ductless mini split heating and cooling

[explanade]

I like them, especially for retrofit solutions, but they are not perfect.

My biggest complaint is lack of filter surface and options to catch dust and other things. This can be "fixed" with an auxiliary filter unit if it is a concern -- you know, one of those units you stick on a table or in a corner.

I have some experience maintaining minisplits and discovered some irritating issues. In certain conditions, they could get moist inside and catch dirt on the condensing moisture. This would eventually cause a disgusting black layer build up on some smooth internal surfaces. After a period of low use (spring/fall), the next time the fan kicked high, chunks of crap would fly out.

It is difficult to take apart and clean these areas. What I've read is that you can fix this issue by forcing the fan to run a bit higher or longer, which stops the internal condensation issue. Oh, and this is really only a problem in very humid areas like Southeast USA.

I think installers are learning how to deal with them. Like so many smart devices, there are a slew of configurations that must be done for a good install. Most of these are hidden to the end user. The defaults are not always appropriate for every application. Good installers know what to do.

Hmm, could the black stuff be mold spores?

It could be spewing out spores before you can tell because they could be microscopic but you could still inhale them.

 

[wolf]

We are building a house and the main part will have standard ducted HVAC. There is a guest bedroom over the garage, about 400sf. and the HVAC contractor recommended using a mini-split there due to the difficulty and length of duct needed to reach it. He says that they are by far the most efficient heaters because they are pumping the heat from outside, not creating it with electricity or flame.

He just built a new house for himself. He has heated (slab) floors and two or three mini-splits for AC and supplemental heat. So he is a believer.

Can you post: The brands, the contractors recommend ?

Thanks.

 

[explanade]

So they don't need ducting but they have some kind of lines to drain fluids and have some access to the outside?

Because I think I've seen them installed in interior walls, so not even adjacent to the outside.

 

[OldShooter]

Can you post: The brands, the contractors recommend ?

Thanks.

Sorry. They are still framing the house. No idea yet about what brand is the HVAC guy's favorite. If I find out before this thread dies I will update.

 

[NW-Bound]

So they don't need ducting but they have some kind of lines to drain fluids and have some access to the outside?

Because I think I've seen them installed in interior walls, so not even adjacent to the outside.

Well, an AC's condensate has to go somewhere.

It is possible to mount them on interior walls, but the drain line then has to be concealed in the wall, then going down the drain somewhere, or draining outside.

They now have ceiling mounted air handlers, which have the line running right above the ceiling and going to the outside.

 

[ncbill]

Living here in south Louisiana AC's are still being installed with the evaporator and ductwork in the uninsulated attic. The ductwork is made from 1/2" rigid insulating board (if that thick). And yes it gets hot here. So much that it's difficult to find anyone willing to work in your attic in the heat of the summer. When the AC starts up there is a brief shot of hot air before the cooled air comes out of the ducts.
But that's the way it has always been done. I hate when I hear that. The resistance to mini splits from the AC contractors is incredible. They hate them because of the ease of installation and they work so well. They can't overcharge customers like they can for a central AC installation.
My DS just had one installed in a master suite addition. I told him that we could install it ourselves easily. (I've done some AC work in the recent past and feel confident that I could do it) He had his AC contractor install it. It only took him 4 times to get it right. He made so many simple mistakes that the last time I was there watching him. When I saw the fitting that he had to cut out and solder in a new one I was amazed. It was twisted and leaking because he didn't backup the fitting he was tightening onto.
Years ago there was an AC guy in New Orleans that was advocating for building an insulated air conditioned box around the evaporator in the attic. He claimed the unit would last longer because of less thermal changes and would work less since it wasn't fighting against the extreme heat. The local AC contractors hated him and basically put him out of business. And they're still installing the evaps. in the attic!
Resistance (to change) is futile!

IMHO, it's just poor building design.

My townhome in its finished basement manages to carve out both a laundry room and mechanical room next to that which houses both the gas water heater & HVAC air handler for the heat pump (gas furnace with A-coil on top).

No worries about the condensate drain clogging, overflowing the catch pan in an attic installation, and then ruining the ceiling beneath.

 

[NW-Bound]

I like them, especially for retrofit solutions, but they are not perfect.

My biggest complaint is lack of filter surface and options to catch dust and other things. This can be "fixed" with an auxiliary filter unit if it is a concern -- you know, one of those units you stick on a table or in a corner.

I have some experience maintaining minisplits and discovered some irritating issues. In certain conditions, they could get moist inside and catch dirt on the condensing moisture. This would eventually cause a disgusting black layer build up on some smooth internal surfaces. After a period of low use (spring/fall), the next time the fan kicked high, chunks of crap would fly out.

It is difficult to take apart and clean these areas. What I've read is that you can fix this issue by forcing the fan to run a bit higher or longer, which stops the internal condensation issue. Oh, and this is really only a problem in very humid areas like Southeast USA.

I think installers are learning how to deal with them. Like so many smart devices, there are a slew of configurations that must be done for a good install. Most of these are hidden to the end user. The defaults are not always appropriate for every application. Good installers know what to do.

The same problem can happen with the traditional central HVAC. The difference is that the evaporator where the condensation takes place is not visible and accessible to the owner. He would not be aware of the problem he is having.

My Pioneer units have a filter which has a fine nylon mesh. I take them down each year and use my vacuum cleaner to get the dust off.

One year, I procrastinated and happened to notice the airflow was so weak. The filters were all clogged up!


PS. Because the mini splits are ductless, they can provide a much stronger airflow than a central HVAC. The air ducts have more resistance to airflow than you imagine.

 

[OldShooter]

Well, an AC's condensate has to go somewhere.

It is possible to mount them on interior walls, but the drain line then has to be concealed in the wall, then going down the drain somewhere, or draining outside.

They now have ceiling mounted air handlers, which have the line running right above the ceiling and going to the outside.

The ones I have looked at for our new house are 2-piece units. The inside unit is connected to the outside unit via go-and return-freon pipes, a condensate drainage pipe and a control cable. Distance between the units can be quite large. IIRC I saw one where the limit was 80 feet of piping.

Re ceiling mounted I was quite excited when I found those in-ceiling units, but found that they require a lot of space, more between floors than typically exists and 24" between trusses/joists. They also must be insulated sides and top according to our builder. Bottom line for us was to use them would have required structural changes to the house.

 

[JoeWras]

Hmm, could the black stuff be mold spores?

It could be spewing out spores before you can tell because they could be microscopic but you could still inhale them.

Yeah, I know everyone worries about that and it causes panic. In this case, it didn't appear to be black mold. I've worked with that stuff before in my disaster relief.

Instead, you could see the dirt "blow-by" beyond the filter. Was there a bit of mold too? Probably, your typical garden variety. Anything is possible.

 

[NW-Bound]

The ones I have looked at for our new house are 2-piece units. The inside unit is connected to the outside unit via go-and return-freon pipes, a condensate drainage pipe and a control cable. Distance between the units can be quite large. IIRC I saw one where the limit was 80 feet of piping...

Yes, that's how they all are connected, including traditional split HVAC units. The compressor/condenser is the exterior unit, and the evaporator (air handler) is the interior unit. In the heat pump mode, the role is reversed.

The difference with a mini split is that the interior unit is always wall mounted (except for the new in-ceiling type). The exterior unit is usually wall mounted, but can be ground-mounted if so desired.

 

[mountainsoft]

I installed a Mr Cool 24K mini-split in our 1456 sq/ft house last summer. I originally installed it because we didn't have any kind of air conditioning for hot weather. However, I only used it in AC mode for one day before switching to heat mode.

We have individual wall mount electric heaters in each room, so we don't have any existing duct work. I only expected to use the mini-split as supplemental heat to our wall heaters, but was surprised we could heat our entire house with it all winter. When temps got down in the 20's or 30's outside the wall heater in our master bedroom (furthest from the mini-split) would sometimes come on, but otherwise the mini-split handled the entire house.

We also noticed a minor reduction in our electric bill too. It wasn't a drastic change, but certainly less than we had been using. It's also quieter than our wall heaters with fewer drafts and temperature swings.

Once temps get below freezing outside the outside unit has to run a defrost cycle periodically, but otherwise it still heated fine in 25 degree weather.

The mini-split is now our primary heat source, supplemented with our original electric wall heaters if needed, with a wood stove as backup when the power goes out.

 

[otodd]

I investigate briefly about a year ago, and there are "new" systems effective to below zero. My project is on hold, for now. A local utility is now promoting splits with rebates, in an area that frequently goes to zero F, and occasionally to minus 15.

"New" may be a few years ago, but they seem to have matured and validated more recently.

My interest was mainting a central gas furncace, with a DC motor and 2 stage gas valve. The splits would be complimentary heat and the source for A/C.

 

[gooddog]

Have had quite a few of the mini-splits. There are some advantages, and some disadvantages. The big advantages are ease of installation, and cost. There are multi-head systems that work off one condenser, but if you were looking at something like that then might as well go with traditional HVAC. There mini-split systems that are precharged with freon that you can install yourself in about "3 1/2 hours" - takes 5 hours. "Mr. Cool" is one of those systems. If you are looking to have a mini-split installed, I would highly recommend a Mitsubishi unit. Had both Mitsubishi and Daikin, and found the Mitsubishi to stand up to corrosion from the ocean climate much better. The boards are very expensive when they get fried, so put an in-line fuse (which will also act as a disconnect) to protect the unit. The units are not nearly efficient as claimed in my experience.

 

[arch57]

We have a second home in the foothills of Western Maine and yes it does get very cold in the winters. We installed a Mitsubishi HyperHeat (-13 deg F rating) mainly for the air conditioning but were pleasantly surprised at how well it did as our primary heat source this past winter. The variable speed technology is really amazing and both the outdoor unit and indoor units (we have 2 zones) are very quiet and being a retired electrical engineer the control algorithms to provide comfort and efficiency are very well tuned.

We saved about 40% over the cost of propane this past winter and we had a few zero degree nights while we were up there and were comfortable enough. I highly recommend them.

 

[zippy2020]

frank, you might want to check the cost of having a HVAC company do a pressure test - our state makes it mandatory, but obviously state laws vary. Our HVAC co. told us we just about made the limit for leakage before an A/C install. 15% or greater leakage requires replacing the ductwork = $$$$$. We were at 12-13% on ductwork installed in 1989.

 

[pdxgal]

The mini split does reduce humidity. It has a condensation drip tray, just like a whole house type evaporator, and the condensate water is drained outside. The drain line typically runs with the refrigerant lineset and drains near the outside condenser unit.

Finding an installer who knows what they're doing is especially important. A lot of HVAC companies have jumped on the mini-split bandwagon recently, so I'd look for experience.

A neighbor had a mini-split installed by a local big name HVAC company that has tons of experience with furnaces but not so much with mini-splits. After a year the neighbor discovered the basement wall below the condenser was damp and moldy. Turns out condensate wasn't draining properly away from the house. Lots of arguing with the installer ensued, but they finally did correct the problem and pay for basement wall tear-out and repair.

I had mini-splits installed in both the upstairs month-in-law unit of my house, and my rental property. They work great, and save about 50% in winter vs baseboard heating. And having AC is a great plus now that heat waves in the NW are more frequent. My tenants love them. When my 24 year old gas furnace bites the dust I plan to install a heat pump that will use the existing ducts.

FWIW I used an installer that specializes in heat pumps. They really know their stuff AND they were slightly cheaper than the bigger, more established HVAC contractors.

 

[Rambler]

I know lots of you have newer homes and was wondering if any of you have the ductless mini split systems for cooling and heating and what are your reviews on them. do you think they are better than the standard ducted system or less efficient and cost effective? thoughts?

We had them when we lived in Japan. The cooling worked great, but the heating was only ok if it wasn’t below freezing outside. That’s been a while back…may be better now? I don’t know. We are adding a 2.5 ton (maybe 3 ton, TBD) single compressor, double head unit for our RV garage in the Phoenix area. We don’t intend to “refrigerate” the garage, per se, but keep it to perhaps the mid-80s for loading and unloading times, with the occasional drop to mid 70s when we use the home gym out there during monsoon.

 

[NW-Bound]

We have a second home in the foothills of Western Maine and yes it does get very cold in the winters. We installed a Mitsubishi HyperHeat (-13 deg F rating) mainly for the air conditioning but were pleasantly surprised at how well it did as our primary heat source this past winter. The variable speed technology is really amazing and both the outdoor unit and indoor units (we have 2 zones) are very quiet and being a retired electrical engineer the control algorithms to provide comfort and efficiency are very well tuned.

We saved about 40% over the cost of propane this past winter and we had a few zero degree nights while we were up there and were comfortable enough. I highly recommend them.

That's very good!

 

[Old Microbiologist]

We retired to Europe and like most of the world, with the exception of the US and Canada, all heating and A/C are done using systems not usual to the US anymore. Heating can take the form of radiators or in-floor heating using heated water which can be either electric or gas (or oil) heating. The EU has mandated all boilers (here called a Kazan) must use condensing boilers which capture toxic gasses and all potential heat loss throiugh the exhaust.

A/C is actually fairly rare in Europe and only "rich" people have them. But, they are becoming more common as the costs are relatively low and installation fairly simple. We installed 3 in our first house, one being 5,000 watt (cooling the downstairs) and the other 2 in upstairs bedrooms at 2,500 watts. The other house has 4 2,500 watt units. They work remarkably well as both air conditioning and/or as heat pump heating in case the gas supply is interrupted. I don't see a huge impact on our electric bills when we switch over or add supplemental heating in winter. In general though we don't use them unless the interior temp gets above 30 degrees C (86 F). Europeans prefer to open windows for ventilation. So, in general you don't encounter systems inside homes at all or any government buildings including hospitals. Even lighting is used sparingly.

I will add that in Europe all windows have installed thick metal roller blinds that add a lot more insulation (and darkness) which is also something not seen in the US. It is kind of weird to see now lights on in any homes in the evening. Our house being a strange custom built home (not by us) has rounded top windows that cannot accommodate the roller systems and we have very large windows in several rooms that are enormous (and high) so can't have them either. We stand out as having our home seen by the world which is "weird" here.

 

[werdone]

Mini Split and Geo thermal

Frank,

I have had a 1500 sq ft ranch with electric heat and no air in Ohio I used a multi head mini split to cool and sometimes dehumidify the house. It was a low cost quick install and the electric increase minimal. Newer mini splits are very efficient but the heat is a resistive heat and worked ok. I currently run a single zone 12K off 1400W of solar and we have been in 90 to 95 heat all week in an RV. (poor insulation).

I have also had a 5000 sq ft house we built with a Geo thermal system installed. My install was the lateral install no pond(most efficient). I had a friend that went with the vertical well install and he typically saw a 6-8% better efficiency than I did. The lateral is cheaper to install and maintain if needed. If you can find an installer that has their own drill rig it helps on the install cost for the vertical. He had them drill and cap a spare well for the future at very little additional cost. Our air and heat bills were less than our bowling couple friends with 3200 Sq ft houses and close to friends that had brand new 2200 Sq ft houses.

Good luck with which ever option you go with.

 

[explanade]

Staying at a vacation apt. in Antibes, France now.

It has one of the ductless mini splits.

It's on a wall adjacent to another house -- they're kind of like row houses in a narrow alleyway, too narrow for cars.

Been using this ductless, a Samsung with "Digital Inverter Technology" labeled on the front.

Had the AC on for about an hour after returning from the day. Then turned it off.

But just heard some warbling in the wall where this ductless unit is mounted. Like some water draining in a large pipe, with the water moment kind of echoing.

Hmm, is it typical? Maybe it takes awhile after use for the condensate to build up and then drain kind of at once?

 

[freedomatlast]

The condensate shouldn't drain all at once, but I'm betting what you heard after you turned the system off was the pressures between the suction side and the high pressure side of the system equalizing after the compressor shut down. This can make the sound you described and is completely normal.

 

[lauradrops]

We had Mitsubishi mini-splits installed in our Cape renovation. Didn't want the ducts in my basement and too hard to put behind the attic knee wall.

They absolutely dehumidify the air.

We love them. They are much quieter than my central air was in my last 2 homes. I also really like that I can put my bedroom into a deep freeze at night without affecting the rest of the family.

We have found them much less expensive than any other AC. We don't really use the heat because we have gas hot water heat through a Navian which is super efficient. But on a really cold NY winter day, I will use it briefly after I've been out to take the chill out of the room as the heat comes up.

I will say if you go mini-split it is very important the installer is properly trained. Proper sizing is not as easy as you may think. We used a Mitsubishi Diamond Contractor which I believe ups our warranty to 12 years. He was also much less expensive than the other companies who quoted me Daikon units.


We also got a $750 rebate which was nice.

 

[JoeWras]

I will say if you go mini-split it is very important the installer is properly trained. Proper sizing is not as easy as you may think.

Very true.

The non-profit I help out with got oversized units and they simply could not dehumidify enough. It cooled too quick.

 

[NW-Bound]

Very true.

The non-profit I help out with got oversized units and they simply could not dehumidify enough. It cooled too quick.

With a variable-speed compressor, raising the temperature setting up a degree or two will cause the compressor to go into a slower speed and reduce its cooling capacity. I wonder if this helps.

I can also dial down the blower speed of the indoor unit. This should slow down the airflow to increase the condensation of moisture for dehumidification.

The above said, I often crank the blower speed on high, because it's so dry here, and I also want a strong air circulation to achieve an even temperature inside the home.