Help with mini split decision please

6 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
6 years ago
last modified: 6 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
6 years ago
last modified: 6 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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Beautiful home! Here's the straight poop on mini-splits and contracting air conditioning in general. Mitsubishi, Fujitsu, LG, Sanyo, Toshiba, and most other brands are all pretty much alike, technology wise. I have installed a lot of Fujitsu and have friends that have installed other brands. When we compare notes, they all seem pretty much the same. They are most all Japanese and use the same technology. By the way, ductless split systems are the absolute best option in my opinion. They offer reliability, extreme energy efficiency, and flexibility. All contractors are NOT created equal. Here's where the big difference comes in. Most homeowners, when deciding on a new system get three "bids". Getting different options is a great idea. Getting three "prices" is almost always a bad idea. When you shop based on price (not that you are), contractors know this and will adjust their pricing accordingly. IF the scope of work and the quality stayed at a high level this would be great. The fact is that if a contractor knows he is competing based on the cost of the job, he will cut his cost in order to compete. This almost always means cutting quality and things that contribute to the reliability and energy efficiency of the system. A good strategy is to get three contractors to give you their recommendations based on what you would like to accomplish. Ask for a list of past customers you can call as references. A good contractor will be anxious for you to talk to his past customers. A poor one, not so much. Make your final decision based on all the factors you have, but give extra weight to how you feel about the quality of the contractor you are considering. You will have to live with this decision for a long time. Make it a good one. Ductless split systems are, in my opinion, the future of HVAC in this country and are already more common than conventional systems in other countries. SEER ratings are based on average heavy loads. Since your heating and air conditioning system rarely operates at these kinds of loads, the SEER isn't a good reflection of what you can expect with ductless split systems. These systems have much better control than conventional systems and are able to increase or decrease the capacity of the system based on the load on the system. I have written several articles on the ductless systems and current debates. Please feel free to see one of them on my blog, here. Good luck on your new system. I know you will be happy with ductless technology.
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@fsq4cw - how about a ballpark price just for the air-to-water heat pump? Just out of my own curiosity. Note that due to @mtvhike having a fairly large solar array and the specifics of his tariff scheme, I'm not sure that any significant capital cost to reduce his electricity usage will pay off well. This shows one of the oddities about specifics of solar tariffs. As I understand the way it works is this: his base tariff for electricity is 9.5 cents/kwh. Any solar he generates offsets the electricity he consumes (calculated annually?). BUT: any solar generated in excess of consumption is only paid at the wholesale rate, which is dramatically lower than the retail rate (call it 1 cent / kwh). Right now - without full year data - he expects to consume somewhat more than his panels generate. The upshot is that his savings from reduced consumption are limited (You could analyse this differently but I find it easier to just take what he already has as the base case, I think the conclusions are the same). Let's say, for example, he consumes 4,000 kwh annually more than he generates, for a bit less than $400 (netted out annually). If he saves more energy than that, every 'extra' kwh saved only gets him 1c / kwh. At least unless or until he adds some significant extra load, like buying an EV or putting an aluminium smelter in his garage or something. So: I'd say it makes sense to consider a minisplit primarily for the air conditioning comfort and if it also offsets some of his straight resistance heating, great, there's some modest savings there (within a 'limit' of however much his consumption currently exceeds his solar generation). Spending much additional for the 1c/kwh savings just won't make much sense financially. This is pretty simplistic as right now he has historical data for consumption and the solar array is relatively new so annual generation only estimated, and of course from year to year both may vary. And at any rate, a good argument to not rush into anything with high upfront expenses or to prioritise other projects for the time being.
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sktn77a
6 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.

Help with mini split decision please

Comments (3)

hvac guy

David Cary

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