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Help! My house has its HVAC ducting outside the envelope

MitchellT | Posted in Energy Efficiency and Durability on

In my area in Central Virginia, it is ‘fashion’ to install HVAC duct work outside the controlled envelope of living space. First floor ductwork is in the crawlspace; 2nd floor ductwork and the upstairs air handler is in the attic. Everything I’ve read in FineHomebuilding warns against this, but apparently local builders aren’t reading FH. So, what am I as a homeowner to do within reason to remedy this situation? What is the most cost-efficient course of action short of creating new duct chases throughout the house?

Thanks –
owner of a gas guzzler home built in 2003 🙁

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  1. GBA Editor
    Martin Holladay | | #1

    There is no inexpensive way to fix this problem. However, the best solution is to convert your attic to an unvented conditioned attic, and to convert your crawl space into a sealed, conditioned crawl space.

    This work will have many benefits. In addition to bringing your ductwork within your home's conditioned envelope, the work will lower the likelihood that your crawl space will develop mold problems, will lower your energy bills, and will probably make your home more comfortable.

    For more information, see these articles:

    Keeping Ducts Indoors

    Building an Unvented Crawl Space

    Creating a Conditioned Attic


    It may be helpful to break it into smaller projects and tackle them one at a time.

    I would start with the sealed crawl, as Martin says it has a lot of benefit from humidity control as well as being a good stop against stack effect.

    Second go after the ceiling penetrations, remove the grilles and caulk all the duct penetrations in the ceiling as well as the light fixtures and any top plates you can get to from the attic.

    Then look to see if it would be possible to build an insulated box around the air handler with foil-faced poly-iso foam and wrap all the ductwork outside of this box with R-8 duct wrap. if there is enough room in the attic to do this you could work your way back from the perimeter towards the insulated box and wrap up by adding a layer of cellulose to everything and caulking the duct penetrations leading out of the box with flame-stop canned foam.

    If this is not practical you will have to fall back to having someone with remodeling experience spray foam the underside of the roof with all the complexity, odor, and cost that will entail.

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