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The versatility of mini-splts

richardi's picture

I am having a house built in which I planned to heat primarily with RFH using mini-splits to supplement the heat when needed as well as providing A/C.

The GC contacted his HVAC gyb who suggested that I didn't need mini-splits for the lower level ( a walk-out basement), instead recommeded a whole house dehumidifier.

From what I've read, mini-splits can dehumidify in addition to the cooling and heating capabilities.

I'm thinking a larger capacity condensor (Fujitsu AOU48RLXFZ) and a couple of additional indoor units for the lower level would be more cost-effective than a dehumidfier. And provide much more 'conditioning' flexibility?


why a "couple of indoor (post #207324, reply #1 of 25)

why a "couple of indoor units"?  is the basement partitioned?

dehumidifiers are fairly inefficient.  if you only need to dehumidify during the cooling season, the minisplits are better.  but if you need to dehumidify year round, you can't do that with minisplits.


Rockport Mechanical

HVAC Design and Installation in beautiful Rockport Maine

dehumidifaction (post #207324, reply #2 of 25)

Yes, the basement is partitoned; a wine cellar, a home office, a bedroom and a 'yet to be determined' room. And, yes, I'm thinking dehumidify primarily during the cooling season. If the radiant heat works (discussed in another post) then there should be no need for a dehumidifier during the heating season. If it doesn't...

Reconsider: YOU Decide (post #207324, reply #3 of 25)

A couple of pointers:

1) It's a lot cheaper to have, say, two separate 1-ton mini-splits than to get a single 2-ton unit with multiple heads.

2) Multiple mini-splits quickly add up to a much higher 'installed' cost, than a whole-house air conditioner- even if you need to replace the furnace.

3) The advantage to multiple mini-splits is that you can easily control different areas independently. This means that, for example, you'll be adding air conditioning only in the room the sun is heating at that moment- rather than cooling the entire house.

4) As you suspect, the ability of any 'heat pump' to heat your house is quite limited.

5) You're correct in suspecting that basements have their own conditioning needs. I'd like to speak on that for a moment.

Why do basements have humidity issues? Well, I attribute it to two reasons:  basements are cooler, and basements are not ventilated as the house is.

As such, basement air flow has to be independent of the house above. Usually, folks draw from the house to heat and cool the basement; IMO, this is exactly backwards. What's going to happen when warm, moist air hit the cooler basement walls?

No, you're better off massively increasing the supply of fresh air to the basement, and conditioning that air independent of whatever is happening in the rest of the house.

The way you build walls and floors in the basement ought to be different from the way it's done upstairs as well. Again, draining off condensation is an important design concern.

Trying to decide (post #207324, reply #4 of 25)

Have you seen the the Fujitsu AOU48RLXFZ compressor? On paper it sounds like my 'solution'; up to 8 zones. The indoor units could be used for supplemental heating, air conditioning and dehumidification. The latter in leiu of a (inefficient) wholew house dehumidifier. By the way, the basement walls will be insulated at some point.

+1 (post #207324, reply #5 of 25)

Good comments on basement HVAC. 

The simplest way to approach what is needed for any conditioned space is to have the load calculations done.  That sounds simple, but most builders and home owners don't do it.

The load calculations should be for both heating and cooling loads, and as you pointed out, for each floor, including basements of the house.  There are modeling programs available that are pretty darn good at predicting usage.  By varying the combinations of insulation, wall structure, windows and doors one can get a virtual look at which combination works the best for a particular home design and local.

I had that done when in the design stage of my home.  It was a driver in both the construction framing, insulation selection, and HVAC system design. Your comment on zoning was proven out in my case, but had a little twist to it.  I too have a day light or walk out basement, Fully finished.   The surprizing twist was that my heating/cooling loads actually shift from one floor to the other durring the heatin and cooling seasons.  For that reason I have seperate ducting and zones for both the first floor and basement.

It it not to late for the op to have those load clacs. done.  A good HVAC contractor or energy engineer can do the modeling and design  and take the quess work and questions out of the equation.  He will need to pay for that service, but long term it is a far better investment than letting some builder or HVAC contractor just shoot from the hip, because" that's the way they have always done it."

Amen x 3 (post #207324, reply #6 of 25)

Amen x 3

I know you have already (post #207324, reply #7 of 25)

I know you have already decided to go with mini-split systems and they are definitely a very efficient way to heat/cool some homes but to me they are just way too ugly.  I can see a use for them in a converted attic where you need additional cooling/heating that wasn't designed in but I just can't see living in what looks like a hotel room.  To me its like marrying an ugly woman because she can cook and chop wood.

Not trying to change your mind or suggesting you do so.  Its just my personal opinion.  I would have to find some way to hide the thing inside a wall or closet somehow if it were possible.

Don't need to be ugly (post #207324, reply #8 of 25)

I appreciate your response and I agree with everything you say, even the ugly woman part. However, there are options besides the standard wall mounted units. Compact cassettes (22.5" x 22.5") fit into a ceiling and can provide 9K, 12K or 18K BTUs. Slim duct units can be hidden almost anywhere there's as little as 9.5" clearance. The only visible parts are the supply and return registers. The can provide 8K, 12K, 18K and 24K BTUs. Depending on the compressor's size, there are many combinations/configurations available. (Google Fujitsu AOU48RLXFZ for a quick preview.) Well, even though I haven't fully committed/decided to using mini-splits, at least I've done my homework. Thanks again!

Thanks for the education.  I (post #207324, reply #9 of 25)

Thanks for the education.  I have only seen the large surface mounted units.  The pieces I have seen written show these types and they aren't my style.  The one piece they wrote in the last week showed one surface mounted with the piping surface mounted as well and it looked about as attractive as running your plumbing on the surface of your walls rather than behind them.  I don't think it was a retro fit either.  I believe they did it intentionally to avoid losing some of the insulation value of the wall.

Surface Mount Plumbing (post #207324, reply #10 of 25)

I think I saw that article. It mention something about the gutter being in the way for the refigeration/drain lines. I was shocked to see the indoor pic. I don't think they did the 'industry' much good with that one.

Web sites like this one tend (post #207324, reply #11 of 25)

Web sites like this one tend to get upset when you start producing REAL numbers. Sort of inhibits a fair discussion. perhaps it's no accident that some firms - Fujitsu is one- try their best to keep everyone in the dark regarding pricing.

The result is: you need to get things quoted several ways to be able to compare.

I saw the Fujitsu 8-head unit. An interesting concept, one that appeals to me. Yet, I will use, for discussion, some publicly available prices to underscore my point. My source is Grainger's web site.

Let's, just for giggles, assume a 3-ton (35,200 btu) cooling load with three 1-ton heads.

Option A: Single unit with controls to operate three independent heads: Friedrich M36TYF1, $7215, plus line sets.

Option B: Three separate 1-ton units: Friedrich M12CH, $1670, plus line sets. 3 x 1670= $5010. Thats 40% less than using a single unit.

So what if you have three small condensers outside, rather than just a single large one? Who says they have to be in the same spot anyway?

Don't be dazzled by the technology.

Did you price out the same (post #207324, reply #12 of 25)

Did you price out the same size with a conventional AC and zoned air handler?  (No axe, just kind of curious how that would work out.  Of course, ductwork would be an issue, but ignore that for starters.)

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Technology (post #207324, reply #13 of 25)

I like your last statement. The trouble is that I work in information technology so its kind of hard to not be 'dazzled' by innovation.

You have made a point about costs - a point to consider for sure. However, aesthetics also comes into play. Do I want multiple consensors surrounding my house? Plus a generator? I think it might detract from the beauty of the house and the setting. There are always trade-offs.

we installed a mini split (post #207324, reply #14 of 25)

we installed a mini split system into a small house last summer and it did fine. i dont know about for where you are but in oklahoma the total instal price was around 3800 system labor new copper everything were a normal unit furnace and all would have ran upwards of 5500

Since we are into 'real (post #207324, reply #15 of 25)

Since we are into 'real numbers'...

Took a chance and bought a 19.2 Seer 1.5T mini-split heat pump off ebay for $1100.  (Klimaire, had no idea of the brand reputation and almost zero on-line reviews, but hundreds less than anything similar)

Other than my time and a few screws and scrap steel for bracket,  zero installation costs.

Since the OP is 'having a house built' vs building it, the time it took me to install was about 2 hours, not including the time or few cents power cost of leaving the vacuum pump connected overnight at 300 microns. PS: time and 'zero' cost not including the 240 vac power line to it - that adds another hour and $60 worth of CB/wire/disconnect, etc.

Interesting to see what others have seen as actual installation costs by a HVAC firm for a mini-split.  Probably the difference could buy more than one vacuum pump, micron gauge, etc.

Mini-splits versus whole house dehumidifier (post #207324, reply #16 of 25)

This discussion seems to have gotten away from the original question - would I be better off stepping up the compressor and adding a couple of indoor units in the lower level or installing a whole house dehumidifier?

I don't like the noise (post #207324, reply #17 of 25)

I don't like the noise produced by mini units and it doesn't allow the house to circulate air like a forced air system can.  One of the new whole house forced air systems with a variable speed blower can operate nearly silently and even if the house is cool enough I really like the air to be slowly circulating - it's a more even, comfortable house to be in.

If you aren't familar with variable speed blowers I would highly look into them - clients absolutely love them and it's like day and night as far as I'm concerned.

I have yet to see a mini unit that looks "right" .....  they catch my eye as being cheap even when they aren't cheap and they're built as as good as they can be.

If I could edit my location it would say I'm now in Reno :-)

And a non-trivial point is (post #207324, reply #18 of 25)

And a non-trivial point is that the variable-speed DC motors on your better whole-house AHUs are about 3 times more efficient than the old-fashioned fract-horse induction motors.  This can easily amount to $50/month in lower electric bills.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

DC blowers (post #207324, reply #19 of 25)

It's not just conventional AHUs that have variable speed DC motors. That's an advantage offered by mini-splits as well. As to heating, Mitsubisihi claims theirs can produce heat at around 0F, although at a lower efficiency. Big improvement over traditional heat pumps.

Andy Engel

Never try to teach a pig to sing. It wastes your time and annoys the pig.

Dry Mode (post #207324, reply #20 of 25)

Let me re-phrase my concern/question. Is the dry mode on a mini-splt system good enough that I can eliminate a whole huse dehumifier?

Grenn Building advisor suggest that a Daiken model is.

I'm not installing central A/C, so don't bother going there..



It depends. The safe answer (post #207324, reply #21 of 25)

It depends. The safe answer is no. But the right answer might be yes. You need to know the loads, the air leakage, and so on. Really sounds to me like you need a capable designer on the project.

Andy Engel

Never try to teach a pig to sing. It wastes your time and annoys the pig.

While we're repeating / (post #207324, reply #22 of 25)

While we're repeating / re-stating / clarifying ourselves ...

Your house has different areas with dramatically different HVAC requirements. No "whole house" solution will work very well.Mini-splits, properly sized, will be effective at removing the moisture. The key is to not oversize the units- at all. Far better that they be a bit undersize.

What you're ignoring is that your basement needs LOTS of fresh air. That's how you solve basement humidity issues. Bring in the fresh air from outside, and vent the old air outside.

you can only solve a basement (post #207324, reply #24 of 25)

you can only solve a basement humidity issue with fresh air if the fresh air is reliably dry enough.  in many (most?) areas of the country you could not reliably address a basement humidity issue with fresh air alone.  in a finished basement especially trying to do so is not only futile but extremely inefficient.  

dehumidification is often a more efficient and robust solution.  as much as I don't like reheating air conditioners... i mean dehumidifiers... typically.


Rockport Mechanical

HVAC Design and Installation in beautiful Rockport Maine

Update on mini-splits (post #207324, reply #23 of 25)

The GC had a sub lined up to install a ductless system. When it came time for the sub to start the work, he 'became difficult to reach'. So the GC is going in another direction. The problem is locating a sub that can do the application and is available ASAP.

So, I'm looking for a HVAC installer in Southeastern Mass that has ductless installation experience. That experience should include the configuring and installation of branch boxes, ceiling cassetts, and slim ducts.

Thanks in advance.

Lower level (post #207324, reply #25 of 25)

First of all, let me correct my own terminology; the subject area is simply the lower level to our house, not a basement. An upside down house if you will. It ls to be treated/conditioned like any and all other 'living spaces'; cooled, heated and ventilated.