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Comment by belval | Hacker News Reader

The article lumps a lot of things together and lacks nuance (I have two heatpumps).

Wall mounted heat pumps are definitely not great to heat your house because of their placement higher on the wall means that your head is getting blasted with hot air while the air at floor level remains cooler. As a retrofit for a house with electrical heating it's just not as comfortable.

As central heating in a newer construction or as a replacement for an older gas furnace it is definitely awesome as it reuses the existing ducting.

Finally the "heatpump doesn't work in the cold" is definitly mostly a myth. There are several models that are spec'ed to go all the way down to -25C.

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I bought property thinking I could retrofit a heat pump air handler onto the existing ducting. Turns out it's all undersized for heat pumps - the air handlers don't heat air as hot as a furnace does, so you need more volume to make up the difference.

Thanks for your insight on the wall units- my installer recommended wall units for the bedrooms for some reason (individual control) but I think I'd rather keep everything ducted, and I neglected to remember the difference having a ducted return would make in comfort.

What’s your plan? I’m likely to be facing the same situation soon, so any insight would be valuable.

Reno'ing a 2 unit house in NE USA, 3300 sqft~

Gut rehab, all new MEP and interiors except floors.

Going all-electric. HVAC to be 3x condensers (1 per floor). One air handler in basement, two in attic space, with the entire system being ducted, or if somehow my installer convinces me, all ducted with exception of wall units in 3 of the bedrooms.

Going for state and federal tax credits, my state has list of approved equipment. I'm going with Mitsubishi hyper-heat for the low temp performance. Even though it should be fine even w 0F winters they quoted resistive backup heaters for the air handlers. State is going to get more strict about what equipment meets their criteria in 2024, I'm getting in under the gun.

Why all electric? Your plan seems big enough that you'll have multiple outdoor units.

Why not have a gas furnace instead of two heat pumps? If the power goes out for an extended period of time (not improbable in the NE) a furnace will happily run off of a cheap generator.

Im not hating on HP, I installed one in my old house (now rental) and will probably add one to my current house. But Im to freaked out of burst pipes to drop a furnace.

Subsidies. So many subsidies. IRA, state. And I get A/C for free, and get to ditch the insane duct system that was built into the house and reclaim almost the entire basement.

I'm in metro Boston which is reliable as far as power goes. Last big outages were 2003 and 1965? My friends who live here longer say the longest they've personally experienced was ~12 hours.

I am considering adding batteries to the house eventually, although I would need to figure out smart load management. Also consider that you can easily make your own electricity (I've got a good south facing roof) but not your own NatGas.

Good answer, but don't forget the 90s Quebec ice storms weren't far from where you are. A week or two w/out power would suck.

In Maine, ice storm of '98. Can confirm, did suck.

Also got to ice skate down the road, across the lawn, and, well, anywhere.

Interesting I had not heard that existing ducting could be incompatible with heat pumps.

For the wall units, one of mine has a better placement that the other so it's not all bad, but the one that is between my living room and dining room is a bit annoying (definitely 1st world problem I know) because my head is really at the right height to get too hot while the rest of my body is still cold.

In other words, wall units can still be an option but double beck the placement so that you don't end up constantly crossing the "stream" of hot air.

In my house they did some math on my ducts, asked me about cold spots in the house, increased the size of the ducting/vent to the bedroom and added one in the kitchen. Didn't add much to the installation cost but I imagine that depends on how the house is constructed.

heat pumps can easily handle your ducts. However, heat pumps designed to work with minisplits, which are non-ducted and do not use a return ... not so much.

It is non-trivial to get the sort of heat pump you would need to retain your ducted system and have it work well, because very few people are going down this path.

You can get units that look like registers, especially if you have attic access. Mitsubishi has them.

The only problem with them is that the installer has to do a good job with the condensate line (for when you run the AC)

I have thought of those as well. They'd have to be on the approved equipment list for my state to get those sweet rebates. They've got pretty routine service required as well yes? Not gonna lie, being able to touch just a couple of air handlers instead of deal with cleaning and changing filters for every room is a plus. Whether it works out I think depends on how well the rooms get balanced, and whether everyone can agree on what temperature their bedroom should be.

> Wall mounted heat pumps are definitely not great to heat your house because of their placement higher on the wall means that your head is getting blasted with hot air while the air at floor level remains cooler. As a retrofit for a house with electrical heating it's just not as comfortable.

I don't get this at all. Hot air rises and cold air falls so you have that problem with all heating and cooling. Maybe if you're talking about a very confined space, but I run my aircon continuously to get the temperature I want and it's generally not blowing on anyone. If it is I turn the fan down, which works just as well but is slower when starting off with a hot or cold room.

> you have that problem with all heating and cooling

This is probably regional, but in Canada it is common to have heatpumps/AC for cold and electrical heating/furnace for heat.

That means your cold is coming from the top of the wall (where the wall unit is) and your heat is coming from near the floor with baseboard heaters. That gives you a better mix of air and a better overall comfort. Furnace exits also tend to be embedded in the floor at the bottom of a wall/window.

Wall mounted heatpumps mess with that paradigm because the air, whether hot or cold comes in near the ceiling. That actually works great for cold, but whn heating the hot air simply won't come down. If you have a second floor it will instead heat up that second floor.

It's not the worst thing in the world, but you definitely have a large temperature gradient from the first floor floor to the second floor ceiling that is noticeable. Especially when going down the stairs. In my case it will be around 19-20C at the lowest point and 23C at the highest.

You generally want air mixing, so it doesn't necessary matter where the units are.

There's an entire procedure that HVAC+D contractors (should) follow when designing a new system (and possibly for retrofits/renos) on just selecting the vents at the end of your ducts for this:

* https://www.acca.org/standards/technical-manuals/manual-t

* https://www.nrel.gov/docs/fy12osti/53352.pdf

What is the D for?

The "+D" in HVAC+D is "dehumidification".

There are ducted units available:

* https://www.mitsubishicomfort.com/residential/products/intel...

I am finding this. The room heat has a distinct vertical gradient. So what is the retrofit that ameliorates this ?

Drawing cold air upward from the floor thru a duct and to the intake near the ceiling won't work passively. Putting a small fan in the duct also seems bogus.

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