Updating HVAC and Attic Insulation
I’ve just recently moved into a 1970’s house in Salem Oregon that could really use some significant HVAC and insulation upgrades…
The roof is framed with 2×4 trusses and barely has blown in insulation to the top of the bottom chord, and none of the junction boxes for ceiling ligts are detailed well at all so let lots of air through. In addition the duct work in the attic is neither sealed or insulated.
All this leads me to want to start with removing all the ductwork in the attic and replacing it with a mini split while I air seal and insulate the attic properly. I could easily put a single head at the top of the stairs, but there’s 4 bedrooms upstairs and I don’t think I would be able to keep them all comfortably warm in the winter this way. I don’t want a multi-head setup so are there other options that would make sense like a ceiling cassette that is ducted? If I’m interested in adding an HRV would it be a good idea to try to tie that into a ducted mini split system?
Couple other notes just in case – the current system is a 4 ton heat pump with the air handler in the garage that serves both upstairs and downstairs. I plan on doing a manual J that uses a leaky envelope and r-11 in the walls and whatever amount of insulation I decide to add to the attic. My goal is to eventually get rid of all the old duct work and the air handler in the garage but due to budget constraints I think we’ll have to keep the downstairs HVAC for at least a year. I’ve just moved from a very mild winter climate (bay area California) where getting the sizing on my mini split there would have meant just wearing a light sweater indoors, whereas here in Oregon I’m much more concerned that if I get it wrong (I’m thinking just by having airtight ducts 3ton heat pump would be plenty, but will do a manual J to confirm) the bedrooms will end up like ice boxes.
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Insulated and sealed attic ducts get you the room by room distribution you want, so I’d keep that setup with upgraded ducts. I suggest searching GBA for articles about creating a conditioned attic, but there are other methods too.
Sizing heat pumps is tricky since their output varies based on outdoor temperatures. Depending on the model, your 4-ton unit might have lower heating capacity than a new 2 or 3 ton unit, and that’s before the insulation upgrades.
Ductwork in the attic can also be buried in insulation if it's done right, and a mechanical closet in the garage can be made airtight if it doesn't house any combustion equipment. Air sealing the attic floor, attic ducts, and adding insulation should be your first consideration as it is nearly always the "low hanging fruit" where you get the most bang for your bucks.
Thanks Peter, it sounds like you're advocating for keeping the equipment and just trying to lower the duct work while air sealing it while I do the rest of the attic work? That certainly would be a lot friendly on my wallet, the only concern I have with that I suppose is I don't want to have to revist the attic again once I do this project this year.
Unfortunately I don't think I could box the current air handler into it's own closet since it's less than 2 feet from the steps to inside the house and so close the the water heater I would have to put the water heater into the proposed closet which would then prevent us from parking in the garage.
You've sparked an idea though of expanding the current duct work chase to take up part of our spare room and make it a mechanical room. I think I could keep the ductwork somewhat simple if I just have one return in the upstairs hallway and keep the runs to the rooms short by not putting the supply vent at the window (from some reading it seems like supplies at windows aren't as crucial with even mediocre windows?).