Help with mini split decision please

8 years ago

We have gotten 3 rather different quotes for a mini split heat pump. We are trying to figure out which is for the correct equipment, or whether we need to ask for something else.

About the house. It is a townhouse (not an end unit), built in 1974. The house is located in Deep Creek Lake Maryland and is Lakefront. It is a 1440 square foot split level with a total of four levels, 3 bdr, 2 ba with a very open floor plan. 3 of the levels are very open. When you walk in on the first level you enter the kitchen/dining area. If you go downstairs there is a small hallway with the master bedroom, another bedroom and a bathroom. The master bedroom is 16.5 feet x 9.5 feet. There is also a walk in closet and a utility closet w/ a washer/dryer that are off of the master bedroom, but not included in the square footage of the room totals. We are looking to put a head in this bedroom. This level is on a slab, and there is a 78” sliding door out to the lake. That is the only door/window in this bedroom.

The other bedroom on this level is 10 x 9 feet.

The kitchen dining level is approx. 21 x 12 feet. If you go up from this level you are in the living room. This is one large room that is approx. 21 x 22 feet with very high cathedral wood ceilings. The back wall of the room is all windows and sliding doors. It is a north/east exposure. We would put a head in this open living room/loft area.

Up the stairs from this level is a loft that is open to the living room and then a small bedroom which is 9.5 x 9.5, and a small bathroom. We would like to put a head in the small bedroom.

The house currently has baseboard heat and one ceiling fan in the living room.

The quotes we have received are for the following:

1) 48,000 BTU Mitsubishi Hyper Heat – outside, with 9,000 BTU units in upstairs bedroom and downstairs bedroom. 24,000 BTU unit in living room/loft area.

2) 36,000 BTU Mitsubishi (not hyper heat) – outside, with 6,000 BTU unit in upstairs bedroom, 12,000 BTU unit in downstairs bedroom and 24,000 BTU unit in living room/loft area.

3) 30,000 BTU Mitsubishi Hyper Heat – outside, with 6,000 BTU unit in upstairs bedroom, 12,000 BTU unit in downstairs bedroom and 18,000 BTU unit in living room/loft area.

4) 36,000 BTU Fujitsu – outside, with 7,000 BTU units in upstairs and downstairs bedrooms. 24,000 BTU unit in living room/loft area.

The main purpose of this is air conditioning and dehumidification. I hate to be hot! Heating is a nice bonus, because it is more efficient then the baseboard heaters currently there. All of the proposals are in the same expensive ball park (about 11K range)!

Anyway, my thoughts are #1 is overkill. #2 would be ok with a smaller unit in the master bedroom? How small 6,000 or 9,000? #3 - the contractor said that with dropping down to 18 from 24 the room may take longer to cool down when we first arrive for a weekend. #4, by default seems like it may be ok?

Any and all thoughts are appreciated. Do we need hyper heat? Should we consider other brands that may be less expensive like LG or Trane.

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Comments (3)

hvac guy
8 years ago
last modified: 8 years ago
I won't be much help as I'm strictly a service tech on the commercial side of the industry but, a heat load calculation should be done in each zone (if not already done) to give you guys the best match in terms of unit sizing.

Another thing to take into consideration is the fact that they'll have to run a lineset and wiring to each individual air handler from the condenser and depending on the layout of the structure, that could be a factor in the pricing. Between the different brands, I'm not sure how much pricing difference there is, assuming all are the same efficiency rating.

Most of the mini splits I've worked on have been the Mitsubishi brand, some for comfort cooling and most for small IT closets. I've never worked on LG or Trane mini splits, but service, manufacture support, and parts availability for the Mitsubishi units have been great for me personally. Hopefully some of the other guys more familiar with these can help you out more.
David Cary
8 years ago
last modified: 8 years ago
Do you have an a/c already? If you haven't learned already, nearly every contractor does a sloppy job with load calculations and oversizes everything.

Nearly the only thing that matter is western windows. Eastern windows create heat gain but in the morning when ambient temps are lower. Southern windows don't usually get a lot of solar gain but that depends on overhangs. Northern - zero solar gain.

In a small house the number of occupants matters as does cooking and showers. The loads seem as expected - high. I would do the smallest units on each floor that you can - 6,000? except the highest floor which should get 9,000. The lowest floor probably does not need 6,000 but you probably can't get lower. But all that is WAG.

1st arrive for the weekend? That is what wi-fi controls are for, not oversizing.
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sktn77a
8 years ago
I'm guessing a 30,000 btu system would be more than adequate for your home. Oversizing will result in poor dehumidification. As far as individual rooms, you need a heat gain/loss figure for each of those rooms in order to size the equipment. Judging by the range of capacities, I suspect no-one did an appropriate sizing estimation. Before you make a decision, insist on knowing how they came up with their sizings and anyone who can't justify their recommendation should be removed from your list ("I've been doing this for 30 years......." is not a justification).

And remember, heat pumps (minisplit or other) are sized based on cooling needs, with supplemental heat for any excess heating needs.