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Community and Q&A

Heat Pump for a Small House

Stan_886 | Posted in General Questions on

Hi All,

I have a 1050 sq ft house. It has 3 bedrooms, each about 110 sqft. I currently have a 36000 BTU gas wall heater and two window ACs totalling 18000 BTU. I live in San Francisco Bay Area, California, where my summer temps don’t usually go above 95F (35C), while winter temps usually don’t drop below 36F (2C).

I had one contractor do a “wild guesstimate”, and talked about an 18k BTU Heat Pump. General calculators online put heat load at around 30k, while cooling at around 20k.

If i take a mini-split, the smallest consealed ducted indoor unit available is 7k from Fujitsu, Daikin or GE. Even 6k wall units seem like a gross overkill for 110sq ft bedrooms.

Smallest 4 zone ducted mini-split system i could find is a 36k BTU system, which seems a bit much as well.

What are my options?

1) I’d like to have a zoned control for every room. Ideally 4 different zones.

2) The system could be a little bit larger than needed. I plan to build a 500 sq ft addition. Bedroom sizes stay the same.

In my case i keep coming back to a traditional split heat pump with air handler, ducts and damper control.

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  1. paul_wiedefeld | | #1

    "In my case i keep coming back to a traditional split heat pump with air handler, ducts and damper control."

    That's what you want. Minisplit is a bit of a meaningless term now: It can be a ducted "minisplit" (like Fujitsu or Mitsubishi's high static air handlers) or "traditional" (from the same manufacturers or Trane/Carrier/etc). Very little difference.

  2. aunsafe2015 | | #2

    "1) I’d like to have a zoned control for every room. Ideally 4 different zones."

    This is going to be very challenging for 110 sq ft rooms. Maybe an expert will have better advice, but if I were you, I'd probably just get a system where you can use something like an Ecobee thermostat with remote sensors, and put a sensor in each room, and either average them or tell the Ecobee which sensor will control the system at different times of day.

    The other possibility is getting something like a zoned 2-ton Trane XV18. But a 110 sq ft room is not going to have the supply duct size to create a "voting" zone. So rather than having 4 zones, you might be able to have two zones. Living space + 1 bedroom on 1 zone, and the other bedrooms on a second zone. Even then, you probably need to oversize the ductwork to get enough capacity for both zones to be "voting" zones.

    The other challenge with this solution is that, although not technically difficult to achieve, it's definitely beyond the scope of what an HVAC contractor is dealing with on a regular basis. So you'd probably get most of them telling you not to do it (largely b/c they simply don't like doing projects out of the ordinary). Or, you might get a poor installation. In other words, with zoning, you need to be extra sure your contractor is very competent. And that's easier said than done.

  3. Expert Member
    PETER G ENGLE PE | | #3

    With a house that small, there's not much need for separate zones. You won't see any meaningful energy savings by setting back some rooms and heating/cooling the others, and zoning would make the system design far more difficult and expensive (as you are finding out). At that size, a single ducted heat pump or minisplit would more than suffice for the entire house and you might as well just keep all the rooms at the same temperature. Simple, energy efficient, easy to maintain.

    1. exeric | | #4

      +1. If a simple plan will work for a particular situation, then that's the way to go.

  4. walta100 | | #5

    4 zones in 1025 Sqf seems a bit much.

    Assuming all the walls and windows are of about the same quality your rooms are going to be about the same temp without zoning.

    Zoning can be useful when one room is very different than the rest, like a sun room that is all glass that may need more heat at night and less heat on sunny days or when you have a second story that tends to be a different temp than the main floor.

    If for whatever reason you are convinced you must have zoning I say trying to throttle down a system large enough to whole building, in an attempt to make one zone happy does not seem likely. Most zoning systems have a dump zone where the system sends its excess capacity without regard to what happens to the temp in that room.

    I think having several smaller independent systems is a better solution than one large zoned system.


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