2nd minisplit?

[Max W]

As we get on in years I want to rely less on wood and am considering adding a second minisplit. I am thinking also about a time if one of us or both are here and unable to handle wood. Maine incentives plus tax credits make this addition look attractive. With a moderate income we can get a rebate of 60% up to six thousand dollars on an installation. A problem is I don’t have an ideal place for a second and I don’t know how the possible locations I have would do.

My 15,000 btu Fujitsu heat pump, 18,000 in heat mode, in the livingroom along with the kitchen cookstove keep us comfortable in winter, living in the 900+ sq ft well insulated downstairs of our house. The windows are fairly new and the front of the house is buffered by an enclosed porch. The cook stove is rated at 34,000 btu’s, I believe, and is sufficient to heat us by itself if I feed it well and more often than a larger stove. We also have a 20 year old boiler that is seldom used. That would be our backup in a deep cold snap. Also, whatever shape we are in the stove isn’t going anywhere and an having some wood easily available would be prudent.

Our layout and circulation are pretty good for the single minisplit and heat gets from the livingroom to the kitchen, although it may be a couple of degrees cooler there when running the minisplit alone. Our bedroom and bath stay comfortable enough with the two heat sources in the coldest weather and with the split alone when we run that way. The 36 inch doorways help some there. My wife did use an electric heater to nudge the bedroom temp twice this year. When we rebuilt we insulated between the 1st and 2nd floors and in winter allow very little heat up the stairway. Ideally I would put a second unit in the kitchen dining area but I have no available wall space inside or out. With the cookstove we burned a little less than a cord this warmer year.

I have space to put a second split in the livingroom on the other end of the same wall as the existing one. It would be a little lower on that wall to fit under an exposed beam. The location for the outdoor unit is convenient there doesn’t get roof run off. Another location could be on an interior wall in that same room. That might require chases for the lines, not so attractive to me. A third is in the bedroom. I think that would need to be a smaller unit and getting heat to the rest of the floor may be difficult.

As I write and draw this out it is occurring to me that I would need another 15,000 btu unit to even come close to replacing our use of the stove. While not ideal I’m thinking the living room wall location that would have it blowing either straight toward the kitchen or with fins angled to join the stream of the existing split along the front of the house. That may be my best option. I picture only one unit running most of the time. In colder weather with both going I wonder if managing short cycling would be a problem. Right now our existing minisplit is 8 years old and some redundency would be nice. Running as the backup may add some years to the life of the Fujitsu .

I’m trying to figure if this a workable solution and looking gain some more insight before getting estimates to see if it makes economic sense. The sketch shows our layout and locations where I see a new unit could go.

 

[stoveliker]

There are units that can be installed in a ceiling, especially if there is an attic above.
I know Mitsubishi has them.

Would that be an option?

 

[bogieb]

If you place the second unit in the same room as the first unit, I think that they will both run basically at the same time since they are sampling the same air, so short cycle all the time.

I have a 960 sq/ft main floor that I have a 24k outdoor with a 15k head unit in my living room and a 12k head in my office. I oversized the office to keep it cool in summer because of the heat from all the electronics - and it goes into my kitchen too. Since I WFH, I use the office unit on a regular basis to stay comfortable during the workweek without turning up the heat/turning down the AC in the living room. I shut it off when I am done for the day and don't run it during the weekend at all. I also have a Fujitsu system.

Since the bedroom is where you used an additional heat source, that is where I think it would be best to place a second unit. You could probably get away with a 6k unit in the bedroom - or they also have a 9k unit. However, if you are looking to use it if the other mini-split goes down, that would not work well.

Have you thought about going ahead and replacing your existing outdoor unit with a new 24k 2-line unit? That would ease fears of it developing issues as it ages. The downside to a 2-line outdoor unit is it is technically less efficient that running two entirely separate units. At the same time, you would only need to service one system instead of two to keep it running optimally.

 

[EbS-P]

There are units that can be installed in a ceiling, especially if there is an attic above.
I know Mitsubishi has them.

Would that be an option?

You can get low wall units too. The ceiling cassettes need a condensation pump. Pumps should be avoided if possible if you use the AC.

You could install two heads with one compressor. One in bedroom one in living room. I’m not a huge fan multi head installation but they are a thing.

I will throw out as an option just replacing the current unit with on with higher output unit. Seems a bit wasteful.

 

[Max W]

There are units that can be installed in a ceiling, especially if there is an attic above.
I know Mitsubishi has them.

Would that be an option?

Thanks for the suggestion. I had thought about floor models but not ceiling . Our house does has a second floor but bigger the problem is that exterior walls surrounding the kitchen dining area have don’t have a place for the compressor unit of a minisplit. Same with interior space for a wall or floor unit.

 

[EbS-P]

Thanks for the suggestion. I had thought about floor models but not ceiling . Our house does has a second floor but bigger the problem is that exterior walls surrounding the kitchen dining area have don’t have a place for the compressor unit of a minisplit. Same with interior space for a wall or floor unit.

In the deck elevated?

 

[Max W]

bogieb and EbS-p, It makes sense short cycling would be a problem two units in one room when both are needed. Will give up onon that option. The bedroom is still a possibility. 9k would be that much more than the envelope now has. Guessing 12k would short cycle?

I have read how going with multi interior units is less efficient, and possibly more trouble? I’m fine adding a new second single minisplit. It’s more a finding the location. I have thought about replacing the existing unit with a larger one. The heat does get distributed fairly well with the existing split. It’s more a matter of btu’s. It does seems a shame to take out something that has given no trouble. No idea how long these are supposed to last. Also I don’t know if that replacement would qualify for Efficiency Maine’s rebates. If I was going to look at a single larger unit I would wait. The units with the newer refrigerant are expected out next year and may have better capacity at lower temps. Don’t know if the costs will also go up.

 

[stoveliker]

For heating floor models are good.

I have one unit with a condensation pump as it's in my basement just below the top of the blocks. Not a problem.
If course a problem arises when they fail. In my case it's vinyl on concrete slab, and I made an access door. If it's on a wood floor with livable space underneath, a failing pump would give more issues.

 

[Max W]

In the deck elevated?

Missed this. The deck is on posts, maybe 3 ft off the ground.

 

[EbS-P]

bogieb and EbS-p, It makes sense short cycling would be a problem two units in one room when both are needed. Will give up onon that option. The bedroom is still a possibility. 9k would be that much more than the envelope now has. Guessing 12k would short cycle?

I have read how going with multi interior units is less efficient, and possibly more trouble? I’m fine adding a new second single minisplit. It’s more a finding the location. I have thought about replacing the existing unit with a larger one. The heat does get distributed fairly well with the existing split. It’s more a matter of btu’s. It does seems a shame to take out something that has given no trouble. No idea how long these are supposed to last. Also I don’t know if that replacement would qualify for Efficiency Maine’s rebates. If I was going to look at a single larger unit I would wait. The units with the newer refrigerant are expected out next year and may have better capacity at lower temps. Don’t know if the costs will also go up.

I’m guessing any amount of money saved or lost due to efficiencies of new and or multiple head systems would not have impacts on your decision. We’re really taking less than 10% at low output and similar at higher output. What you may gain is increased output at low temps but nothing I have seen is really over 2.1 COP below single digits. While you still want too burring some wood during this coldest 10-20 days would have more cost savings than any other system.

It seems that with two smaller units short cycling could be solved just by temp settings and a remote thermostat location.

I’d probably just get a new 24k btu unit and run the old one for AC and supplement when it’s really cold…..

Missed this. The deck is on posts, maybe 3 ft off the ground.

I have a spot under my deck it’s 3-4’ of vertical clearance that I may install my compressor.

 

[bogieb]

Replacing current outdoor unit: some places give you trade in, much like a car, and they will install used units for customers who can't afford new (or sell to DIY's). Also, could sell on CL or FBM, although I wouldn't want to go thru the trouble since I couldn't really answer questions about the system besides it worked fine when removed. I totally understand reluctance to replace something that is working perfectly well and I would struggle with that too.

Separate system: You do not have to place the outdoor unit directly under the indoor head. You could still place the compressor along the same wall as your current one. If you have a crawl space or basement, the lines could go thru there. The lines for my office go outside then straight down to enter the basement, along the basement ceiling, and exit right behind the outdoor unit). Or, they can go along the exterior of the house - although that is less efficient and you may have issues with the aesthetics. Or, perhaps it can fit under that deck (good thinking @EbS-P )

 

[Max W]

Had our minisplit cleaned and what a difference. I had spray cleaned the condenser with a hose and routinely cleaned the the air handler filters but never had that indoor unit cleaned. While inside didn’t look bad after 8 seasons the fins, tubes and fan were dirty enough to apparently seriously limit air flow and heat exchange. The guy came with his spay cleaner, pressure washer, bucket and drain bag that he fastened under the air handler. The difference between the thermostat that’s built into the air handler and room temperature had grown to around eight degrees, ie. I had to set it to 78 for a 70 deg house. The unit is mounted close to the ceiling in a very well insulated corner but that wasn’t what made it so warm at and around the unit. Following the cleaning the temperature spread dropped to about 2 degrees. I don’t know how much energy I’ve wasted and paid for by not having this done sooner.

Now I’m thinking this has been heating more like a smaller system and it wouldn’t hurt to wait until next heating season to decide what to do. Our house layout is conducive to good circulation and since the cleaning more warm air is getting to the kitchen shown by a smoke test and kitchen thermometer. A larger minisplit in the same location could work well. The Efficiency Maine incentive of us having to pay just 40% of the cost of an install plus the U.S. tax break makes it very attractive. Still that cost may be several thousand and still require occasional heat from the boiler. Of course we still have our boiler as an option as the wood stove’s replacement and, while requiring a bigger mental adjustment, it wouldn’t be terrible. The cost of replacing (or adding) and running the minisplit over the cost of running the boiler may not be cut and dry. I think a main advantage of spending on new comes from a increase in life span along with a new long term warranty.

 

[EatenByLimestone]

Out of curiosity, have you tried the old trick of blowing the cool room air out into the warmer house and starting a convection loop? The bedroom is right outside the room with the mini split.

 

[Max W]

Out of curiosity, have you tried the old trick of blowing the cool room air out into the warmer house and starting a convection loop? The bedroom is right outside the room with the mini split.

I haven’t. The minisplit fan and openness between the main two rooms promotes some circulation as it is especially after getting it cleaned. Blowing the kitchen air back through the passageway by the bedroom should do a good job of enhancing that.

The stairway wall behind the stove on the sketch is a foot or so off. It actually lines up closer to the center of the wide bedroom doorway so that room gets some good heat off the stove. I am surprised at how well the bedroom and bath heat in general when running the minisplit alone.

 

[bogieb]

Had our minisplit cleaned and what a difference. I had spray cleaned the condenser with a hose and routinely cleaned the the air handler filters but never had that indoor unit cleaned. While inside didn’t look bad after 8 seasons the fins, tubes and fan were dirty enough to apparently seriously limit air flow and heat exchange. The guy came with his spay cleaner, pressure washer, bucket and drain bag that he fastened under the air handler. The difference between the thermostat that’s built into the air handler and room temperature had grown to around eight degrees, ie. I had to set it to 78 for a 70 deg house. The unit is mounted close to the ceiling in a very well insulated corner but that wasn’t what made it so warm at and around the unit. Following the cleaning the temperature spread dropped to about 2 degrees. I don’t know how much energy I’ve wasted and paid for by not having this done sooner.

Now I’m thinking this has been heating more like a smaller system and it wouldn’t hurt to wait until next heating season to decide what to do. Our house layout is conducive to good circulation and since the cleaning more warm air is getting to the kitchen shown by a smoke test and kitchen thermometer. A larger minisplit in the same location could work well. The Efficiency Maine incentive of us having to pay just 40% of the cost of an install plus the U.S. tax break makes it very attractive. Still that cost may be several thousand and still require occasional heat from the boiler. Of course we still have our boiler as an option as the wood stove’s replacement and, while requiring a bigger mental adjustment, it wouldn’t be terrible. The cost of replacing (or adding) and running the minisplit over the cost of running the boiler may not be cut and dry. I think a main advantage of spending on new comes from a increase in life span along with a new long term warranty.

I clean the filters for my indoor heads every month. In fact, that is on my list of things to do today. I never do anything to the outdoor unit. I used my system for 2.5 years before having someone come out to clean the system. The guy was very impressed at how clean everything was - he said that most people don't even clean the filters. My installer stressed to me to make sure I do that. The guy that did the maintenance did spray down the fins and such with some sort of solution to do the final cleanings though.