What do you think about an upstairs wall unit?

14 years ago

It seems that homes that have an upstairs (especially 1-1/2 story homes in which the roof is the ceiling) have a hard time keeping cool, since there is so much insolation on the roof, and warm air rises. I remember in my old house, I would have to set the thermostat quite low to get the upstairs at a decent temperature, but as a side effect, the downstairs would be too cold. And on hot clear sunny days, it was impossible to get the upstairs cool enough (fortunately my upstairs was the game room, so I didn't need to be there.)

Anyway, my sister's house has a similar upstairs design, and she had a second HVAC unit put in. The beauty of this is not just the extra cooling capacity, but the fact that it runs independently of the main unit, so that the main unit can be set to properly maintain the atmosphere of the downstairs, while the upstairs unit can be set for its atmosphere as well.

For my new home, I will have some rooms with cathedral ceilings, and the warm air can rise up, and I could care less about it (I will have fans, but they will be at about the same height as if they were in a 9' ceiling room.) There will be a 2 bedrooms and a bathroom upstairs (about 350 ft^2 total), and it seems like I should get a single small, wall mounted booster unit for those 2 rooms (e.g., 1/2 or 1 ton.)

I've seen these types of units in Europe. The condenser unit is simply bolted onto the side of the building, and a small evaporator unit and fan on the inside. As I understand it, they are becoming more popular in the USA, as some folks don't want to hassle with a window unit.

What do you think? Has anyone done something like this? I know that some folks have gotten complete central units for the upstairs, but what about for a situation like this?

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Comments (6)

swampwiz
Original Author
14 years ago
I was wrong about the location of the evaporator. It seems to be outside as well. Only the fan is inside (which gets air blown outside to get cooled by the evaporator.)
energy_rater_la
14 years ago
mini split units.

condensing unit is outside air handler units are installed on interior walls.

I have to admit I'm gettin a kick out of your thinking.
you would have a ball with my software!

I'm not a big fan of multiple units on average sized homes.
when properly designed on average sized homes two stories can be heated and cooled by a single unit. properly sized
with zoned dampers. this is a zoned system. multiple t-stats one per zone..one unit.

visit www.buildingscience.com
google unvented attics (should have put this in earlier post..sorry)
also read studies for your location.

where are you located?
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creek_side
14 years ago
You are describing my current home. It is heated and cooled by a single heat pump. No zoning. There are baffles in the main supply ducts leading to each floor. These require manual adjustment twice a year when the system is switched from heating to cooling and vice versa. No zoning needed.

Zoning is expensive and an added complication. It also can result in inefficient operation at times. If you can do so, avoid it.
energy_rater_la
14 years ago
Zoning is a great thing when done correctly.
Motorized dampers (not manually adjusted dampers)
adjust as zone calls for more air.

folks who have a properly installed zoned system
and the folks who can do these installs have quite
a different pov.

the two units for "zoned" system comes from those
who can't, or houses not designed for zoned systems.

then you get the old story..Yeah, but if one unit goes
out you still have a cool place to go.

its an option.
creek_side
14 years ago
I just had an extensive discussion with the owners of an long established HVAC business regarding zoning. Their take was avoid it if you can.

Zoned systems cost more to install than non-zoned systems. They have more components to go wrong, and they have to have a provision to dump the excess capacity back to the return when only one zone is calling. That results in additional cycling over what would occurred if the entire house was a single zone balanced with manual dampers.

It can also result in short inefficient run times when only a single zone calls.

Multiple HVAC systems for a house are whole 'nother story.
swampwiz
Original Author
14 years ago
I think the combination of having a simpler main system, and having a completely separate auxiliary system (in case the main one goes down) makes the most sense to me. Also, the upstairs is going to be unfinished for a few years in any case, so I can simply add the auxiliary unit when the upstairs would be finished.

What do you think about an upstairs wall unit?

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swampwiz
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energy_rater_la

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What do you think about an upstairs wall unit?

Comments (6)

swampwizOriginal Author

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