of the $2,000 federal credit. There are currently no state rebates in CA but there are 2 local rebates: $2,500 and $1,000 that I'll be eligible for both as long as the system is ≥ 17 SEER.


Regular Heat Pump, less complicated more generic parts typically lower efficiency, louder vs variable Heat Pump, more complicated system, more functional parts, probably more proprietary parts $$ once manufacturers warranty expires. Quieter, they say more about comfort options.
I'm leaning towards a heat pump with variable inverter for being quieter and hopefully better comfort having air circulation through out the day. The additional upfront cost isn't that much. But the additional maintenance costs wasn't something I considered.


Should come with a one year minimum labor warranty, but certainly could be longer.

Believe if you go with a Diamond Dealer for the Mitsubishi you get an extra two years compressor and parts warranty to 12 years whereas the Carrier probably tops off at 10 years parts and compressor.

You can purchase a extended labor warranty from the manufacturer also if that interest you, typically they go up to ten years. I believe Mitsubishi recently got on board with offering them, whereas Carrier had them for many years.

Getting bids for other brands or your narrowed it down to those brand models?
I wasn't aware of the added warranty years if I go with a diamond dealer. Thanks. I'll reach out to a couple of them.
Actually one quote I got is for Gree. I'm planning to get a lot more quotes but I first want to figure out the size and whether I should go with continuous air circulation to avoid heat imbalance between the 2 floors, or if I should go with 2 systems or 2 zones.


2 Stories
2 Systems
! ! !
Yes I'm afraid I'll have to go this route but options C, D, and E are quite more expensive.
I was wondering if option B could achieve comfortable enough results having continuous air circulation and only go with one of the other options later.


22,900 BTU/HR HEATING @ 36'F __ ~ 370 Therms.

20,100 BTU/HR _ Cooling _


How many THERMS Natural Gas are used for Heating ?

2.5 TON OR.
3 Ton , 2-stage Heat Pump
Throughout 2022 ~330 Therms was used for space heating, ~140 for water heating.
On the coldest days it was ~4 Therms.


@All, I'd appreciate if you could answer questions 2 to 5 in my original post. Thanks!
 
#4 ·
We would like to replace our gas furnace of 80,000 BTU capacity with a heat pump for both heating and cooling.

We live in a 2 story townhouse, 1940 sq ft, built in 1977, no basement,

attic with old insulation, .

double pane windows and .

sharing walls on North and South side.

We are in Sunnyvale, California.

Ducting is in attic for upstairs.

Down stairs is in a ceiling soffit so it cannot be replaced.

I did a load calculation myself using free online tools:

coolcalc says:
Heating: 29,400 BTU/hr
Cooling: 19,700 BTU/hr


Based on my smart thermostat historical data and my current gas furnace using instructions at (search for "How to Find the Right Size Heat Pump For Your Home" at Google) for the coldest hours of the past winter I got:
Heating: 26,667 BTU/hr

All three methods gave a similar load calculation for heating so I feel confident about that value. Not sure about the big difference between the 2 online tools in cooling though. In any case, a 3 ton heat pump seems like a good size for our house.
22,900 BTU/HR HEATING @ 36'F __ ~ 370 Therms.

20,100 BTU/HR _ Cooling _


How many THERMS Natural Gas are used for Heating ?

2.5 TON OR.
3 Ton , 2-stage Heat Pump
 
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#6 · (Edited)
How much would that cost? What kind of tests can they do for the ductwork?

https://loadcalculations.com/

https://aircondlounge.com/hvac-ductwork-design-guide-layout-duct-size-cfm/

https://www.acdirect.com/air-duct-design-sizing

I believe the Mitsubishi and Daikin Fit variable come in .5 ton increments, whereas most come in whole tonnage increments. If your looking for excellent/outstanding manufacturers warranty, the best in the industry IMO The Daikin Fit comes with a 12 year whole new outdoor unit if compressor ever fails in the 1st 12 years and 12 year parts and coil. If you go Daikin Air Handler or coil, that also has a 12 year parts and coil warranty, whereas most every one has the standard 10 years compressor, parts and coil. Or…..

The Amana ( under Daikin umbrella ) https://testwww.amana-hac.com/products/heat-pumps/aszs6-s-series

has a limited lifetime whole new outdoor unit to original registered owner if compressor ever fails and not a replacement compressor.

If extended labor warranty is a option, there are only two manufacturers that backs their own extended labor warranties, York and Daikin, the others, including the big recognized names like Carrier, Trane, Lennox, Rheem, etc. use a 3rd party.

Don’t think Gree offers extended labor warranties, system manufacturered/assembled 100% in China.
 
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