Mini split installation for a house

[Zachary Hoyt]

I've been waiting for months for someone who is supposedly going to install a mini split, and today when he returned my last call he said that he would be getting a quote to me soon, but it would be higher than the $2-3k range he had guessed at an earlier time. He doesn't design the systems, just installs them. I'm thinking more seriously about doing it myself instead. The plan is to install it on the ground floor, which is open, 15' wide and 31 feet long for the kitchen and living room. There is also an added guest bedroom on one side but I am not worried about that for now. The whole house has closed cell spray foam now that the addition got done, so we're pretty well sealed.

We are planning to use a mini split for heat in spring and fall, but when the temperature outside goes below freezing we'll use the wood stove, which is working fine and seems like it would be able to heat the whole house even in cold spells. So far we've only had to have a fire a few hours a day, even with lows in the mid 20s. The mini split would have to be able to survive to -40 but we wouldn't be using it when it's cold. I'm looking at some kits that say they are DIY, like Mr Cool, which I have heard folks on here speak highly of. I'm also wondering how hard it would be for a non-HVAC person like me to buy or rent a vacuum pump and learn to do the lines myself. It seems like there are a lot more mini-split options if I was able to do that. I'll be grateful for any advice.

[Kris Cook]

I bought two units a couple of years ago and kept putting off professional installation until I had them both ready to fire up. I wanted to take advantage of a professional install to maintain the 7 year warranty. I realized I was already 2 years into the warranty period with no benefit of the units. Bit the bullet earlier this summer and installed the one in the shop by myself. It was pretty easy. If you are looking at a single-zone system then it is pretty straight-forward. I don't know anything about multiple-zone systems but can't imagine it would be that complicated. The units I purchased are Daikin they came pre-charged and I believe the charge is good up to about 25 ft. of line set if I remember correctly. If going beyond the pre-charged length you would have to add refrigerant which complicates things, I believe.

Anyway, I got the pump and gages for less than $200 (the same set is not $146 on Amazon). I also bought an eccentric flaring tool and a set of crow's feet so I could use my standard torque wrench. I can share the components if you are interested.

There are others on here with more experience and hopefully they will chime in.

[Zachary Hoyt]

Thank you, that's great to know that it worked for you. Good for you for getting it done. The deeper I dig into this the more I'm confused about which "DIY" kits require a pump and such, and how to tell them from the ones that don't.

[Tom M King]

You need a vacuum pump to evacuate the lines, I expect even with the precharged units, but I have no experience with them, so really don't know.

The system operates under high pressure, so the flare fittings are critical. Even pros have trouble with them leaking. Use these: https://www.amazon.com/dp/B07M81FBF9...v_ov_lig_dp_it

and torque the fittings properly with a flare nut crows foot on a torque wrench.

Even with a vacuum pump to evacuate the system, and a pressure gauge to see if it's holding vacuum, I still don't want to put refrigerant in a system without pressure testing it first with Nitrogen. No refrigerant should be released into the atmosphere, and guesswork has a high probability of that as a result.

It takes a grand or two to get set up good to work on HVAC systems, and you can easily spend way more.

I do business with, and recommend: Supplyhouse.com and Trutechtools.com

[Bill George]

As a guy who worked in the commercial HVAC/R field and then after being retired for a few years and installed my own Mini Split HP. My son who is still in the business recommends Mitsubishi as that is what his commercial Co used and had next to zero issues. Made in Japan all mini splits are not the same quality.

#1 Buy a good flaring tool, I used Rol Aire as I used for many, many years to make a leakproof flare on the first try and they make the flare with a segmented flaring cone above the flaring bar and then also polishes it, the tool is expensive!

#2 Since the flares are subject to cold and hot use either Leak Lock or Blue Loctite behind the flare nut and on the threads... it stops the loosing of the flare.

#3 Use a torque wrench, I never did but I have been doing this for over 30 years.

#4. Leak check first with either dry nitrogen or refrigerant that does not require recovery, I used a tank of R134a for pressure. Think, if you pull a vacuum before pressure checking, your just sucking in air and moisture in from any leak. Vacuum leak checking is only at 14.7 psig, think why?

#5 Use a good vacuum pump to pull down to at least 500 microns.

#6 Open those service valves slowly and you do have gauges for R410a? Recheck those fittings again.

#7 I did have a minor leak on the liquid line I needed to repair, but all is fine now. Works down to say -12 or so heating very low energy costs! This is going to be my 4th heating season.

[Maurice Mcmurry]

If you can make stock line sets work you can skip DIY flaring and avoid potential problems. Pioneer caters to DIY but there is a "Certified Installer" line on the warrantee form. Pulling a vacuum can also be bypassed with a line flushing kit. I think a deep vacuum that holds for a day or two is the best leak test.

[Jim Becker]

Mr Cool DIY systems can be installed without a vacuum pump as the line-sets are pre charged. The current range is broad and multi-air handler units are available which is typically what you want for a home. I'll be using one of these units in my new shop building, but likely with just a single air handler since it's an open space. (Buying mine through Costco)

Do note that many mini splits available today can handle outside temps down to as much as -5º F. Check the specifications if that's important to you.

[Zachary Hoyt]

Thank you all for the advice. Jim Becker, I think that the house here is more analogous to a typical workshop in some ways, since it's an open rectangular area that we want to heat and cool, and the bedrooms can take care of themselves at least for now. It's not important to me to be able to use a mini-split at -5, as I imagine the stove will keep up with that if we keep it stoked steadily, but I haven't found much information about what temps the outside unit can withstand without a problem, and it can get pretty cold here at times.

[Ronald Blue]

I put two Mr Cool mini splits in my shop this summer. Home Depot was the best price and almost immediate availability. I think they were in store in three days. Mine weren't DIY as far as the lines weren't pre-charged. I had my local HVAC guy assist and when we were finished it was about $500 for his labor. He recommended Mr Cool. The price is definitely competitive. Ther were $1,100+ each. They worked great as cooling units. I have radiant floor heat for cold weather. They also have ducted mini splits as I understand it. I can look at the manual and see what temperature range it lists.

[Bill George]

For a system that runs 400 plus psig on the high side, leak testing should be done at pressures 300 psig or more. Dry nitrogen is best because it is stable temperature wise and much cheaper and legal compared to refrigerant.

Removing all the air and then down into a deep vacuum means you pressure checked at 15 (14.7) psig Which is better?


BTW my Mitsubishi Hi HP works and heats down to -12 and the compressor, outside and inside fan motors all modulate speeds according to the load.

[Tom M King]

There are cheap nitrogen regulators, but I bought a good one. Buying a filled 40 cu. ft. tank cost $140. Refilling it costs a few cents less than $25. Now that I own the rig, I can pressure test as much as I want to, and purge the inside of the lines if I want to braze. Total rig cost cheaper than one service call around here.

This is the regulator I bought, and it works like a charm. You can buy cheaper ones, but the reviews don't sound so great.

https://www.trutechtools.com/victor-...r-cga-580.html

[Jim Becker]

Thank you all for the advice. Jim Becker, I think that the house here is more analogous to a typical workshop in some ways, since it's an open rectangular area that we want to heat and cool, and the bedrooms can take care of themselves at least for now. It's not important to me to be able to use a mini-split at -5, as I imagine the stove will keep up with that if we keep it stoked steadily, but I haven't found much information about what temps the outside unit can withstand without a problem, and it can get pretty cold here at times.

I think you'll be pleased with the performance. The temperature floor should be in a unit's specifications, but having the woodstove is certainly a boon for when things are blowin' up there in the sticks. With the house being somewhat open as you describe, the simpler units should work fine. A 24K BTU unit covers up to about 1000 square feet, and with good insulation and infiltration sealing, things can be pretty comfortable. If you are doing through-floor vents so your woodstove heat can circulate upstairs, you will likely get similar benefit with the split when using it. Going with the mini split also gives you AC, so that's a win-win, IMHO. You may not need it as often as farther south, but it will cover "those times" when things get sticky and that's unfortunately very likely to be more frequently going into the future.

[Bill George]

Just about any Nitrogen regulator would work fine.

I did some reading on the Mr. Cool units seem like a decent HP but it looks like they are Made in China so time will tell.

One issue is the pre-charged line sets, my experience in running service years ago when the DIY AC units were sold at home improvement stores, the homeowner would install and screw up the install and they leaked. So we were called by the irate homeowner who did not understand since he screwed it up, he had to pay! The Warranty did not cover either, and we did not get paid. That was the end of doing DIY service calls for homeowners.

My personal opinion, flare fittings have no business on high pressure R-410a, we either silver brazed or Sil Phos brazed those fittings. with Nitrogen purge to prevent the copper oxide scale from forming on the inside.

There is now in the future a phase out of R410a and the replacement is flammable.

Try buying R410a to top off your unit when its been leaking.

[Jack Frederick]

I use Fujitsu minis. I was the factory rep in the six New England States for 14 yrs and saw, well, a lot. The vast majority f mini problems are poor flares. In heat mode you are pushing 6-800 psi and it is in heat that problems show. Absolutely use the nitrogen purge. It will show your flare issues if there are any and you want to be absolutely certain they are right before you release the refrigerant. When making up the flares wipe a finger wetted with your vac pump oil on the face of the flare. Just moisten it a bit. I had people send units back to Fujitsu and if there was leak lock or any type of dope on the threads they would refuse warranty out of hand. I would never use factory flares on a line set. Line set manuf could care less of a system leaks. They flare the lines only to hold the plastic shipping plug in place. I use a Hillmar flaring tool. I have the Yellow Jacket unit but found a couple leaks with it as the 1/4” tubing slipped. Cut a few feet of line set and practice flaring it until you are comfortable. DO NOT put the condensing unit on a pad outside. Having grown up Upstate as I recall it gets cold and actually snows. It is disappointing when the condensing unit turns into an ice cube. Either use one of the wall mount kits or a high standoff on the pad. I have seen frost heave about turn these things over, so… Set it level and keep it there. Elevating keeps it clean as well. Should you be tempted to braze the line sets use the nitrogen or you will sugar that line set. Also it doesn’t take a lot to plug a 1/4” tube. Mitsu and Fujitsu are one/two in the US. I won’t touch a Daikin as they pissed me off back in ‘84. Living in Orwell i would only go for the low temp units. You need to research the lines you are interested in and make sure you understand the specs on each model within a manuf line up. it is complicated so make sure you understand what you are buying. Oh, and the drain. I find it really difficult to close the unit onto the mounting bracket with the power line, insulated line set and the flexible drain. it is the classic 5# in a 4# bag. Most manuf I believe let you move the drain connection to the left side. You can then run it directly. Trap moisture in a humid climate, yours, and you cannot believe how fast mold will grow.
If you are looking for a heating alternative I would suggest a Rinnai EX-22 LP or NG. Not inexpensive, but excellent. I introduced those in New England in ‘91 and have heated my homes, shop, garages and basement with them since. I’m sitting about 8’ from one now. The minis are on the other side of the house and upstairs. They are an excellent companion to minis, a simple install and bullet proof.

[Bill George]

Jack I agree 100% Except for the blue Locktite on the threads only, Never any on the flare face. Having worked commercial refrigeration service for years I always found the leaks on TEV flare nuts in the cooler case or WI cooler, a little on those threads, (expansion and contraction) Never on the flare face and we did not have call backs. Those flared line sets were fine for R22 but really should be redone as you describe for the high pressure R410a.