There have been several different threads on this forum over the past several weeks concerning mini split heat pumps. I suggest you check these out and review them and then come back for questions.

TD

I don't have great heating demands so I don't have the Mitsubishi hyper heat system, but it is very neat technology. I think that they have patent protection for their flash injection scheme.

I guess anything would be better than a resistance-heated electric boiler in your climate! Mitsubishi make what looks to be a nice DIY minisplit system.

I looked on the web for recommended installers in my county; there were none, but four in the adjacent county. I went to one of them, and they recommend a Fujitsu model which works down to -15°. Even though they usually only do commercial installations, they are willing to consider my project. There are two other HVAC contractors I can contact and I will check with them (the fourth was clearly a handyman).

works down to -15 degrees...humm...interesting to ask what size system and how many BTUs produced at -15 degrees.....any electric backup strips?...

IMO

I would suggest ‘correcting’ your existing situation by having your electric boiler supplement an air source hydronic heat pump that would use your existing electric hydronic boiler only as a backup. This way, you would have very efficient in-floor hydronic heating and hydronic cooling. All with one well-integrated, efficient system.

The first link contains a video explanation of the system. The second link takes you right into the technical weeds but what is of interest is that same system can be used for every conceivable heating and cooling application – including, zoning, DHW, pool, spa or snow melt!

See page 26 of the 2nd link.

Links 3 & 4 illustrate the type of fan coil units for both heating and cooling that would provide zoned hydronic cooling and heating, that in heating mode would work with your existing boiler as well as the heat pump, to provide a quick boast in indoor temperature when needed as in-floor heating is rather slow to react.

That’s a whole lot to chew on but technically the best single, integrated system for your existing situation other than geothermal.

https://www.nordicghp.com/product/nordic-products/air-source-heat-pump/air-to-water/

https://www.nordicghp.com/wp-content/uploads/2018/03/001970MAN-02-ISSUE-02-ATW-Series-Two-Stage-R410a.pdf

http://www.multiaqua.com/index.php/water-fan-coils/cffwa-universal-2p

http://www.multiaqua.com/index.php/water-fan-coils/cffwa-universal-2p

IMPO

SR

Thank you, fsq--- These Nordic systems seem to be overkill, and there are no US installers in the NE (there are several in the Montreal area, and they might be possible).

I got a telephone estimate from the one installer I mention above, for a Fujitsu system. By referring to some of his recent installations, he thinks my cost might be about $7500 (for a 24000 Btu system). Between his and my busy schedule, I cannot get a visit from him this month but we have a tentative meeting in August.

He is quite familiar with my type of situation, but he thinks that, since I already have an existing heating system with which I am very satisfied, I needn't get a system which needs to work as low as -15°F. My primary interest is in cooling, so the system would be sized for that.

I guess you are deciding whether you want heat pump or cooling only, and if heat pump, what low temperature you want to be able to use them to. My memory tells me that the cost of heat pumps was not much higher than cool-only when mine went in. The lower temperature heat pumps are going to cost more, but you may very well find that they will return more than that cost with a little calculation. The trouble with that calculation using fuel cost only is that it is significantly more expensive to operate a heat pump than resistance heaters. You'll have to be more creative to factor that in.

IMO, mvthike's situation is what mini splits are made for, adding (a little) cooling to a home with established heating without ducts. There are a lot of heat only homes in climes with low cooling needs. ( A lot of them have window units running for a few weeks.) That is, of course, why the installer mentioned is "quite familiar" with that situation in the 'daks and far outside. This particular situation is complicated by the fact that the most economical heating fuel choice, for many, is not available. (Outdoor wood-fired boilers are not unheard of in that area. I bet there are dealers for those a lot closer than for the air-water heat pumps.)

My memory of earlier posts combined with this one says mvthike's "overkill" response is partly due to the fact that this home is unoccupied more than it is occupied so payback with higher cost, highest efficiency, methods is going to be long at best and may reach never.

Tigerdunes, I think that there used to be high wall mini splits with resistance heat. I think I saw info about them when I first started looking at them but they disappeared shortly afterwards. My understanding is that someone decided that heaters of that type with plastic cases were not a good idea. I could be all wrong about this. I do think that is available with their mini ducted equipment.