Mini-splits throughout the house?

jagoe1January 12, 2014

Hi there. Has anyone put in mini-splits throughout their home for air-conditioning? We originally planned mini-splits in the basement, along with high velocity for the first and second floors in our 1895 D.C. rowhouse (approx. 2,500 sq ft total) in an attempt to eliminate bulkheads and preserve some of the tin ceilings. And we are keeping the radiators.

Our contractor then suggested that we switch to a mini-split unit system for the top two floors - essentially putting mostly ceiling cassettes or compact cassettes - in each room. (We do not want wall units in the upper floors.) Has anyone gone this route? Would live to hear your thoughts, good or bad. Thank you!

* Here's what the original (high velocity) plan called for:

Space-pak high-velocity system for first and second floors. Manual J-load calc to be done for HVAC system. There shall be at least one return air grate and digital programmable thermostat on each floor -- i.e., the first and second floors shall operate as independent zones. He priced the installed system at $16,000 in the contract.

* Here's what the contractor is now proposing:

Manual J-load calc
Cassettes or compact cassettes

The first floor would likely be ceiling cassettes for the dining room and kitchen, and a slim duct installed in the wall for the living room, where the ceiling is tin and access is limited. Second floor would all likely be ceiling installation, with the coolant lines running through the attic.

The units would be sized to the individual rooms. (He hasn't yet said how many he plans to use.) Wall-mounted options range from 7k - 24k BTU; compact cassettes from 9k - 18k; slim duct 9k - 24k. The mechanical guarantee is 7 years on the outdoor units; 2-5 years on the indoor ones depending on which ones.

Contractor says mini-splits are way more efficient, up to 27 SEER, and allow control by individual room. He says two downsides used to be cost and appearance of the wall-mounted units, but notes prices have come down and that the cassette provides an alternative to the outside-of-the-wall installation.

We are leaning against mini-splits for the upper floors, mainly because the concept is so unfamiliar to us - also, we're not sure how attractive these cassettes will look. But we wanted to make sure we weren't dismissing a good alternative.

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I have a high-wall Mitsubishi in each of 7 rooms in my home for cooling and heating. I am starting my 4th year of operation. There have been a lot of developmentts since then. The only place that I don't like the look is in my dining room which is the smallest room.

They work well. SEER is only part of the efficiency story. No ducts losses is important. Ducts leak. This is not a huge problem unless the ducts are outside of the home envelope(Attic). Leaking supply ducts in the attic blow conditioned air out and that results in make-up air being sucked in elsewhere, randomly. Leaking returns suck air in and pressurize the house. You've also got the pressurization/depressurization of individual rooms to consider unless you have a return in each room, large undercuts on the doors or jump ducts.

Downsides have to include no inherent ability to install central humidification (not in your case since you will heat with radiators) or dehumidification. I'd prefer to have a wall-mounted thermostat, but that was not available at the time. Now it is. I can not do true set-backs with my system which would be nice in heating season. Fortunately for me with my system, we don't have much of a heating season were I live.

I just looked at Fujitsu's web site and I don't see anything below 9000 btu. I have some 6000 btu and when mine were put in, there were 5000 btu units available, IIRC. That was one reason to stay away from ceiling cassettes, too big for my dinning room. Has your contractor considered some of the small, minimally-ducted mini-splits? They can handle more than one room. You might have some place inside your home's envelope that you can hide some. You could consider enclosing them in the attic to to put them inside your envelope.

You probably have small rooms. Even though they can run at lower capacity, you want to be as close as practical to your capacity.

That takes me to a subtle element in a system design detail that might escape many people. The outdoor units can only throttle to a certain percentage of their max capacity. That means that they must begin to snap off and on at some low-load point. That would typically be at night in bedrooms. That means that if you have more than one outdoor unit, you probably want the smaller one running the bedrooms.

Note that all of my wires and pipes are inside of my walls. There are no holes all the way through my outside wall assemblies. All but one of my indoor, high-wall units are in inside walls. My home, however, is a 1930ish, raised home over a crawlspace. Plaster had to be cut for access in one spot where two installations were done. Other areas (3) needed to be modified, but there, gas and electric wall heaters were removed. You might be able to run your condensate lines to your basement, but future access should be considered in case of condensate drainage problems.

I've posted a lot about my mini splits and I am a chauvinist. See if you can find my posts with a search. I'll be glad to answer any specific questions. Maybe your contractors's distributor has "gutless" mock-up of the high-wall units that you can hold up in different places in your rooms. If not, consider making yourself a box of a similar size if that will help you visualize it.

    Bookmark   January 13, 2014 at 12:36PM
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duplicate post deleted

This post was edited by ionized on Mon, Jan 13, 14 at 14:01

    Bookmark   January 13, 2014 at 12:49PM
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You say you will use these for cooling as you have the radiators, but I think you will find that you end up running your boiler only when it get really cold. Heating performance on these mshp's is outstanding. I heat and cool my home with Fujitsu's and Rinnai Energysavers. I pulled the entire central system, not because of poor equipment but because of very poor ductwork.

I was the rep for Fujitsu for 12 yrs prior to selling my business and moving west. They make great equipment. It is difficult to advise without a floor plan, but as I see it, you have a few choices. You could go with a multi 2, 3, 4 or up to 8 evaporators on one outdoor condensing unit. Those tonnages can go 1.5, 2, 3, or 4 and the interior unit combinations and evaporator styles can mix and match. One thing I will say about the cassettes. Make sure you have service access. I concur with Ionize on the mini-ducted unit. they can work out very well in the transoms over closet doors and in attic areas. I hands down prefer the wall unit and find that they, just like everything else in the house blend in over time. The longer you live with them the better looking they become. You choice, but I think they are the best. I actually did a daily extensive, but informal, study on this. many times if I was involved at the beginning of the job and was told, "none of those ugly high wall units", when, for one rason or another they were installed I would go back after a while to see how they were. The comments were universally positive. Grudgingly so, at times, but people were happy with them.

Mini splits are tremendous for dehumidification. I installed a dual system upstairs. I went with singles downstairs. These represent the ultimate in zone control, so we rarely run the upstairs units a lot. Downstairs I run a 25 seer 12RLS and I think it is a 21 seer 15RLS. That to me is the right combination. Very highest efficiency units in the primary living area and combis in the less used areas.

Do not have a unit blowing right down on top of the bed. The cassettes can be 2, 3 or 4 way blows so that is adjustable. i'd suggest that you look at Go to the Contractors tab and there you can download the entire catalog and they are very good about publishing specs.

As to the hi-velocity units. They work. They are installation sensitive in the ducting and they are much less efficient. When the 13 seer mandate went into effect the hi-v folks used an exclusion (confined space) to not have to meet it. In my experience they cannot compare to mini-splits for either comfort or efficiency.

As with so many things mechanical, hire the best guy you can find and pay him what he is asking. Having made a lot of site visits on problem installs I can tell you that there is no substitute for "do it right the first time" on these.

    Bookmark   January 14, 2014 at 9:53AM
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OP, what is your climate (location)?

Jackfre, if the OP has an efficient natural gas boiler, heat will cost less than with a mini-split right now. Of course we all want a crystal ball that will predict the future :-)

I have a question for you jackfre. The OP might want to know too so I'll risk hijacking the thread. What are the advantages of going with one large minisplit outdoor unit vs. two or three smaller ones? Is cost lower for the equipment? If so, is some of that sometimes advantage lost due to higher cost of installing refrigerant lines because some indoor units are located further from the compressors?

One advantage that I see to smaller and dual or multiple is that in low demand mode, or when you are running few or a single indoor unit, the smaller compressors will be running more constantly at a lower capacity than the big one can. For example, if a compressor on an 18,000 btu compressor can run at 20% of max capacity, that will run a 6,000 btu indoor unit at 3,600 btu. If that same indoor unit is coupled to a 30,000 btu compressor, it can only run at a minimum of 6,000 btu. On the other hand, if you go to the extreme and have all 1:1 systems installed, you can run your 6,000 btu indoor unit at 1,200 btu given the 20% figure. Please correct me if I am misguided about this.

A couple of other advantages are that in case of failure, you can still heat or cool some of the home and the smaller units can be run with a relatively small fixed or portable generator.

    Bookmark   January 14, 2014 at 10:53AM
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If you can, try going to Open Houses in your neighborhood to see how others have dealt with HVAC challenges while preserving the charm of their old houses.

Personally, I'd be more concerned with appearance and less concerned with efficiency. And on that score, I think the various in-room options for mini-splits look hideous. If you find other homeowners in DC have gone in this direction, fine. If not, I'd suggest that appearance will play a larger role in your home's ultimate sale than any claims of A/C efficiency. You don't want to own the most efficient house on the block that no one wants to buy.

    Bookmark   January 14, 2014 at 12:14PM
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Ionize, with any modulating equipment the most important thing is not how high it will go, but as you point out, how low will it go. I was selling modulating gas equipment in '91 before anyone else was on the market with it and people thought it was magic. And it was, and is! Your real comfort is determined by how low it will go. My 12 and 15 kbtu Fujitsu's go down to around 3,600 but. My Dual 12's will individually go down to around 5500 I think it is. Seer on those units is 25, 21 and 16.5 respectively

As to the cost of the system vs the equipment spec'd, I think the lay-out makes the call. The contractor has to be able to lay it out based upon need, options, value etc. You just cannot make a hard and fast statement. Limiting factors like Elec panel capacity, line-set lengths and to me one of the very most important issues in the decision is, how do you live in the house. I don't mind having the less efficient multi upstairs because I haven't run them at all since probably Sept. Heat rises and the upstairs is perfectly comfortable and I want it a bit cooler. It is available if I need it. In the summer I run that one when it is really hot, but most nights I run it on fan only with the windows open. No humidity here in CA. Sadly, no water this year either. The Sierra are a 16% of where they should be at this point and last year was the driest on record.

Interestingly, I was talking with a contractor up in N CA some time back and he had done two homes that were virtually identical. He did one conventional hi- eft propane and AC. The other he did the 4ton outdoor with 8 indoor unit Fujitsu. I asked how it come out. He said surprisingly the installed cost on both systems was very near the same (keep in mind this was new construction) and both were operating well. He did go on to offer that the mini-split system was operating at about 45% of the cost of the conventional ducted system.

You took a big step doing this a couple years ago. Good call, imho! Oh, but Snidely won't buy your comfortable and efficient house!

    Bookmark   January 15, 2014 at 12:32PM
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"Snidely won't buy your comfortable and efficient house!"

No I wouldn't, and I suspect neither would many others. Want to take the chance?

Let's look at what you find on the market, pick your area as a for instance. Even in places like the Sierra foothills where natural gas may not be available, and even as much as some people dislike propane. Why are these mini-splits so rarely encountered?

What you are finding more and more (in upscale properties) is ground source heat pumps. It's ducted forced air all the same, it's what most people want.

    Bookmark   January 15, 2014 at 3:38PM
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Having travelled over most of the world while in the Military, I find it interesting how we as Americans are so Reluctant to adopt technology that will obviously save us money, and is a no brainer for the environment. Maybe some folks don't understand what SEER equates to but bottom line is directly correlates to your Electric Bill. Sad but true having spent the last 10 years in Refrigeration I have unfortunately crawled down many of these low pitched roof attics here in Florida, The Heat in that attic with the best Attic fans running is still well over 100 degree's. The cabinet on many of the AHU's are not designed for this kind of Heat infiltration. I moved on to working 95 percent Industrial Refrigeration but still wouldn't have anything other than a nicely hung Wall unit through out the rooms of my Home. Bottom line in my case was over 300 dollar electric bills during the Heat of the summer. Now 180 dollar Electric Bills. I imagine with some upgrading to my Water Heater (solar) I can knock it down even further. The rest of the world Asia, Europe use these High Efficiency units exclusively because their Energy costs are much higher than ours, but bottom line is it is the right thing to do for our Planet.

    Bookmark   July 12, 2014 at 5:47AM
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not everyone is reluctant, but those of us who
recommend these units often encounter resistance
from hvac companies, and hvac supply houses.

educating the masses is one thing...
educating pro's is another.

great thread, thanks Ionized & Jackfre.
(and howdy Snidley!)

I'll have to bookmark this thread for minisplit info.

best of luck.

    Bookmark   July 12, 2014 at 1:44PM
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