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jasonko

Hot 3rd floor loft - ductless split, better ducts?

jasonko
10 years ago

I'm evaluating whether to get a ductless split or if another solution is available for a hot 3rd floor loft space. House is in Northern Virginia with hot summers.

I have a third floor loft, adjacent to an attic space and below the roof, that gets extremely hot. House has an open staircase from the first floor, so the loft gets rising heat throughout the house and radiant heat from the roof and attic.

Loft and 2d floor are currently served by a 2.5 or 3 ton heat pump that sits in the adjacent attic along with a lot of the duct work. Heat pump is 7 years old. The duct work generally seems insulated, straight, and properly installed in the attic space. The loft has 3 vents and 1 return in it to compensate for the heat, but still extremely hot in the summer. There is another return on the 2d floor and the rooms down there generally have one vent.

Options appear to be to better seal and insulate adjacent attic, evaluate duct work and insulate or otherwise fix issues with the duct work, get a ductless split for the loft, put in larger HVAC system, or some combination. A window unit would not work for the space, unfortunately.

Is a ductless split an option that makes sense? - it would appear to almost certainly work, but would be compensating for the overall poor design of the HVAC system and loft build. My instinct is that it doesn't make sense to put a bandaid over something without first fixing the real problems. Would sealing up the attic make a significant enough difference considering that hot air within the house is always going to rise into the space through the open staircase?

It's obviously hard to tell without seeing the house, but any thoughts would greatly appreciated!

Comments (5)

  • ryanhughes
    10 years ago

    You definitely don't want to oversize the current equipment to compensate for a loft space, which by its nature will be hard to condition relative to the entire upstairs space. An oversized unit would make matters worse by running shorter cycles (less dehumidification and more importantly, less conditioning of the space that has a higher heat gain relative to the rest of the upstairs).

    First: Has a load calculation been done on the upstairs to determine the capacity needed for each room (including the loft)? Airflow balancing is likely in order to improve airflow to the room, which may require larger supply ducts. But you still may not be comfortable all the time. I'm assuming the thermostat is in the main hallway or master bedroom, nowhere near the loft. Zoning is not really an efficient or feasible option with that small of a space and that large of a single-stage system. You could try running the fan in the "on" position for air circulation. You could also install a thermostat with averaging capabilities to average the temp in various upstairs rooms, including the loft.

    I really like the mini-split option. Mitsubishi mini-splits are VERY nice, and I think this is a great application for one. The inverter systems are variable capacity, so the output will match the demand of the loft.

  • jasonko
    Original Author
    10 years ago

    Thanks for this. I have not done a load calculation, we bought the home after it had been extensively remodeled and expanded. I assume that a load calculation was done when they built the loft, but of course, that's only an assumption. The thermostat, is just like you say, in the master bedroom, nowhere near the loft and considerably cooler in the summer.

    With larger ducts to the loft, there's a chance it would help, but no guarantee - what would replacing ducts cost? something like 20 feet worth?

    Thanks, everyone seems to like ductless splits, except for a few folks! I'd be fine with it, if it was about 1/2 the cost.

  • ionized_gw
    10 years ago

    I am a fan of mini-splits, but it appears that the current central system is very close so ducting revisions would be simple and inexpensive. It is well worth investigating that.

    Evaluating the whole house with special emphasis on the relationship between that room and the attic would be a good idea. Insulation and air sealing are the most economical things that you can do. If you can over-insulate that room, it might be cool enough relative to the rest of the house.

    If the house is new to you, you might want to get a non partial energy rater to help you identify the low-hangning fruit for efficiency improvements and advice on fixing the hot room. Start at Resnet.

  • jasonko
    Original Author
    10 years ago

    Thanks, I had an energy audit done early and the attic was an area of concern so insulation was added to the walls adjacent to this loft space and elsewhere, although further spray foam sealing is probably necessary. One large area that is being fixed now was the door which is 3X4 and just plywood. My wife wants the temperature fixed in the loft, so I don't think I can convince her to insulate more, fix the duct work, and test this summer, but I think I can convince her to insulate more and fix the duct work if she wants to get the split, so that seems to be the direction we are headed!

  • Kevin_365
    10 years ago

    This situation is tailor made for a ductless split. That way you can control the zone that you need cooling (lofts and attics tend to be hotter as heat rises) without making the rest of the home uncomfortable from over cooling. The other advantage is you can leave the system off until you use the room as you can cool much quicker with a mini split then a large central system saving you $ from cooling a space that's un occupied.

    Here is a link that might be useful: Mini splits

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