School me on heat pump HVAC systems

[ScaldedDog]

I know some of you guys are really into this stuff. I'm not, but need to come up to speed quickly.

Situation:

40+ year old 2000sf home in FL. Thin walls, thin bat insulation. Existing (12SEER?) gas furnace and AC unit is 12 years old, and needs a $1700 repair that may not fix the problem. (Blower motor won't reliably start in heat mode.) We're thinking of replacing the whole thing. Gas is cheap, as is electricity ($.11kwh).

My priorities are AC performance and noise reduction (as the existing blower motor is very close to the return vent and is really loud). Heat performance and cost to operate are less important, but need to be reasonable.

Vendor is suggesting a Bryant 17SEER-2 4-ton 2-stage heat pump system. Other options are single stage 3.5-ton systems for 2/3 the price. Gubment may give me some of your money to pay for the larger system.

What questions should I be asking?
What should I watch out for?
How can I goof up a decision like this?

Talk to me...

Mark

 

[dan1554]

Similar questions for a different situation (air-water). But I always walk away wondering how there can be 99999 different heat pumps on alibaba and no evidence on the internet of anyone using them.

 

[Lastresort576]

I need to get better versed in this stuff myself. I have a Lennox system.
But I will say that my heat pump struggles to warm my house(built in '23; 3,300sqft) when its below freezing for any extended period of time. I have to set the thermostat to a higher than desired temp in order to manipulate it into running longer. When its around 20* outside it pretty much runs non stop. So with that said, I do wish I had backup propane heat for the cold days..Which is only about 2-3 weeks a year.

As for the AC aspect, its great. the house stays as cool as I want it to, even on the hottest of days here in NC. Not sure if any of this helps you, but I wouldnt hesitate to get a comparable system if I was in FL.

 

[Romer]

Florida with a heat Pump would eliminate the furnace. I have a Dual system where I have the Natural gas furnace come on if the temp is below 45. I can set it lower, it takes more lectricity the colder it gets and gas is cheap.

If you look in the solar section of this forum you can find my thread on the effects of going with Heat pumps vs the older ACs I had

 

[gungriffin]

AC performance and noise aren't effected by it being a heat pump.

The noise is going to be a function of the blower motor. I'm guessing that a new motor will be substantially quieter than what you have installed presently. You'll probably also find it's even quieter still because the blower motor is a two-stage motor. That's just a fancy way of saying that it has a low and a high setting. Usually with heat pumps the outside compressor is either multi-stage or infinitely variable. This allows the unit to run more often at a lower setting which will oftentimes increase the efficiency. Ideally, you want these units to run almost 24/7. Doesn't hurt the units to do so, and it also has the effect of running the air through the filter continuously. This will greatly improve the air quality inside of your home.

I highly recommend you go with an aprilaire 5000 electronic air filter unit. It's a bit expensive at about $700, bit it has enough upsides to make the higher price well worth it. It's a 4-in filter so flows better. It also filters at almost the level of a HEPA filter. It'll even get rid of smoke and odor inside of the house. This is the unit that I have installed in my house. I have nothing but good things to say about it.

When you talk about performance, that's going to be a measure of the tonnage rating and not whether it's a heat pump or not. You might ask the company to justify how they arrived at 4 tons if that is what they are recommending. Very frequently, you'll find that they just throw back in whatever size they pull out. If you find that it's not cooling your house well enough, then the unit you presently have might have been undersized your house. If you're willing to spend a few hours and about 200 bucks, you can get a manual j done. A manual j is how you calculate your heating and cooling needs. It takes into account cubic air volume, the exterior envelope of the house and any any penetrations in the wall including windows and doors. You could always just roll the dice and ask them to install a 5-ton unit if you need more cooling.

One item to be aware of is that a traditional heat pump will only be able to produce heat at full capacity down to approximately 35 to 45° f. At that point you might begin working with diminished capacity. It will still probably provide heat down to maybe 5° f, but it will begin to do it at a lower tonnage rating and efficiency. You can install a heating coil into the indoor Air handlunit if you don't anticipate hitting the lower end the unit can provide very often. The heating coils basically just a fancy hair dryer. The primary issue is that it pulls a ton of power when it's being used. Probably 15 kW in your case. So you definitely don't want to use it if you don't have to. I don't know where in Florida the house is but if you have a lot of colder days and want an all electric unit you can also just have them install a cold climate heat pump. That's what I have installed in my house. It provides heat at full rated capacity down to about 5° f, and is capable of providing heat down to about -22° f. I had no issues heating my house two Winters ago at a -19° overnight low. I didn't even have to use the emergency backup heat.

 

[ScaldedDog]

Great answers, guys!! I'm really trying to not have to buy a system, so let me get down into the weeds a bit. If any of you are, or know, an HVAC tech, I'd be interested in talking to you, or them. Here's the deal:

The $1700 repair I mentioned is for a replacement circuit board, part number HK42FZ0273313. I've found the same base part number that looks to be identical, but has a different last 4 digits -3715. I'm trying to figure out the significance of those digits. Is it just a hardware or firmware rev number, but is functionally identical, or is there a real functionality difference? The board is only $480, so I'm motivated to figure this out.

Carrier/Bryant won't talk to me, and just want to refer me to the local dealer who is apparently trying to pay for their fancy new office building out of my wallet.

Mark

 

[dan1554]

The circuitry looks pretty simple if Im looking at the right thing. Might be able to check it for visible damage or get a friend who is good with electronics (Im sure there are people on the board) to take a look at it. Again if Im looking at the right thing, it seems to be through-pin which would make repairs relatively simple.

 

[DaveInDenver]

Both HK42FZ027-3313 and HK42FZ027-3715 seems to point to the same thing via web search. The board has seems to have a -3121 extension.

At the same time HK42FZ0273313 and HK42FZ0273715 get no returns for me.

Knowing the exact part number, all characters and groupings, is usually an important detail to decoding it. There's no standard for a part numbering unless one is specifically used, such as with military or government procurement. But even a company's internal nomenclature doesn't have to match external and customer nomenclature.

Anyway, does it look like this? This is Carrier HK42FZ027. I've also come across this board as being called part number CEPL130934-01 and CEPL130934-02



White-Rodgers show a universal replacement, so it must be fairly common. This replacement covers several Carrier, Bryant and Payne boards.


I have not been able to find a schematic, which I'd personally want as a starting point. I've troubleshot a couple over the years but I had schematics when I did them. Haven't found a really good high res photo either.

These furnace boards are usually pretty simple and may not even have a microprocessor. Unless the issue is obvious, like crispy parts, it might not be super easy. Like knowing if a value (although through-hole parts just read the resistor color bands) is drifted or slightly wrong would be more significant reverse engineering. But if you buy a good one to use for comparison there's no economic point to fixing the old one unless you want to keep it as a spare.

There's only two chips that might be MPUs and if they happen to be they would almost certainly be very old 8-bit PICs or something like that to imply there's firmware versions. But I see no obvious indication of support circuits (like a header for debug or programming or more important, a crystal for a clock) that would make me think that's there's one. There's a "PLT" header close to a jumper for test, so who knows? My first guess is those are logic chips, simple AND/OR. That replacement White-Rodgers OTOH I would be surprised if it did NOT have a microprocessor on it, however.

The dashed (as it were) part in the case of lacking an MPU might just indicate board revisions or differences in what's populated. That could be nothing, like they had to spin the board due to a part obsolescence, or important in that they changed circuit function. Only they'd really know. My suspicion is minor changes since these seem interchangeable but that's pure speculation.

 

[DaveInDenver]

Not that it's convenient to you or anyone really, but as always mi banco de trabajo de electronica es tu banco de trabajo.

But back to your regularly scheduled program from the "Happy to try a repair" tangent.

 

[ScaldedDog]

Man, you guys are good. I hate to ask electrical questions here, knowing how much time and effort some of you will put into them. Thanks!!! I really appreciate it!

Dave, I was able to confirm the White-Rogers part will work, for a whopping $223. The OEM HK42FZ027 will also work, but for $480 from repair clinic. Since I don't know for certain a circuit board will resolve the issue, I opted for the cheapest alternative.

On a business note, I'm all for making money, and don't begrudge anyone their margin. But $1700 for a part that any Tom, Dick or Harry can buy for under $500, at a margin the seller is happy with? That's not margin, that's "we hate our customers and think they are idiots" pricing. [/rant]

Mark

 

[DaveInDenver]

In 2025 a replacement that's only $223 is a bargain. Whole industries are designed to make DIY difficult. Carrier might not let their dealers sell retail replacement parts, so the risk is being shut out from buying new furnaces or getting put on a naughty list with higher wholesale prices.

So they pass along the pain to you. If you really want to fix it yourself you offset their pain from higher up or find one of the few remaining places that only do appliance repair supply.

Just more of The Enshittification of Everything.