Ductless Mini-split Heat Pump

daisyblueFebruary 12, 2013

I'm curious if anyone else is choosing/has chosen this option? If you currently have a mini-split, I'd love to know how well it performs and whether you like it?

We are designing our home (located in western NC) to take advantage of passive solar and to be relatively efficient/air tight. It will also be all electric with the goal of installing photovoltaic panels if/when they become affordable to us.

Thanks for any input!

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Hi DaisyBlue, congrats of doing some good research. There is definitely an increasing trend of using Mini splits in high performance homes these days. Whether it makes sense for your home depends on the details.

I havent done a system yet but Iam looking forward to the right opportunity. They are suited best to small and open floor plans. I feel that the tipping point between minisplit and conventional is when the home has three bedrooms or more, especially with two floor levels.

Usually in homes of this size, three different units are needed but the multi-head systems are beginning to overcome this limitation. With 3 units at $2.5-4.5K a piece, its usually cheaper to do a conventional system with ducts.

If your home is open enough and you can get by with one or two units, keep in mind that bedroom doors generally need to be left open. Another drawback for a lot of people is the aesthetics. They are pretty low profile but still need a suitable spot for the indoor fan and outdoor compressor.

Perhaps the biggest drawback in all but the most open of floorplans is that there may be a loss of control over the indoor air quality. Its nice to have the mechanical ventilation ducted to the bedrooms to ensure that occupants are getting fresh outdoor air where they most need it. You could have both but that negates some of the cost savings.

If you are going passive solar and PV then energy efficiency is obviously important to you as it should be. You need to focus on your Bulding Envelope above all else. "Relatively" airtight and efficient is not the most cost-effective path to low energy costs.

The high performance homes that are using only mini-splits are generally extremely air-tight and continuously insulated. You should ensure that your building envelope is at least up to IECC 2012 codes but I would try to go further. Here in WNC, most inspectors and builders are still way behind when it comes to meeting this basic energy code.

The building envelope is the most permanent part of the structure and hardest to improve once complete. It also has the biggest impact on energy costs and can make a huge difference when relying on passive solar and mini-splits. Your research is going to pay off in an amazing home.

    Bookmark   February 12, 2013 at 11:17PM
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I have 2 separate systems--one with dual interior heads (LG, about 4 yrs old), and one with ducts (Mitsubishi, about 2 months old).

They perform great for my greater Seattle area house.

You'll find a lot more information on this topic in the HVAC forum...

    Bookmark   February 13, 2013 at 12:33AM
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I'm intending to go this route on our build in Portland OR. Probably could get by with 3 heads but might go with 4 just for zoning and the fact that my husband likes to sizzle in his office while I'm fine freezing in the rest of the house. Even tho the climate there is quite mild, I knew my hubby would insist on some form of AC thanks to heat production from a fair number of computers, and the system does both which is a big plus. Based on all my research the operating costs are pretty substantially lower which we're looking forward to and hopefully might offset the initially higher install cost

    Bookmark   February 13, 2013 at 2:16AM
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OT - in NC not affording PV is probably akin to not being able to afford building a house.

Lets see - 30% fed credit, 35% state and utilities with renewable mandates. I just signed for 26 panels for a net cost of $7k. The ROI is well above 10%.

Have you been to competing forums where there is a lot of talk on ductless? With the word "green" and "building" in the title. You will find much more info there.

All electric is great and all but I wouldn't give up NG if I had access to it. I use less that $200 a year but it really gives flexibility.

The other "challenge" in NC is the geothermal credit. If you really want all electric and low running cost, you should be able to make geo work. Again a 65% tax credit makes it work if you can get a reasonable install cost. There is no tax credit on mini-splits.

But I'm not sure getting all fancy is worth it.... R20 net walls, good southern exposure with some thermal mass. You won't need that much heat and you shouldn't need a/c (although I am just guessing on what Western NC means).

I considered mini-splits - the aesthetics were never going to work. Also with 4 bedrooms and 3 floors, it would have cost some money that never would be recouped.

I've thought about this a lot and I don't know how cold you get but if you have total control of design and southern exposure, your best bet is lots of solar planning, tight house with thick walls. Cover the windows well at night. Then put the money in PV. Code will require too much of minisplits to be cost effective.

    Bookmark   February 13, 2013 at 3:31AM
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On the west coast, minis are the way to go if no NG... We have no subsidies for Geothermal and astronomical costs. However, on this forum, many people on the East Coast find Geothermal to be quite attractive in price. Apparently those states have lower costs to install as well as substantial credits/rebates.

    Bookmark   February 13, 2013 at 2:53PM
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I really wanted ductless, but unfortunately we went a different route. I think the ductless is more common in western NC than here in central NC. I know it is more common on the coast.

OT - in NC not affording PV is probably akin to not being able to afford building a house.

Not really. If we put those same 26 panels on our house it would cost us $14,000 since we would not get the 35% state credit. It really depends on the individual situation.

    Bookmark   February 14, 2013 at 12:49PM
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I'm going with ductless on our small home in upstate SC. There will only be two heads for now, and the house is so well insulated that it would be hard to find a small enough ducted system. I think they have merit for the right kind of house, in the right climate.

As for aesthetics, they do make ceiling units for minis that look like a regular A/C duct, but they are considerably more expensive. I'm going to go with regular wall mounts, with an eye towards ceiling units if and when they come down in price.

    Bookmark   February 14, 2013 at 3:43PM
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Fair enough on the tax credit but since most people pay taxes... You do know it can be spread over 5 years so anyone making over $60k or so probably can use it all?

    Bookmark   February 15, 2013 at 6:16AM
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Yes, I know it can be carried over, but 5 years is not long enough for us to get it all.

And then there are those who are building a vacation home in NC, but are residents of another state.

Also, since these are tax credits, you have to be able to afford the panels first and then get the credits later. Not everyone can afford the up-front cost.

    Bookmark   February 15, 2013 at 9:12PM
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Agree it is hard to beat the economics and the efficiency (I'm on the west coast) but I could not get past the aesthetics myself. If only they were invisible! The only ones I've seen are big white boxes mounted way up on the ceiling. We don't have a lot of wall space as it is and I couldn't bring myself to consider them for long.

    Bookmark   February 16, 2013 at 10:07PM
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Thank you for the responses!

Brian Knight ~ Our home is one level (on a slab) with three bedrooms. It will be an open floor plan, just over 2,000 sq.ft. When I said "relatively" air tight/energy efficient I was referring to our quest to balance efficiency with using healthy materials (not a fan of spray foam for example).

We do want to be mindful of proper ventilation/air exchange and have looked into doing something like this (copied from http://homeenergypros.lbl.gov/group/1000homechallenge/forum/topics/panasonic-whisper-green-w-ductless-heat-pump?xg_source=activity):

"Some minisplits may have a small ducted system. Dave Robinson, www.GreenEarthEquities.com buys foreclosed homes in central California that he renovates, using two,1 ton Fujitsu mini-splits. He ducts one to the bedrooms and bath with very limited ductwork located in the hall ceiling. The other unit is ductless, and conditions the living room and kitchen of the one-story ranch homes. There are significant cooling loads with lots of 100 degree weather. His approach of combining ducts and ductless results in simple systems and homes with low energy bills. Dave has case studies posted on his website."
Reply by Dave Robinson on August 31, 2011 at 10:12am
"To be more exact, we use one outside unit (2 ton is the smallest they make in this model - so we use it on everything). One inside unit is the conventional mini split high on the side wall in the main room ... the one that everyone associates with mini splits. The other inside unit is mounted on the ceiling at the mouth of the hallway & delivers air to all the rest of the rooms thru a small duct system that we mount on the existing ceiling of the hallway. So the unit and all the ducts are inside the envelope. Then new drywall is added, reducing the hallway height about 10 inches. We throw the factory filter away and allow a 20 x 30 filter grille right under the air handler to provide a lot more filter area as well as access to the unit without breaking the building envelope. You can see pics of this hybrid duct design at A Good Business? How Long? Plus Ducted MiniSplit Update (Click the right arrow on the photo in the center of the page and it will take you thru a few other slides from that webinar and you'll get to the Mini Split photos). You'll notice we use galvanized pipe. That, along with the oversized return keeps the static way down which is essential for efficiency on these units. This unit has now been in two years. The owner loves it. Zero problems. Has utility bills less than half of his neighbors.

This job also used a Panasonic ERV. We mount the ERV very close to the return of the ducted system and in the pick-up area of the wall mounted unit so all fresh air is circulated by the main system with no additional equipment needed. It works well for us and we have adopted this as our main system. It's the one we specify every time unless we are keeping old equipment that's not too old or too over sized for after our renovation. You'll also notice that we mount the outside unit on the roof instead of on the ground. Lots of reasons."

We are thinking this might work with our floor plan:

Kirkhall ~ Thanks for sharing your personal experience. I have read more on the HVAC forum. My interest in posting here was to see if ductless mini-splits were at all a preferred choice by those building new homes versus just being used for retrofitting/new additions.

Niteshadepromises ~ "Based on all my research the operating costs are pretty substantially lower which we're looking forward to and hopefully might offset the initially higher install cost." This is in line with what we are thinking too! Good luck with your build!

David Cary ~ The tax credits are wonderful, however, there is that pesky problem of having to pay upfront. With some budget reworking, this may be possible. However, my concern relates to your comment,

"But I'm not sure getting all fancy is worth it.... R20 net walls, good southern exposure with some thermal mass. You won't need that much heat and you shouldn't need a/c."

We don't want to pay for more than we need. The difficulty for us has been determining what our need is when factoring in the passive solar.

I also agree with:

"I've thought about this a lot and I don't know how cold you get but if you have total control of design and southern exposure, your best bet is lots of solar planning, tight house with thick walls. Cover the windows well at night. Then put the money in PV. Code will require too much of minisplits to be cost effective."

To satisfy code, what would your recommendation be for a thermostatically controlled system that is reasonably efficient and cost effective (presuming we could swing the PV)? With good solar planning, another viewpoint is to put in some baseboard heaters to satisfy code. Is this reasonable or silly?

Dekeoboe ~ I'm interested to know what you chose and why?

Flgargoyle ~ As our heating and cooling days are very similar, it's good to know that you think it's a viable option. Though it seems I'm in the minority, I don't really mind the look of the wall units. Maybe it's because I don't find vents and returns all that pretty!

Lori in the NW ~ Thanks for your opinion ~ they certainly are not for everyone!

This post was edited by daisyblue on Fri, Feb 22, 13 at 17:45

    Bookmark   February 22, 2013 at 4:53PM
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daisyblue - I really wanted mini-splits. We have no problem with the aesthetics of them; I really don't think they look any worse than vent covers everywhere. Plus I really dislike blowing air. We ended up with geothermal. Mostly, our choice was driven by the fact that the first well we dug ended up being a dry well. Since we had to pay for that hole in the ground, we decided to put it to use. If we hadn't had that dry well, I am pretty sure I would have had my mini-splits. Our builder has used them before.

    Bookmark   February 22, 2013 at 8:36PM
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Dekeoboe ~ My husband and I do not like blowing air/dust either. We have also looked into radiant heating and cooling, but are unsure that it best fits our application. I agree with you regarding the aesthetics of mini-splits, in that I think they look better than the numerous supply and return covers.

Digging the dry well had to be frustrating. I hope the geothermal is working out for you.

    Bookmark   February 22, 2013 at 8:50PM
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My experience is also relevant to you, though. I had the choice, when we did our "addition" (it was extensive, and involved the whole house) to put in a regular NG furnace system or the minisplit. The utility company actually advised us to do the minisplit. We were familiar with them already so didn't have the negative associations that some people on here do.

We did ultimately, get the second system, and it essentially is what is described in your copy/paste above. I call it a "ducted ductless". And, it serves all our bedrooms (4) with one exterior unit/one interior unit. Our interior unit is not visible from anywhere. The thermostat is remote controlled, so we can mount it on the wall like normal, or, as we are painting right now, it can be in a zip lock baggie...

Works great so far!

    Bookmark   February 22, 2013 at 9:27PM
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I have had a Mitsubishi mini-split unit for several years in WNC, and do not recommend it. Twice, the entire system has stopped working and had to have the main circuit boards replaced. Even at top form, when the winter temps drop to 20s and teens, the units will not heat the house above 63 degrees. After investing $11 K on this system-due to no ductwork in my existing home-I have installed a woodstove to make up for the lack of heat in the coldest months.

    Bookmark   March 9, 2013 at 11:06AM
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Kirkhall ~ Please accept my apologies on two counts: One being that I somehow missed seeing your Feb. 22nd post and two that I didn't communicate my thoughts properly regarding new builds vs. additions/retrofits. Your experience is very relevant to me! What I was trying to explain is why I posted this question here instead of the HVAC forum. Comments from builders in my area indicate that they are familiar with mini-splits being used only in additions and retrofits. The consensus seems to be that mini-splits are not a first choice when building a new home. It's good to know that they have really worked well for you! I hope your painting turned out well and that you are enjoying your new space!

Mbippy ~ Thank you for sharing your experience. I'm sorry to hear that it has been a negative one. Hopefully that woodstove kept you warm and cozy this past winter! We continue to explore all options...

    Bookmark   March 17, 2013 at 10:01PM
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