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Community and Q&A

Adding A/C to 1918 built home

bforney | Posted in Mechanicals on

My husband and I own a 1918 built foursquare home. We currently use a single 8000 BTU window A/C unit to moderate the worst of the summer heat in our zone 4 climate (Minneapolis). We have discussed installing a split A/C system or small duct central A/C system on the first two floors our home. I think I have a good grasp on the split A/C systems but know less about the small duct systems. I like that the small duct systems have less impact on the look of the house. From what I understand, attic installations are fairly common with these.

Our attic is unconditioned with 1-2 inches of closed cell foam on the floor for air sealing and insulation and then loose fill fiberglass above it for insulation. The total R value is 50 in the attic. We were really deliberate about our strategy for re-insulating and air sealing our attic a few years ago. I’m concerned that an small duct installation in our attic will break the air barrier and reduce the effectiveness of the insulation and also allow moisture into the attic during the winter creating frost.

A few questions:

– Is my concern about breaking our air barrier and reducing the effectiveness of the insulation likely warranted?

– Can the small duct systems be installed completely within the conditioned space of the home (except for the compressor unit), such as in an unfinished basement?

– Are there other system types one recommends considering beyond these two systems?

– Are there small duct systems that can also be used with an air exchanger to help with humidity and fresh air control during winter months?

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  1. GBA Editor
    Martin Holladay | | #1

    The only advantage of high-velocity, small-duct air conditioning systems is that fact that the ducts are small. In all other respects, these systems are less desirable than other options.

    You gut instinct concerning the installation of ductwork and air handlers in your unconditioned attic is correct: you don't want to do it.

    Yes, it's possible to install an air handler and ductwork in your basement. That's a better location than an unconditioned attic.

    I think that the best solution in your case is to install two ductless minisplit units -- one per floor.

    If you want to install a ventilation system, I advise you to keep your ventilation ductwork separate from your heating ductwork or cooling ductwork. For more information on ventilation systems, see Designing a Good Ventilation System.

  2. STEPHEN SHEEHY | | #2

    Brian: Minneapolis is in USDA plant hardiness zone 4,(higher numbers are warmer) but climate zone 6 (higher numbers are colder). I wish the zones were uniform as the two scales can cause confusion for some people. Not me, I'm in Southern Maine, zone 5 in both categories.

  3. STEPHEN SHEEHY | | #3

    Deleted double post

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