Geothermal?

[SSedan]

Anyone with heat pumps feel like they should have dual fuel? An HVAC guy was telling me you need gas when it is to cold. I live in the Bay Area and it gets around 30 deg + or -

When we had a heat pump in Virginia we often used the "Emergency Heating" switch because the house was not heating. It was just blowing out air at 74 when I set the temp to 78.0. After that experience, we have never again wanted a heat pump for heating.

Again near Green Bay WI, look up the weather averages. My 2400sq leaky late 70s bi-level home does remarkably well on the Fujitsu mini-splits.
The two bathrooms are on baseboard electric still and in sustained -15f or lower i turn on baseboard electric in the late 90s addition living room which is largely glass including a couple skylights.

For a house to need dual fuel in your Bay Area with a modern install you would need to buy the crappiest system made and undersize it and maybe leave a couple windows open.

I say this as a practical person, I am not a green nut, my Tesla is 55% coal powered. Point being I am not being overzealous about environmental impact. Heat pumps just really do work well and minisplits installed well without major surgery to the house. Now if I had room for ductwork I might have not tried it, buti did and am happy.

 

[jboy210]

How old was the heat pump?

This was from the 1980s.

 

[nwdiver]

This was from the 1980s.

Ah; As I said.

I think some tribal knowledge got stuck in their heads ~30 years ago and it's become gospel.

Technology changes. Our perception of it needs to change too. We're not using the same heat pumps they where in the 1980s.

 

[lavalamp425]

Yea I think I do need the two AC units with the house being almost 4200 sq feet. Thanks everyone for the input.

The size of your house is only one factor in how much cooling you need. It is all about heat gain and design temp. My 3200 sf house (in Seattle) needs ~3.5 tons, but I have a 4-ton two stage heat pump that can maintain 74 inside when it is 100 outside. That is a bit oversized, but they don't make two-stage equipment in half-ton increments. Unless you have no insulation and/or tons of south or west-facing windows, 9 tons is crazy even with that size home. For any kind of "normal" house I'd have a hard time believing you need more than 6 tons. Think of it this way: when it is 105 outside, do your systems cycle on and off? If so they're oversized; they should run continuously at the design temp. Get a load calc done, but not by an HVAC company; they're just trying to sell you equipment. It is a cheap way to save a bunch of money on equipment that you don't need.

Anyone with heat pumps feel like they should have dual fuel? An HVAC guy was telling me you need gas when it is to cold. I live in the Bay Area and it gets around 30 deg + or -

The guy is right, but not how he thinks. Modern air source heat pumps work well down into the low 20s, and the variable-drive mini splits work even better than that. So if you're in the upper Midwest (or some other location with super cold winters) then sure, you need a gas backup. Dual fuel is also useful if you lose power a lot and don't/can't back up your heat pump (via Powerwalls or generator). But in the Bay Area, there's no need to bother with dual fuel because you'd never use the furnace.

When we had a heat pump in Virginia we often used the "Emergency Heating" switch because the house was not heating. It was just blowing out air at 74 when I set the temp to 78.0. After that experience, we have never again wanted a heat pump for heating.

Older heat pumps were like that. Newer ones have better heat gain and can push out warmer air. I actually prefer the way our heat pump heats the house; the furnace is too hot.

 

[jboy210]

Ah; As I said.

Technology changes. Our perception of it needs to change too. We're not using the same heat pumps they where in the 1980s.

Thanks. We talked to someone about heat pumps when we had repairs done on the compressor for the A/C unit about 5 years ago. At that time he said it would not be cost-effective to replace the central A/C and gas heating with a Heat Pump. He also mentioned installing the multiple small units with the room/wall units, but that was not something we wanted because of looks and the numbers needed for a 3000+ sq foot 2 story home.

We ended up with multi-zone system. It has greatly reduced our cooling costs and made the house much more comfortable since we only heat or cool a floor when it is needed.

 

[SSedan]

On the aesthetics of minisplits the indoor units oddly blend in. Outside the pipes are covered in rain gutter downspout material and that is more of an eyesore, we don't have neighbors on the two sides of the house affected.
We have two outdoor units each with 3 indoor units 5 are i believe 12k btu and one 18k.

 

[zƬesla]

We also have 2 outside units with 5 (3+2) heads indoors ranging from 6k-18k/each. Installed 5+ years ago for A/C. Last winter we started using them for heat as well and saw electric bill skyrocket, so now we have PV+PW. They're rated to -5, so we also have an oil boiler for forced hot water heating and potable hot water with an indirect hot water tank. Our boiler is 30+ years old and now looking to replace it. Trying to figure out whether to stick with oil boiler or go another route. Gas is not an option and I'm not sure we can get a heat pump that would do the trick for our cold winters.

 

[nwdiver]

Last winter we started using them for heat as well and saw electric bill skyrocket,

How cold did it get? Are you sure that the resistance elements weren't kicking in? Unless you're watching it can be hard to notice.

 

[SSedan]

We also have 2 outside units with 5 (3+2) heads indoors ranging from 6k-18k/each. Installed 5+ years ago for A/C. Last winter we started using them for heat as well and saw electric bill skyrocket, so now we have PV+PW. They're rated to -5, so we also have an oil boiler for forced hot water heating and potable hot water with an indirect hot water tank. Our boiler is 30+ years old and now looking to replace it. Trying to figure out whether to stick with oil boiler or go another route. Gas is not an option and I'm not sure we can get a heat pump that would do the trick for our cold winters.

I believe I could save a few dollars in Green Bay winters with gas heat, but 5" above the basement drop ceiling isn't enough for ducts. It is still cheaper and more even than the baseboard electric.
The Fujitsu system doesn't have backup resistance and once it is truly cold it runs hard so i cna see.it being more than fossil fuels.

 

[zƬesla]

How cold did it get? Are you sure that the resistance elements weren't kicking in? Unless you're watching it can be hard to notice.

Not sure what the resistance elements are. System worked fine down to the single digits. Once we got to below 0F, it struggled to keep temp and we relied on oil heat (typically set several few degrees below mini-split temps as a fallback).

 

[jboy210]

Not sure what the resistance elements are. System worked fine down to the single digits. Once we got to below 0F, it struggled to keep temp and we relied on oil heat (typically set several few degrees below mini-split temps as a fallback).

On our old Heat pump, there was an electrically powered heater in addition to the thermal pump. This electric heater generated heat by heating a series resistive heat elements, sort of like a toaster. It kicked when it was too cold for the pump to extract heat from the air, or you manually turned a switch because the system was blowing cold air.

 

[strider]

Our house was built in 2001 and those units (Armstrong I think) would barely work at 30F. The air coming out of the ducts would barely reach 80F. The units ran constantly and would severely dry the air in the house. We had to run humidifiers in every room.

On my central heat pumps, the resistive elements were on a separate breaker. I actually flipped those breakers to make sure they never kicked on. But in the winter we had to use the wood stove a lot.

As others have said, newer units can pump heat at much lower temps. But for me, it's about the temp differential. The ground is always 55F so you get a lot more heat transfer than going to outside. The geo unit can output much higher temperature air and with variable speed pump and fan, it doesn't blast us with barely warm air. Very warm air just wafts out of the registers. We haven't used the humidifiers since.

All that to say, in the Bay Area, current generation air source heat pumps will work perfectly fine. Geo would be overkill though I appreciate no having the ugly and noisy units sitting outside buzzing away all the time.

 

[nwdiver]

I appreciate no having the ugly and noisy units sitting outside buzzing away all the time.

That's also changed. I guess 'beauty' is subjective but you can barely hear most modern outdoor units. Most of the time I can't hear mine unless I'm < 5' from it...

 

[zƬesla]

Ours are Mitsubishi Mr Slim. I like how quiet they are. I’ll need to read further on the “emergency” setting, however if anything that will just make the electric bill go even higher as I don’t see our solar handling their winter load very well. I also like the idea of having an alternate fuel in case of an extended outage which would conserve battery life as we’d turn off the minis. It’s looking like another oil boiler with a variable speed circulator will probably be the most cost effective for us. May put decision off until next year so we have at least one winter with solar.

 

[shs1]

Anyone with heat pumps feel like they should have dual fuel? An HVAC guy was telling me you need gas when it is to cold. I live in the Bay Area and it gets around 30 deg + or -

You have to be careful here with the definition of heat pump. It is true that an air source heat pump becomes inefficient when the temperature approaches the freezing point as it seems the air does not have the heat capacity too supply the heat to "pump" into the house.

A ground source geothermal heat pump uses the earth about 6' down as a heat source where it is at a fairly constant temperature (~50° F IIRC) regardless of season. Heat capacity is not a problem. Geothermal heat pumps work just fine in the cold. We see 10° F at night in the winter and our heat pump handles it, no problem.

 

[jakespeed]

From the Tesla app, it seems that unit uses either 5 or 9 kW when running. When it kicks in, it runs for not too many minutes before turning off. Also FYI, my home is about 4000 sq ft, but made with SIP panels and so very well insulated. My 5-ton unit heats and cools our house, no problem.

if it "runs for not too many minutes before turning off" it could be oversized. google "short cycling a/c" short cycling will wear out the unit more rapidly than normal

 

[shs1]

Thanks, but It typically only runs a few well separated times a day in the summer. My winter heating demand is higher.

 

[Cstreet]

Anyone with heat pumps feel like they should have dual fuel? An HVAC guy was telling me you need gas when it is to cold. I live in the Bay Area and it gets around 30 deg + or -

I'm in the SF Bay and we had a Mitsubishi heat pump installed last year to replace a gas heater and old AC unit. It works great and no more gas! If you get a great heat pump like the Mitsubishi or LG systems you don't need dual fuel.

And it works nicely with our Powerwalls and solar. It uses 2.5-3.5kw to heat in the winter and then 2.5-4kw to cool. We have a 3000 sq foot house with heavy sun exposure so it's heavier on the AC load.

 

[twocoasts]

Last year I had two geothermal/ground-source heat pumps installed by Dandelion. I'm in a heating-dominant climate (mid-Hudson Valley, low altitude), and the only realistic option to adequately back up air-source heat pumps would have been heating oil or wildly overpriced propane. My system, sized primarily for heating load, is a total of 9 tons (one 5 ton unit and one 4 ton) because the house is about 4500sf and has a lot of glass, so despite having good spray foam insulation and high-quality triple-pane windows there's some heat loss. One year in, I'm happy with the results so far.

My three Powerwalls provide enough juice to run just one of the two heat pumps but not its backup heat electrical resistance coils, plus other intermittent loads (an induction cooktop, well pump, water heater, fridge, freezer, and some LED lighting and electrical outlets). To make this work required installing a soft-start on the heat pump. There's also a generator for the worst-case scenario of an extended cold-weather electrical outage with insufficient solar+battery to cover heating needs.

The heat loss calculations for my home showed that with just one heat pump & no backup coils I could still keep the house from freezing in even an extended outage in the most extreme winter weather. And I have a high efficiency woodstove for more heat if need be. We haven't yet experienced an extended electrical outage during very cold weather yet, since this past winter the weather was mild (which also means fewer outages here). So I can't report firsthand how well this will work. I'm not even sure if the heat pump has cycled on during an electrical outage a single time.

My system required three vertical wells. Drilling was a mess, the vibration stirred up some clay in my drinking water well for a couple of weeks, and it required some space (although not as much as horizontal loops would have). But now that we're past that phase, I have to say one of the things I like about geothermal is aesthetic: no ugly compressors outside the house, and likewise no minisplit head units inside. That wouldn't have been enough reason to choose it for me, but it's a nice bonus.

 

[nwdiver]

I thought this was funny. They were explaining how the high cost is a 'myth' of geothermal systems. 'If you ignore the cost of the well, they're only ~30 - 50% more expensive'........ sure.... and if you ignore the cost of batteries an off-grid home is cheaper than being grid tied.....