My house currently has oil heat, sketchy (asbestos!) ducts, and is poorly insulated. I'm planning to work on air sealing and insulation as time permits, but for a variety of reasons (not the least of which is cost), I want to get some heat pumps installed ASAP before winter comes. Ideally, I want to be able to go this winter with minimal usage of the oil furnance, and perhaps (after air sealing/insulation has been done) remove the oil tank and furnance, and seal up the ducts in the walls. It rarely drops below freezing here in the Pacific NW (and a website calculated only 3729 heating degree days for a nearby weather station), so heat pumps are ideal. I'd also like to get off of fossil fuels, so natural gas isn't particularly desirable. I'm not concerned about cooling, just heating.
The house has 3 levels. The basement will need only heat, but will also be the first spot that's insulated (floor and walls). The main floor will probably also only need heat. The (finished) attic will need both heating and cooling, and my friend who stays there currently uses a window a/c unit in the summer and a plug-in electric heater in the winter. Needless to say, the attic definitely needs massive insulation work. I'm going to do it right at some point; tearing off the siding and putting some rigid foam to address thermal bridging, for example, rather than just blowing cellulose into the walls and crossing my fingers.
I don't want a centralized system; I hate ducts for numerous reasons, and I also don't want a single point of failure (we're going to pretend that losing electricity isn't an issue for now). I figure my best option is 3 heat pumps, 1 ton (12,000 BTUs) each. That will likely be underpowered in the leakiest parts of the house, but will become more than enough as I insulate. An city-supplied energy contractor gave me a $5k quote for a 1 ton mini-split install that he claimed would be fine for the entire house once he did the air sealing and insulation! I don't actually believe him, but I figure it's something that can be adjusted over time.
The obvious choice is between mini splits and PTACs/PTHPs (those things in hotels).
Pros of mini splits: Efficient. Quieter on the inside. Better insulation (a 3in hole in the wall versus a 3ft hole). A $1.2k utility rebate if I have it professionally installed. Easy to compare; they all provide HSPF numbers.
Cons of mini splits: Much more expensive. Requires a professional installer and permit for the refrigerant vacuum stuff. Possibly louder on the outside? The completely DIY option (w/ pre-charged linesets) is less efficient. I'll need to find space outside of the house for the compressor units. Some people don't like the look of the indoor units on the wall.
Pros of PTHPs: Cheap! Uses wall space instead of outside space for the compressor. Doesn't require a permit or lineset charging; very DIY-friendly Provides the option for ventilation, which will be desirable once I do air sealing. Easier to swap out/upgrade/downgrade/replace in the future, if I find the unit is overpowered or underpowered.
Cons of PTHPs: Less efficient. A big hole in the wall will limit future insulation achievements. Noisier on the inside. No utility rebate. Some people may not like the look of it. There's no energy star minimum efficiency for PTHPs, and rather than standardizing on HSPF, they switch between COP and EER.
I was planning to do a mix. In the attic upstairs, where there's wood paneling and it already could be a hotel/BnB, I was going to go with a PTHP. I was not looking forward to finding a place for a mini split compressor - hanging on a ladder on the side of the house, either attaching a compressor unit to the side of the house or running the lineset down 20+ft to the ground. Because of the sloped walls and weird layout, I'm not sure where I'd mount a mini split wall unit. There's an obvious PTHP spot right under a window.
On the main floor, I could do either. Again, due to the layout, I can easily see where a PTHP might go, but there aren't a lot of options for a mini split wall unit.
In the basement, due to the concrete foundation walls, a mini split would make more sense. That would earn me the $1.2k rebate. I could do the majority of the install myself, and just pay for an HVAC tech to come out and charge up the lineset (*if* I can find one).
Unfortunately, I'm unsure how to compare mini split efficiency (typically around 10 HSPF or better for the ones I'm looking at) to PTHP efficiency (3+ COP). I'm also completely unsure how to run numbers to figure out how long the payback period would be for more efficient units. Anything I get is going to be cheaper to run than the $1500/yr I currently pay for oil (and that's not counting the electricity used by the starter/blower/circulator, or my friend in the attic who is not well-served enough by a single thermostat and low insulation, so is currently resorting to electric heat.
My hunch is that a fancy efficient unit (eg a Mitsubishi 26 SEER/12.5 HSPF @ $1800 not including lineset) isn't going to pay off compared to getting a less efficient unit from a less fancy brand (GREE 9 HSPF @ $1060 including lineset). Unfortunately, too many variables make it difficult for me to do a mustachian back-of-the-envelope calculation. I suspect the argument for a more efficient PTHP unit is easier, as the difference seems to be $800 vs $1000 for a more efficient unit.
Given that my current system is already pretty noisy with the vents, I wasn't too concerned about PTHP noise; but I was still planning to start with the attic unit. Install it and see how I like it, and base my decision on the main floor on that. My friend has an ancient noisy a/c running quite a bit lately with this heat wave, so I doubt he'll mind a new, quieter PTHP.
Opinions? Thoughts? Has anyone tried PTAC/PTHP units in their house? Will potential home buyers run away screaming when I go to sell? How can I do some calculations to figure out whether getting a more efficient unit will pay back? Is there anything I'm forgetting to take into account?
