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Our home is a split level, with 5 floors - basement, den, kitchen, bedroom, master. Each of those floors is mostly open EXCEPT the bedroom floor, which is 4 separate rooms.

A HVAC contractor we got a quote from recommended a ductless system+heat pump with 3 indoor units. One on the kitchen floor, one on the bedroom floor, and one in the master.

What I don't understand is how a single unit on the bedroom floor would effectively heat or cool all 4 rooms on that floor. Most of those rooms have their doors closed all of the time, which would greatly hamper air circulation (and therefore temperature circulation). With the current AC, each floor has a vent, so it's not a big deal. But I don't understand how it would work with ductless.

Can a ductless system effectively cool a floor with multiple rooms if the rooms have their doors closed most of the time?

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With the doors closed and no evaporator in the room how is the cooling going to get into the room. In short it will not work with natural flow and the doors closed. On my 1930's home we have a 3 zone currently. The living room and the kitchen/ dining and the the master each have a unit. The other 2 bed rooms only get cooling / heat when the doors are open but since these only get used when relatives or grand kids are here we have not put a second unit in. I may add a second unit on the other side of the house for the 2 bedrooms and a small office but at this point it is not needed because we heated with wood for so many years we are used to having our doors open and that saves because we still use partial wood most of the winter as I am getting lazy LOL.

  • Ok, that's what my wife and I were thinking! So, I'll reach back out to the contractor and see if they can provide an updated quote that puts a slimline unit in each of the other bedrooms. – Matthew Aug 2 '18 at 0:45
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No, it won't work well. However, there's a compromise you could make, which is . . . semi-mini-ductless, you could call it. You still have the outside compressor, but inside, there's an air-handler and ducts, so you can have multiple vents, potentially one in each room.

One thing to watch for, which I wish I'd known more about, is that you end up being only semi-zoned, and in my house, which is sort of like yours, you can end up with wild temperature disparities. So the upstairs is hot, but the kitchen is cold. A single outside compressor can only heat or cool, so one of those places is going to have to wait until the other one is brought to the desired temperature. I'd strongly suggest going with multiple smaller outside units instead of one big one.

  • Thank you for the heads up! It sounds like we'll need to press the contractor to either add more indoor units, or figure out how to properly approach it. The option we had originally pushed for was central air + heat pump + hydrocoil to integrate with our current baseboard oil heat. – Matthew Aug 2 '18 at 17:00

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