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Ducted heat pump vs mini splits in spray foam roof attic

ALIVT | Posted in Energy Efficiency and Durability on

Hi All,
We have a high efficiency HTC mod con natural gas boiler w/ radiant downstairs and flat panel radiators upstairs. It does amazing in our 2200 ft2 Vermont house and our gas bills are no more than $130 in the coldest months, but we have solar now, and want to start to move away from fossil fuels, AND our second floor gets to the high 80s in summer with no AC. So we’re looking to add heat pumps. I want to start with the upstairs only – and I’ve read every article here that I can find. So it sounds like a most efficient option would be a one to one singular ductless mini split in one bed that we’ll hope will spread air around the top floor through open doors (3 beds and ~900ft). I was also wondering about ducted, but can’t find clear guidance. We have an attic that is not “conditioned” per se, but the insulation is R50 closed cell spray foam on roof underside. Could we do a ducted heat pump system with ducts to each bedroom in that attic successfully? It seems like it would be way more comfortable. There is no insulation on the attic floor – just on that roof underside. Any advice would be much appreciated, thanks!

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Replies

  1. Expert Member
    Akos | | #1

    That attic part of your conditioned space so it is a great spot for a slim ducted unit. Definitely a ducted unit over wallmounts.

    A single unit from there can feed a number of bedrooms easily without any of the oversizing issues you can run into with a wall mount in a bedroom.

    You don't need any fancy ducting. Some units come with a plenum adapter that take round ducts, you can do a simple home run with flex from ceiling registers in each bedroom. Return can be a single large filter grill in the hallway.

    I would also add a code min sized supply to the attic to condition it. This will avoid issues with sweating ducts in the summer.

  2. begreener | | #2

    Mr Cool has a DYI system now for that application called Versa Pro - compatible with upflow, counterflow and horizontal configurations.

    https://mrcool.com/versapro/

  3. paul_wiedefeld | | #3

    You want ducted for sure! Too many compromises with ductless.

  4. bon_vivant | | #4

    I have a similar situation. I added a heat pump, ducted, in my rafter insulated attic. I also added a small supply and return up there. It can't hurt and if there is a humidity problem up there this will help.

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