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Old 07-07-18, 12:08 PM   #1
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Default Reasonably conventional HVAC options

Hey folks, I've been here for a long time, not much in the way of posting, but a real fan of heat pumps. Put a single head mini-split (Mitsubishi Hyper-Heat) in my downstairs (open concept Cape Cod) a few years ago and absolutely love it. Takes care of the shoulder season heating before the woodstove kicks in full time, and does a great job of cooling the downstairs.

Trouble is, cold air doesn't rise. So, when the dog days of summer arrive, the upstairs (3 bedrooms, hall, and bathroom) absolutely roasts. In winter, life is good, as heat rises, and convection handles the upstairs pretty well.

I have wracked my brain for several years trying to figure out how to efficiently get a heat pump to handle the upstairs. It's just me and my wife, so the majority of the time, the two spare bedrooms are closed to reduce HVAC loads, but I'd like to incorporate them into a complete solution.

So, the issue is, I have no duct chases. The house was built with electric baseboard (ugh.) I am reluctant to put a wall-hung mini-split head in each room, as some of the rooms are quite small. The entire heating/cooling load of the upstairs is 9500/5500 Btu/hr, respectively. Thats basically one head for the whole upstairs.

Any ideas besides hang one head and leave all the doors open? I've considered multi-heads, ceiling-mounted, ducted units in the attic (again, ugh.), etc. They all seem lacking for such a small heat load.

I did do an ACCA Manual J calculation, and since that time, I've replaced all the windows and doors, and re-sheathed the house with new house wrapping, so the thermal performance has only gotten better.

Appealing to the crowd for options I may not have considered. What do you think, group?

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Old 07-07-18, 08:23 PM   #2
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Ok so you are facing the same type of problems encountered in the passivehaus homes. Not enough heat load is a good thing, but for comfort and quality of life, you will have to find a way to ventilate properly. That's the long and short of it.

When I was in the house that wouldn't heat or cool easily, I put a heating unit downstairs and a cooling unit upstairs.
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Old 07-07-18, 08:33 PM   #3
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If it were me I would go one of two ways. Install a dual or usually triple head condenser and one small unit in each room. The other option would be two of the smallest independent units you can get.

I would lean towards option one and some brands like LG you will end up with a 3 unit condenser but you only have to use 2. Then you get a spare hook up for somewhere else if needed.

I like minisplits but they are not a replacement for traditional forced air systems as they only cool one room. Putting in one system upstairs in your place and leaving the doors open isn't a functional solution as there is no airflow. I don't see a traditional forced air system that would work in your application other than a fur down like apartments have but they are very inefficient noisy and a very difficult install.
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Old 07-09-18, 08:52 AM   #4
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Mount some fans to the ceiling for airflow?

To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...
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