Mitsubishi Mini Split: HVAC person said won’t head 500 sq. ft. with 12 foot ceilings
Hi – I am building a ranch in Zone 5 that is 84×26 with 12 foot ceilings. Floor trussses and roof trusses. Attic will have close cell under roofing deck and in bays blown in on this new construction. I understand 12 foot ceilings require more BTUs but we wanted a barn and more space feel as we downsize.
I had been considering the several ceiling units as their seems to be three options with Mitshubishi – one is a ceiing cassette which you can see with a modern look (not the wall mounted unit) Next is a unit like the cassette except you don’t see it and you can add ducts to it. The 3rd is an air handler your mini-split connects two. I was looking at maybe a blend of 1 and 2.
The HVAC person who was there today said a mini-split will not handle or heat this central room, which is a open space kitchen and entertainment area. He is pushing to put a boiler with a air handler in the basement which has 8 foot ceilings. I complained that the basement is not conditioned or insulated and I would not want to make a mistake of putting this system in the basement, which is a walkout and the exterior was sealed with Poly Wall. The HVAC person said they would cost a ton to put in ( I was going to buy online) (Don’t see the complication with no ducts) HVAC person also said when the temperature gets down to zero they are worthless, but from what I read, they don’t get the BTUs the colder it gets but they don’t not give heat. We will also have a new Pacific Energy woodstove and our plan was to add radiator heat with our propane boiler later on as the mini-split would be mostly for air conditioning long term. I would also think the wood stove would heat the house on real demandng days.
Has anyone used Mitsubishi Mini-splits and are they a pain to clean a couple times a year and how did you find they performed. The houses today are so air tight and insulated – Thank-you in advance.
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So, did they run a manual J load calc before they gave their opinion? Bet they didn't ;) Which means find another HVAC contractor. You should run your own load-calc at coolcalc.com to be informed.
I don't know the max ceiling height for the mitsu in ceiling units, I don't see a discussion in the manual at http://meus1.mylinkdrive.com/files/MLZ-KP-NA_Install_RG79Y948H01_03-18.pdf I doubt that 12 ft ceilings would matter, in a tight house, although I suppose there is some risk for the heat staying high (stratification?)
If you do go with the ceiling units, keep in mind that your ceiling needs to be both flat and level, since the face of the unit seals against the ceiling. There's only 1/8 inch tolerance on the unit being out of level, and if the grille doesn't seal then lots of dust gets on the blower wheels and it is a 2 hour job to clean them. More on that here: https://www.ecomfort.com/Mitsubishi-MLZ-KP09NAG/p82597.html
Definitely BTUs drop off at some point, depending on outdoor unit, but it's all well documented. Backup heat sounds like it would take care of that anyway.
With the ducted unit, keep in mind that you need substantial space under the unit for service, that really tripped me up in thinking about locations. I think it's something like 2 feet? So they really have to go in a conditioned attic space or just above a ceiling access panel.
Thank you James - It was very nice of you to take the time to address my questions.
You are correct that they did not do any calculating and it was a visual. It was their first time in the home as they were their to look at plumbing. S eems I am finding you call guys for rough in plumbing and they all default to HVAC. The house is literally a rectangular box - There are open floor and roof trusses so snaking pipe and wiring is easy. Everything is on one floor but today every trade seems to make everything a big issue. Had one guy not want the plumbing job because the air vents to the drains would require him going above 8 feet to 12 feet. I told the guy you can walk up the stairs to the attic and drill down if you don't like ladders and that was of no comfort to him. One guy only uses PEX and the next guy will only do copper. No one will use Wirsbo and every plummer uses VEGA or something like that in Connecticut. I did the calcs and with 12 foot ceilings, EComfort was recommending a 12K BTU Mitsubisi unit and I know they go much higher, so I was puzzled when the guy said it wouldn't heat the space and asked what am I going to do with all of the units afterwards as I would be doing the job twice.
The walk up attic space where the center is like a bowling alley, has open space on the left and right side of the center for ait handlers and lines - the HVAC person said they would not put anything in this attic space which I mentioned will be foamed in R49 or better on all sides under the roof deck and gables. There are Anderson A series double pane windows on each gable end. As you pointed out, there would be plenty of space above and below if we used the ducted unit. The space between each roof trusses is 24 inches so if I put any unit in the space it would have to be able to fit thru the 24 inch space.
My experience may be useful. I'm in zone 6 (Maine). Our kitchen/ dining/ living space is about 900-1000 square feet, with 13' ceilings over most of the space. A single Fujitsu 12RLS3 H heats it just fine. R70 roof, R42 walls, R16 slab, .59ach50.
A single head, ceiling cassette or slim duct will definitely work. Get an engineer to do the design. Energy Vanguard is popular and if they can’t do it, will make a recommendation. Have the hvac contractor install per the plan.
With a walk up attic and hvac in the attic you will need a thermal barrier on the foam. That would be drywall or the paint approved for that foam.
Thank-you - very comforting to hear the positive responses on the mini-splits. I was thinking of covering the foam attic roof decking with rock wood which doesn't burn - it's a thought but not sure if anyone else has done this before. I looked up the Fujitsu 12RLS3 H - WOW that has over a 26 SEER. I had only been looking at Mitsubishi so far - it seems many prefer Fujitsu. Would be good to hear why some made the choice. I have to pass along on the house I am building, I put Siga tape around the perimeter to seal the foundation cement, sill plate to sheathing. When I contacted SigaTapes.com, I was going to order the tape and brush on glue primer when the contact at the company said there is a new Siga tape that doesn't need the primer. I took the advice and ordered the tape which I found feels like felt cloth. I got to tell you, this stuff is a home run - went on easy and it sticks great to the cement. The tape back has two peel off down the middle seams so you can apply 1/2 to get the tape in position then peel the second half. I was so impressed I had to pass this along. I am not plugging for SigaTape but the order came in a couple days. OK back to the mini-splits
James. I think most people opt for Mitsubishi or Fujitsu based on the reputation of the dealer. Both brands get good reviews.