Mini split recommendations

[DonTee]

I’ve been thinking about getting a mini split for my house. I have some questions about what’s the best unit, and if what I want to do will even work. I’ll tell you about the house first, and then what I want to do.

House is about ten years old. It’s wood frame construction with 2x6 walls, decent insulation, and decent windows. The house is pretty tight. Around 1500 sq ft.
It’s located in upstate NY. Right now the only heat source is a wood stove.

First of all I need to get home owners insurance on the house. I used to have it years ago, but let it lapse. I’ve been telling my wife I’ll get it again before wood burning season. The insurance I had before was more of a construction insurance.

I need to have some other primary heat source besides the woodstove. Not that I would actually use it as a primary heat source, but for insurance purposes. Would the mini split work for this?

Second, there are times when I have to leave the house on short notice. Usually not in the dead middle of winter, but I can’t rule that out as something that will never happen. I know the heat pump will not work below a certain temp. Of maybe it’s just super inefficient IDK. I’m not sure if some mini splits have heat strips in them as well. Anyways, I need something that could keep the house above freezing for short periods of time during the winter.

3rd. On hot summer nights my kids would like it if I could cool down the house a little. It doesn’t have to be an icebox, just cooler and less humid.

And last, during shoulder season it would be nice to not have to fire up the woodstove on days when it will warm up shortly.

Basically my house is almost a square. It’s 24x30 and two story. When heating with the woodstove in the winter all rooms are very close to the same temp. I can keep downstairs 75ish and upstairs 77ish. The plan is to put the mini split blower unit in the middle of the house. I think maybe in the stairs between the floors.

Can you guys recommend a brand(s) and size unit? Thanks.

 

[DonTee]

Reading this thread it does look like the mini split would heat down to the low temps here. The lowest is usually around -15.
In that thread the OP said his mini is rated down to -22.

Mini Split Heating at -8F

Mini Split Heating at -8F In another recent thread, the subject of mini splits and heat pumps came up tangentially in a heating context. I have been heating for two seasons at my new house with a mini split, and this may be one of the last times I can report on cold weather performance with the...

www.hearth.com

 

[Highbeam]

It’s super cheap and almost universally accepted as a primary heat source to pop in a few cadet wall heaters. Straight electric. Zero maintenance, last forever, thermostat controlled. Electric cost is based on local rates, very common here in the pnw.

 

[DBoon]

Yes, a mini-split will work in your home and your climate, but I would suggest that you not to try to have it do everything, i.e. don't size it to be too large and don't try to make it heat when it is the coldest day of your year.

Mini-splits that heat down to 5 degrees F are pretty common and have higher coefficients of performance (COP) when it is warmer than mini-splits that heat down to -17 degrees F or so. If you just need emergency backup below 5 degrees, consider also electric resistance heat as a fail-safe should the house temperature drop below 40 degrees and you are not there. Mini-splits don't have backup electric heating elements. I would recommend the mini-splits that provide heat to 5 degrees F - their efficiency gains during the majority of the heating seasons compared to the -17 degree F units will make up for the few times a season you might have to run electric resistance heat when you are not there to run the woodstove.

A central location will work well for a single mini-split. Heat rises - for heating it will be best on the first floor and for cooling best on the second floor. If you are only going to get one and you don't really need the AC, then it should located on the first floor.

I've owned both Fujitsu and Mitsubishi mini-splits. They both work very well and they both make units that operate in very cold (-17 degree F) weather, if that is what you really want. I think these are the two premium brands (with premium prices). Others have used other brands (LG and Daikin come to mind) and seem satisfied with them.

 

[EbS-P]

What’s your budget? Given your use case spending extra for efficiency might not payoff like it does for someone who will use for 100% of those heating and cooling needs. There are DIY units the come with evacuated lines and quick connect fittings (look up MR cool) but they aren’t as high quality as a Mitsubishi with hyper heat. MR cool do not turndown as low as the Mitsubishi and Fujitsu units. But Costco is selling a 12k btu (120v) unit shipped for 1100$. Saw an add for the 4th gen mr cool units but haven’t looked at specs.

I probably would not go bigger than 18-24 k btu. And as long as the units lowest output doesn’t run you out of the first floor bigger is ok (to a point). And sizing for heat is probably more important. A smaller top tier cold climate heatpump would be better suited for you but you could buy 2 or 3 mr cool 12k units.

Just my thoughts

 

[DonTee]

Thanks for all the good input. I was hoping to spend 2 grand or less. A unit I could install myself without calling out an HVAC guy is a bonus.

Like I said, this would be a backup system in case I have to leave the house in the winter for some reason. If I have to leave for longer than the woodstove will last.

Having a smaller wall unit is a big plus for WAF. I just need something that will keep the house above freezing if need be (50-55 degrees?).
And the AC part would probably be used like a dozen times a year.

Unit efficiency is a plus, but with the amount will use it, it’s not necessary to have a super efficient unit. Especially if it will add substantially to the cost.

 

[EbS-P]

I’m not sure you can get any name brand unit for 2k. Install would likely be another 1000$ just guessing. I have a quote for a 15k Mitsubishi that was 5600$. 6000$ if I wanted the cold weather hyper heat model.

Mr cool 18k btu might do it. Not sure if it’s the right size. Look at the lowest output between the 18 and 24 Kbtu units. Both are 240v units.

I use this site to look specs up. Looks like they have dual head single compressor units now available in the DIY line. Not that it matters. To you but it might.

https://ashp.neep.org/#!/

 

[DonTee]

Besides buying the unit itself what else would I need?I know I’d need a new breaker in the power panel and wiring to the unit. I have some stuff left over from when I wired my house I can use.

I assume the Mini split comes with the hose/wiring that connects the inside unit to the outside unit? Anything I’m forgetting?

 

[begreen]

For peace of mind, I would include a second circuit for a resistance-style baseboard or built-in wall heater. That will be the equivalent of a strip heater in a ducted system. It can be connected to a low temp thermostat set at say 45º to prevent pipe freeze-up in the event that you are away.

Moved to the DIY forum where there are many other mini-split install threads here for more tips. Search on mini-split, title only, in this forum.

 

[EbS-P]

Besides buying the unit itself what else would I need?I know I’d need a new breaker in the power panel and wiring to the unit. I have some stuff left over from when I wired my house I can use.

I assume the Mini split comes with the hose/wiring that connects the inside unit to the outside unit? Anything I’m forgetting?

Bracket to mount the compressor unit. Exterior disconnect. Hole saw to cut the right sized hole. If I did it it would be an excuse to buy torque wrench for the fittings.

 

[gthomas785]

I have a Pioneer mini split that I got mostly for backup heat, but I gotta say we have ended up using it a lot more than we thought we would. It's just so efficient and convenient. Especially found using the dry mode in the humid months of August and September to be life changing. And it added a whole $20 to my electric bill.

For heat, it works great but I did notice the output drops off when it's below ~15f out. It says it will heat down to -5, which it will, just that there's less heat coming out right at the moment when you wanted more heat.

Keep in mind that the system will actually dehumidify better if it's slightly undersized, and will remove less moisture the more oversized it is (per btu of sensible cooling). So in cold climate where you sized the system for heating it will most likely be oversized for cooling and not dehumidify as well. Somewhere in here is an argument for having 2 small systems as opposed to 1 larger one. Or just get a smaller one and accept that it won't keep up when it's -17 degrees out.

Anyway, if you want 100% reliable backup heat, get electric baseboards. They cost very little to install and give you peace of mind, and there's no question whether your insurance will accept them. Set them to off unless you leave the house. I'd get a couple of those in addition to the mini split.

 

[DonTee]

I hadn’t thought about the dehumidifier aspect of it, but yes that’s a good point.

Like I said, part of what I want to do is to satisfy the insurance company, but the other part is to have a system that’s reliable if I have to leave the house for some reason. The reason why I’m leaning towards the mini split instead of just baseboard heat etc is because it’s useful in many more ways.

Basically the selling point of this system to my wife is that it only takes up the one space on the wall. I might have to buy the mini split and test it out this winter to see what it can do. Then if it’s not enough I could add some baseboard heaters also.

 

[DonTee]

So we’re thinking 24k btu is the size I should look for?

 

[EbS-P]

So we’re thinking 24k btu is the size I should look for?

If looking at the mr cool diy the output at 5F is probably 15k btu. That works out to about 3 pounds of firewood an hour (at 20 % MC burned at about 65% efficiency). So if you burn 70 pounds of wood or less on a really cold day it would keep up. It appears to me the minimum heat output is only different by 1000btus between the the 18 and 24. So Id with the the 24.

I get the whole don’t over size for cooling but these units the turn down is low enough and the fact you can run a programable thermostat where you can set it colder for a couple hours and knock the humidity down. And theoretically they have the humidity control mode that runs the cool below the indoor dew point problem is it just doesn’t move enough air to keep the humidity low. If it did the house would might get too cold. Bummer a cold dry house on the hottest most humid summer days.

18k btu runs on #12 wire I think. The 24 probably needs #10 but I didn’t read close enough to be sure. I have not looked at the price of wire in a while.

I can easily burn 70# of wood a day in my 1.6 cu ft stove and I have a 36k btu heatpump that does 22k at 32 dF. My point is if it’s pipe freezing cold and you are not there have another plan like heat wrap, or a baseboard heater.

Just some thoughts. I haven’t actually bought a mr cool unit. Have been close a couple times. Got a second wood stove last year instead. Could never justify the extra cost of a name brand or the install since I have heatpump that does ok already.

 

[gthomas785]

So we’re thinking 24k btu is the size I should look for?

Do a manual J on your house to figure out heating and cooling loads. Don't guess.
www.loadcalc.net

 

[DonTee]

Ok thanks. I’ll check it out.

 

[EbS-P]

I’ve never actually completed a manual j though I have started it at least 5 times. It’s a good idea but I’m guessing at some of values I’m putting in.

Any way. Learn from others mistakes. Don’t snap off the line set.

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[gthomas785]

For the manual J I usually recommend people look at the spreadsheet, then make a list of all the measurements you need to do and then walk around with your tape measure. It's definitely not a project you can finish in 10 mins. Each window and door gets a number to make things clearer.

There's a ton of good refrigeration / HVAC content on YouTube, however look for the professional channels not the diy guy doing it for his first time. There's lots of misinformation/bad advice out there as well.

 

[DonTee]

Yeah I glanced at it and it’s a little confusing. If I could find a guide on how to fill it out that would be nice. Or I could look at a completed sheet like you said.
I have 18 windows in my house, but they’re all one of two sizes.

 

[EbS-P]

Quick search finds this.

Downloads - Public Files - ACCA

View the selected document's details

www.acca.org

 

[EbS-P]

Quick search finds this.

Downloads - Public Files - ACCA

View the selected document's details

www.acca.org

The issue you have is a nonstandard Indoor temp. Say 55dF. I’m not sure I’d that is allowed in the manual j sheet I just posted. Hence my how much wood do you burn estimate.

 

[DonTee]

Ah gotcha. I don’t have good numbers for that. I haven’t consistently stayed in this house all winter since we built it. Last winter was the first, and we were only here for part of the winter. It’s been seasonal until this point.
And, I’ve changed woodstoves. I started out with an old Timberline stove until last year. Then I had a VC encore for most of the winter. And this year I’ll have a BK Princess.

Last winter I burned almost 4 cords. But that was with the house under insulated. This winter it will be fully insulated, with a vapor barrier, drywall, and the BK stove.

 

[coaly]

I installed my first mini-split in a rental home last year. Used as the primary heat with a propane stove back up that has not been needed.

Not difficult, but I was a propane appliance and heat tech (no heat pump or mini splits back then) for many years with my own service business. The only thing different was torquing copper flare fittings and using Nylog Blue lubricant/sealer on fittings that are normally done dry.
Many like mine are 220 volt that have a DC inverter to run very efficient DC motors. 12-2 wiring in most cases uses 220v breaker, and both conductors were 110v hot, with no neutral needed. Disconnect at outside unit, connecting harness from outside to inside unit supplied.

Like many, my outside unit was precharged for diy installation. You will need a vacuum pump with gauges to vacuum the system, confirm it holds vacuum and slowly open valves on outside unit allowing the precharged refrigerant into system. Once you do it following installation instructions, it’s not that difficult.

I had a professional precision flaring tool, so I could cut and flare tubing. If you don’t have a good one, you need to use the factory flares making sure they are perfect. The line set connects at both inside and outside units with flare fittings.

So special tools required would be a vacuum pump and gauge set, means of torquing fittings, precision flare tool if you need to shorten line set. And Nylog Blue Gasket and Thread Sealant. Practice on many flares if you are not well versed in copper tubing flaring. You will also need line set covers for outside to run lines through before connecting. I’ve had very good experiences with Pioneer brand as well.

 

[Highbeam]

If you go over on lineset length then you’ll need a pro to add refrigerant. I’m finding most come charged with only enough for 25’.

The mr cool diy kits allow you to add more length without adding refrigerant.

 

[DonTee]

Thanks for the detailed write up coaly. I either have or can borrow the tools I need. I’ll need to get some of the thread sealant.

I haven’t decided (my wife hasn’t told me. Lol) where the mini split is going. It would be nice to keep the run from inside to outside at 25’ or under. I imagine she would want the outside unit on the back of the house. But maybe it could go on the side by the electric panel. That would be easy since my outside panel has spaces for breakers as well.
I know I have some 30 amp 220 breakers left. Maybe I have a 20 amp as well. I know when I was wiring the house I had issues finding some breaker sizes. Seems the Eaton BR series are hard to find because of the covid shortages.