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Mini split whole floor question

xman1111 | Posted in General Questions on

Hey guys, hoping i can get a litte advice.

I live in Vancouver, Canada in a 3 year old 1430 square foot 1/2 duplex with floor heating (no ducts). Our portable air conditioner isn’t cutting it anymore and we are looking into getting a mini split.

We were really mainly concerned about cooling our room but it’s pretty expensive to just do one room. We were thinking about doing a single head above the stairs to try to do the whole floor, then the expense doesn’t seem so bad. It would be nice because our daughters room and our loft (which is currently the dog pen) would also get cooling. I am worried about spending the money only to find out that we were still hot in our room at night and the loft is ice cold. We just had a 45 degree heat wave and it was about 33 degrees upstairs in our house without using our air conditioner.

Our neighbour just got a Daikin 18,000 BTU single unit and placed it upstairs and they told me that it gets uncomfortably cold upstairs and perfect for downstairs. That being said, i don’t know them that well and haven’t been inside their place. It is a little different layout than ours as well.

The quote i got was for a 18000 BTU Lennox mini split with 12 year parts warranty and 5 years labour warranty from a very well respected local company.

I attached a pic of our layout, wondering if anyone had the time to comment on it.

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Replies

  1. Paul_Iowa | | #1

    Your whole downstairs will stay cool. I live in Iowa and it's hot and humid here. Our first floor is about 1400 square feet, and 2/3 of it is solid masonry. I can cool the downstairs with a 12k btu Fujitsu floor mount unit. The big room where the unit is located (about 550 square feet, not the solid masonry portion) stays exactly at set point, while the other 2/3 portion of the house (the solid masonry part) stays about 4-5 degrees above set point, but with completely manageable humidity. The floor unit is mounted such that it is not pointing toward the opening going into the solid masonry portion.

    Don't know about Lennox units, but at least with Fujitsu units there's a decent performance hit between 12-15k and their 18k unit. Perhaps your best bet is to downsize to a more efficient unit?

    1. xman1111 | | #3

      thanks for your response. they actually speced a 12,000 BTU unit but said they would upgrade us to an 18,000 unit. I will have a read of the specs to see if the 12,000 would be better, still not sure on the Lennox.

  2. irin | | #2

    I’ll share our experience - hope it will help. This site was a tremendous help when we tried to make our decisions in a hurry and all HVAC people were unhelpfully offering to install the same large replacement AC system into the unconditioned attic :) Good that we did not listen :) We live in Maryland and it is humid here and we have plenty of 95F days during the summer. The house is a 1800 sq ft cinder block raised ranch built in 50’s- about 1000 sq ft on the main level and 800 sq ft in the finished half basement level. The upstairs is split evenly - large open living-kitchen area (500 sq ft) and three small bedrooms (150, 100, 100) and two tiny bathrooms, all their doors open into a narrow L shaped hallway. We used to have a 3 ton! air conditioner with air handler and ducts in the unconditioned attic plus gas furnace in the basement area with it’s own ducts through the floor. The AC died a month and a half ago, beginning of June. We replaced it with 18k hyperheat Mitsubishi minisplit with single floor mounted air handler head that was placed in the living/kitchen area. We did not have much choice for the location - it is on the outside wall and does not face the hallway leading to the bedrooms. Minisplit installation was kind of an emergency - the temperature was already in the 90s. We planned to later add a second small 9 or 12k system - either multi split or ducted unit - to the bedroom area. Now that we are through a hot June and most of the July with this setup I am very happy to report that, miraculously, for 1/3 of the cost ($230 bill last year, $86 this year for the same period) this 18k unit cools down our whole house, including the bedrooms and we actually do not need the second system. There is some temperature difference throughout upper level - the kitchen/living is coldest, but not icy cold, perfect for daytime active activities :) the bedrooms are a bit warmer, but not stuffy and very comfortable to sleep in. We used the “set it and forget it” approach - the system runs all the time on the same settings. I initially spent four days experimenting and adjusting the thermostat settings (we did not install the wall thermostat, so it is only whatever the air handler measures). I ended up setting it at 68F, seems low, but the thermometer placed on the table in the living room measures 71 F most of the time and about 75F in the bedrooms. The relative humidity is 50% throughout the whole area, feels like crisp fall air :) The downstairs rec area is cool too, I did not measure , but it is half in the ground, so it was always comfortable in the summer. The system is very quiet, both outside compressor and inside unit, we keep air handler on low fan settings (2 out of 5), you can barely hear it in the living area (much quieter than old ducted AC) and can not hear at all in the bedrooms, but it moves large quantities of air, you can feel it if you stand in front of it. We got floor mounted unit and I set it so it blows both up toward the ceiling and down towards the floor. There are two things that we do that help to redistribute the air - in the evening, before going to beds, I open bedroom windows (just a tiny crack) for about 15- 20 min and at the same time switch on exhaust fans in both bathrooms. This creates a noticeable movement of air from living area through the hallways towards bedrooms in addition to getting some air from outside. This has always been my habit, I like to have some new air in bedrooms at bedtime. Also, we do not close doors to the bedrooms completely. We now plan to install some ceiling fans and try to use just the minisplit for winter heating and, if successful, - get rid of the old gas furnace that currently occupies half of the basement :) I’ll report how that goes :) In conclusion: based on our experience - yes, you can cool the whole area with multiple rooms with just one air handler head. They are powerful and efficient and able to move large masses of air very quietly. Your floor plan is actually more “open” than ours since there is no narrow L hallway, but you might need also to take into account your personal habits and other details - do you keep doors always shut or mostly open, do you have ceiling fans or exhaust fans in any of the rooms, etc. Good luck and please keep us posted!

    1. xman1111 | | #4

      thanks for taking the time to write that, it gives me some hope. this has been the frustrating thing, some say it works good, some say no way, not a chance. my neighbours are doing it and say it works great, i guess i am just looking for a little reassurance before spending the money. We have a ceiling fan in the loft and in our bedroom that we use quite a bit. We also have an exhaust fan in the bathroom. Door open or shut doesn't matter, we will do whatever it takes to move the cold air around. That is really good news though, was losing hope.

      1. irin | | #6

        You are very welcome. You will be happy with minisplit :) I had the same frustrations while researching it and getting various AC estimates. The professional HVAC people do have a bias towards installing what they have experience with, preferably replacing any system with identical or very similar system. When starting from scratch as in your case or switching to a different system as in ours they were very unhelpful, three HVAC estimators told me that minisplits will not work in our case. Their arguments were “minisplits are only good for new airtight houses, your house is too old” or “ you have now four air registers in the ceiling of the living/kitchen area, so you need more than one air handler” etc. All this turned out to be wrong. It actually performs much better than we expected even in our old leaky house. In your case 12k or even 9k system might work better since your house is new and supposedly has better insulation. Your heating bills should help you estimate how well it is built :) By the way, are you considering cooling only system or do you plan to have cooling/heating one? The difference in price is minimal but the cost of heating with minisplit is supposed to be much more economical compared with electric resistant.

  3. Expert Member
    Akos | | #5

    I'm using a similar setup in a couple of two story rental units and it works reasonably well.

    With a reasonably well sealed new construction you'll be able to cool the place provided you keep the doors open. The open den area will generally be colder than the rest. I would get a programmable remote/thermostat so you can crank up the AC at night time when there is nobody downstairs or in the den.

    A 2nd floor unit also do a good job of cooling the main floor.

    18000BTU seems a bit on the large side for that space, 12000 is probably closer to right size.

    Instead of a wall mount I would go with one of these:

    https://ashp.neep.org/#!/product/29607

    They are pretty large and don't fit between standard rafter spacing, but could be mounted bellow the ceiling at the top of the stairs. You would box around it with some 1x10 and trim painted white to match the ceiling.

    The nice part about this unit is the knockouts on the side. These are for jumper ducts, so if you find the bedrooms still uncomfortable down the road, you can connects ducts to these and run it to the bedroom.

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