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View Full Version : Anyone have real world experience with mini-split air conditioning?



Brian Elfert
01-11-2014, 8:40 PM
I'm looking at buying a home that has no central air conditioning. The home is 1,900 square feet and strangely enough has two boilers. Does anyone have real world experience with mini-split air conditioning?

I hate window airs due to cost of operation, noise, and just dealing with them sticking out of windows. There is no way to add forced air to the house so mini-splits are the only reasonable option I know of. Are they more or less expensive to run than traditional central air conditioning? I have such a sensitivity to hot humid air that I would never own a house without air conditioning. I expect the cost of mini-splits would probably be as much or more than the cost of adding contral air to a house that just has a forced air furnace.

Ethan Melad
01-12-2014, 8:50 AM
Brian,

We built our house with 3 mini-split units and they're great. Will you be using them for heating or just cooling? I think virtually all mini-split units are more efficient and cheaper to run than traditional central air. I actually have never lived in a place with central air, and don't particularly mind hot weather, but when we use the A/C it works very well. Our units also have a dehumidifier built in. I could be wrong, but I'm pretty sure that overall cost would not exceed adding central air since theres no ducting needed. We also use ours for heating as a backup to the wood stove, and it does a good job there too.

Brian Elfert
01-12-2014, 9:29 AM
My primary use for mini-splits would be air conditioning, but I might do heat pumps to do heating during the milder parts of the heating season.

Chris Damm
01-12-2014, 9:40 AM
I have HW heat so I was stuck with window AC. We put in replacement windows and the only window units that would fit were 5000btu. Not big enough and noisy. We had a Daikin mini-split installed about 5 years ago and have been very pleased with it. It is a heat pump so you can use it for heat too. We had to shut our boiler down for a couple of days during a kitchen remodel and it kept the house comfortable in 10 weather.

Matt Meiser
01-12-2014, 11:24 AM
My parents put one in about 14 months ago. Theirs is a 6 headed Mitsubishi Mr. Slim. Overall it was a good choice for their 1860's farm house, but their contractor was downright awful. It took half of last summer to get the system fully operational--some units wouldn't work right, some at all, the whole system shut down once on an error and one room flooded multiple times due to bad condensate drainage (you'd think a company that also does plumbing would know water can't flow uphill.) The units aren't exactly pretty but they aren't too bad. They have 5 of the typical wall mount units mounted up high in various rooms plus one "floor standing" unit which is a misnomer since it actually attaches to the wall down low. There's a ceiling mount unit too but they don't have any of those.

I don't know how their bills were but I didn't hear any complaints about it which is a good sign. I think we are finally getting my mom to understand that it is not a savings to close off a room and turn off that unit for half a day, then open it back up and crank the setpoint on unit as low as it will go to "get it cool faster."

The only other gotcha, should you decide to install a standby generator like they have, there's no 24V control wire to interrupt like a "normal" AC system for load-shedding. They had to buy a contactor which the electrician was able to actually install inside the outdoor unit for a neat install.

Brian Elfert
01-12-2014, 11:47 AM
One condenser with multiple evaporators sounds ideal, but I wonder how much it adds in labor to have to snake refrigerant lines all over? I also didn't think about how to deal with the condensate. The house is a little unusual, at least for Minnesota, in that it has a slab for a good part of the house and then a small basement under a 15 year old addition. One can generally add central air to an existing forced air system for maybe $5,000. I bet it will cost as much or more for mini-split installed. I'm thinking about asking seller to install mini-splits instead of offering a reduced price.

I have a standby generator on my house today and I have the central air wired to it. I don't do anything to interrupt the central air, but I also don't have whole house wired to the generator.

David Weaver
01-12-2014, 12:01 PM
This will probably sound quacky, but I'd rather have two splits, one on each end of the house. The small units are more efficient than the big units and you won't ever be in a situation where both are down.

If you have 1900 sf, 30k btu will probably be enough to cool the area, and the 9-18k btu units are all in the 20 seer/14 eer range.

We have an old 24k btu central unit in the house, and a 15k split in an add-on room. With the door open, the split will cool the add on room and most of the rest of the living area of the house, leaving us to only turn on the large unit now for bed, and our bill has gone down. I'd add heat, it doesn't add much cost and the heat is probably even-up cost or so compared to gas heat when the temp is 30 degrees or above - plus you can zone it more easily.

It cost me about $3200 installed for a 15k mitsu unit, but I went through my contractor to do it. The local HVAC place that's mitsu certified wanted to hang me to the wall and charge over $4k for a 9k btu unit from the same line as the 15k is in, and then sell a bunch of proprietary plastic line-hiding garbage for another several hundred bucks (I hid my line set with wood trim instead

Brian Elfert
01-12-2014, 12:31 PM
I don't have an issue with two units and my original thinking was that I would need multiple units. The house has a kitchen, informal dining room, a family room, and two bedrooms with a bath on the main floor. The second floor is a huge master bedroom loft with an enormous bathroom. The family room is open all the way to the second story ceiling. One of my concerns is that the house would have even cooling like central air.

The only reason I am even considering this house is because of the lot. It is 2.75 acres very close to the city. Most homes in the same area have 1/4 acre or less. One issue with the lot is the city is very restrictive on what type of accessory structures can be built. The city is used to dealing with tiny 1/4 acre lots common to the area. A building big enough to house my 43 foot converted bus would not look out of place on a 2.75 acre lot, but city rules only allow a 14 foot tall building which is not tall enough for my bus by the time you add roof pitch.

I would prefer to build new, but it means commuting 2 hours a day probably to get to a place that would have enough acreage to build a building for my bus. This house I am looking at is a lot older that I would like to buy. It really needs new windows on the 1950s part of the house and a new kitchen.

Malcolm Schweizer
01-12-2014, 12:40 PM
I live in the tropics. Electricity being at a premium ($0.55/KwH), A/C is rare. Most of the year it is 82F but in the summer it gets into the 90's. Most people here use window units in the bedroom at night and the rest is cooled by simply opening the windows. (Less wind at night so it feels hotter.) A lot of people, however, use split units. Our homes are concrete and attics are rare, so there are few places to run duct work. Also our houses are usually very open floor plans, so split units work well. I would say 90 percent of the A/C here, not counting window units, is split units and only 10 percent central A/C.

A split unit will be similar operating cost for same size central unit. The difference is you get all the cold air in one place as opposed to ducts directing air to each room. Also installation is a lot cheaper and easier. For open floor plans they work great and are easy to install. You can run two small units off one compressor and spread out the cooling. You do have the disadvantage of the condenser/blower unit being somewhat obtrusive. Still, it looks better than a window unit.

For me a home at 80F is comfortable. That's the temp now and I am in long pants and long sleeves and comfy. Last night it got down to 75F and I had blankets on the bed and slept in pajamas. Acclimation is a big part of comfort. We are buying a house with a very rare central unit upstairs and two split units running off one compressor downstairs. One is in the master and the other in my shop. (That's just where they were installed by the original owner.) I plan to never use the central A/C except when guests visit that are not acclimated to the heat, and will use the split units during the summer if it gets really hot. Admittedly, I do like the idea of having A/C in the shop, which I have never had before. I hope I don't get spoiled.

Brian Elfert
01-12-2014, 5:17 PM
I work in an air conditioned office and have an air conditioned home so I am not outside enough to really get acclimated to the heat in the summer. I had heat exhaustion twice in three weeks in 2003 and now I get sick easily when exposed to too much hot humid air. I work a lot on my bus conversion in the summer and always run the A/C when working inside it. Productivity is much higher in cool dry air.

Electricity is comparatively cheap here (11 cents a KWH) so most everyone has air conditioning. They couldn't sell a new house here without central air. A/C is only needed two to three months a year, but it can get downright tropical at times.

Jim Matthews
01-12-2014, 7:53 PM
I bought a hydraulic lift on wheels, 12,000 BTU in window unit, mounting shelf and dedicated 220 line for less than 1/3 the price of a similar sized mini-split.

I would spend money on passive cooling, first.
My next expenditure will be awnings for our windows that face South and UV filtering films.

Brian Elfert
01-12-2014, 10:32 PM
I understand that window air units are less expensive, but I really don't want to deal with the hassle, the noise, and the extra cost in electricity. I may have to anyhow if the mini-splits are too expensive.

David Weaver
01-12-2014, 10:56 PM
I had the opportunity to either put a slide-in unit (heat pump A/C combination) or the split. The biggest difference between the slide in and the split for me (and something that doesn't help brian) is that the split handles true cold so much better. My unit is very effective all the way down to 0 degrees, and it will run to -13F. Personally, I shut it off when it gets below 10 degrees because I don't want to pay for it to run a coil to assist the heat pump.

At 30 degrees, it only uses a whiff of electricity, and the A/C is the same way - it hasn't gotten hot enough here for it to move the meter much.

The slide in EER was 9.5 or 9.0, depending on which one I bought, and I don't know what the SEER was - 13 or something, it was a different technology than the splits (that use an inverter and runs the compressor variable speed depending on demand). My MIL has to be able to sleep in my addition during the winter, thus the extra spending. The slide in only worked down to about 15 degrees, which is something we see regularly at night. If MIL was out in that room and the heat pump shut off when it's zero degrees, I"d be in trouble.

I could tolerate the slide-in otherwise, I was just afraid my wife would be running it in the winter close to where it shuts off and it would be using max electricity - and that has nothing to do with A/C.

One other consideration, it requires 220 (mine does) even though the draw is not very high. Full out without the coil, 15k btu takes less than 1kw. But the 220 line is required, and a standard whip/disconnect setup is required and that was about $275 of the cost of mine.

One other benefit of the splits (mitsus, at least). If you put them on smart-fan, you won't hear them running inside or outside. They are essentially noiseless.

Jeff Erbele
01-13-2014, 1:05 AM
I don't have an issue with two units and my original thinking was that I would need multiple units. The house has a kitchen, informal dining room, a family room, and two bedrooms with a bath on the main floor. The second floor is a huge master bedroom loft with an enormous bathroom. The family room is open all the way to the second story ceiling. One of my concerns is that the house would have even cooling like central air.

The only reason I am even considering this house is because of the lot. It is 2.75 acres very close to the city. Most homes in the same area have 1/4 acre or less. One issue with the lot is the city is very restrictive on what type of accessory structures can be built. The city is used to dealing with tiny 1/4 acre lots common to the area. A building big enough to house my 43 foot converted bus would not look out of place on a 2.75 acre lot, but city rules only allow a 14 foot tall building which is not tall enough for my bus by the time you add roof pitch.

I would prefer to build new, but it means commuting 2 hours a day probably to get to a place that would have enough acreage to build a building for my bus. This house I am looking at is a lot older that I would like to buy. It really needs new windows on the 1950s part of the house and a new kitchen.

This doesn't make sense; the lot and location are desirable but the house is not what you really want, but most of all building codes will not allow a a building tall enough to house your conversion bus which is your objective.
Plus earlier in another post you wrote the bus was going to be for camping and here you state you even run the bus AC when working on it, because you cannot tolerate the heat and humidity; which makes me wonder why your goal is to spend time in the great outdoors. It sounds like get the most fun out of the bus-camper project; camping after it is done, I don't know.

On a potential bus garage, not knowing the lot, terrain and drainage, would it be possible to extend the total building height by having part of the building in the ground with the lower part being concrete?

You would not want to dig down and have runoff fill your building. It would only work if it drain away from the building.
Another thought is to have the gable open too. It would take some creative designing but could work. A lot depends on which type of structure you select.

Brian Elfert
01-13-2014, 8:40 AM
This doesn't make sense; the lot and location are desirable but the house is not what you really want, but most of all building codes will not allow a a building tall enough to house your conversion bus which is your objective.
Plus earlier in another post you wrote the bus was going to be for camping and here you state you even run the bus AC when working on it, because you cannot tolerate the heat and humidity; which makes me wonder why your goal is to spend time in the great outdoors. It sounds like get the most fun out of the bus-camper project; camping after it is done, I don't know.


I do spend plenty of time outdoors. I just don't want a house without air conditioning. My bus conversion is used mostly for trips out west where the weather is more tolerable.

I'm going to talk to the city, hopefully tomorrow, about the possibility of a variance that would allow a taller building. If they say there is no possibility then this house is out of contention. My bus is 12' 9" tall. It really requires a 14 foot door. A pitched roof is required so the peak of the roof can only be 14 feet.

Mike Hollingsworth
01-13-2014, 10:21 AM
Make sure condensation lines are installed correctly. A/C installers don't have to pass high school.

Jeff Erbele
01-16-2014, 12:43 AM
I do spend plenty of time outdoors. I just don't want a house without air conditioning. My bus conversion is used mostly for trips out west where the weather is more tolerable.

I'm going to talk to the city, hopefully tomorrow, about the possibility of a variance that would allow a taller building. If they say there is no possibility then this house is out of contention. My bus is 12' 9" tall. It really requires a 14 foot door. A pitched roof is required so the peak of the roof can only be 14 feet.

Thanks for clarifying. A variance is a great idea, so you can get what you really want. The justification being it is a larger lot and can accommodate a larger building with out appearing crowded or out of place. I would get it writing so you don't get stuck buying the property, then being told, "we never said that".

Brian Elfert
01-16-2014, 9:54 AM
Thanks for clarifying. A variance is a great idea, so you can get what you really want. The justification being it is a larger lot and can accommodate a larger building with out appearing crowded or out of place. I would get it writing so you don't get stuck buying the property, then being told, "we never said that".

Nobody at the city can assure me of getting a variance. The city planner can only say if they think the variance would be approved by the planning commission. The city planner can also say if city staff would support the variance or not. If city staff doesn't recommend approval of a variance it would be hard to get planning commission approval. The planning commission has final say and I can't actually ask for a variance if I don't own the house and also have concrete plans for what I want to do.

I'm having trouble talking to any of the city planners at the city. I left a message for one on Monday and no call back. She works Monday to Wednesday and the other planner is on vacation. I left another message today. It wouldn't be the end of the world if the planner told me she thought the variance would be approved and it did not get approved later. It is still a nice lot that leaves me plenty of room to park my converted bus. A lot of city lots have no room for a 43 foot bus.