Review my heat pump sizing?
Hi!
I’m looking for some help figuring out my heat pump situation. The basics of my home are that I’m located right on the border of climate zone 5 and 6 and live in a rural 1100 sqft (+1000sqft finished basement) bungalow. The home is 12 years old and fairly tight. The heating for the home is radiant in-floor heating (staple-up on the main floor, in-slab in the basement) off a propane boiler. There was no cooling in the home when I moved in 18 months ago.
I had a 3-zone 30k, BTU Mitsubishi Hyper-heat heat pump installed a year ago with 3 indoor heads- a 15k wall unit in the basement, another 15k in the main upstairs living area (kitchen/dining/living are all one open concept ~550sqft space), and a 6k head in the master bedroom. The two other bedrooms on the main floor were left without heads, with the thought being that we could heat and cool the rest of the spaces and trust air movement to make those spaces comfortable.
That previous sentence has turned out to be untrue, at least as far as the tiny occupants of those bedrooms are concerned. We’re basically unable to use the heat pump as our winter heat source and have to just continue using the propane as our primary heat in order to provide reliable heating in those spaces, and in the summer those rooms are a little warmer than we’d like.
I’m trying to figure out the best way to add heads to those rooms (each about 110sqft) in the context of my existing infrastructure. I’d like to use the heat pumps for cooling in the summer (note that the basement rarely if ever requires any cooling) and as my primary heat source in the winter (so would be running all the upstairs heads, and running the basement head less to try to keep that space tolerably warm).
My thought is to add a two-zone 20k Mitsubshi hyperheat outdoor unit and 6k heads in each of the unconditioned bedrooms, and then reconnect the heads as follows:
Existing 30k outdoor unit- 15k main living space head, 6k bedroom 1, 6k bedroom 2
New 20k outdoor unit- 15k basement head, 6k bedroom 3
I’m just struggling to figure out how this will align with the heat pump min/max capacities…will that new 20k outdoor unit be running very inefficiently in the summer if I’m asking it basically only operate one 6k head at minimal capacity?
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Replies
My 2 cents: Indeed, running a 6k unit alone with a big outdoor unit is not ideal. I would group all bedrooms on the same unit.
Ideas: replace the 15k unit in the basement by a smaller one if sufficient, replace the 6k unit in the bedroom by a 12k ducted unit feeding the 3 bedrooms from the hallway.
Or: disconnect the 6k unit from the existing 30k, install a 12k ducted for bedrooms 18k unit with 3x6k for the bedrooms (check possible combinations for the 30k unit).
Thanks for the thoughts. A single unit with ducts for the bedrooms had crossed my mind, but seemed a little daunting as far as adding ducts to a house without any...but I guess messing around in the attic isn't that much of an obstacle here. Could I retain zone control in each bedroom with some kind of switchable fan system in the ducts? I assume so.
If the bedrooms are adjacent, you could have a single 0.5-1 ton unit in one of the bedrooms, and an EC motor blower in a short duct that brings air between rooms. Noise might be an issue.