Pondering a mini-split AC

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Forum topic by farmfromkansas posted 07-22-2019 01:11 PM 679 views 0 times favorited 7 replies Add to Favorites Watch
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220 posts in 631 days

07-22-2019 01:11 PM

Was looking at info on sites about mini-split systems, and find Pioneer recommended on a HVAC website, they say the difference between DIY and regular systems is that the lines are pre- vacuumed on the DIY. Suppose you could cut the lines to length if you go with the regular system, as they use compression fittings, but you have to vacuum the lines. The units are still pre- charged with refrigerant, so really not that big a deal considering the up charge for the DIY units. Anyone have any recommendations for brand? Mitsubishi is priced out of the competition being multiples higher priced. Second, my shop is a little bigger than average, and is 25×50 inside, so looking at 1250 square feet, besides having a 17×25 store room with the DC, air compressor, lumber storage, and tire machine. There is an open door way between the two rooms. Assuming I would need a 2 1/2 ton ac, or maybe just get the 2 ton, and it will run constantly on hot days.

7 replies so far

View dbw's profile


519 posts in 2653 days

#1 posted 07-23-2019 05:42 PM

One of these days I’m going to get a mini-split for my garage. I have done some research and I have come to the conclusion this type of work is best performed by someone who knows how to. For me I could either spend countless hours messing with something about which I know very little (and potentially have a poor outcome) or I could hire a professional HVAC company and have it done correctly, fast, and, should there be a problem, have a number to call.

-- Woodworking is like a vicious cycle. The more tools you buy the more you find to buy.

View EarlS's profile


4315 posts in 3365 days

#2 posted 07-23-2019 06:08 PM

I’m going with a professional installation since I know very little about what systems are good and how to properly install them. The local HVAC rep recommended an Ameristar Ductless Heat Pump – 12,000 BTU/hr for my 13×20 shop.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View farmfromkansas's profile


220 posts in 631 days

#3 posted 07-24-2019 02:10 AM

I have a friend who is a retired HVAC guy. He installed the furnace and AC in my house, as well as the existing stuff in the shop. Just thinking the high efficiency of the mini split systems may make my shop cooling affordable, and I can do most of the work, he said he will show me how to use the vacuum pump and connect the unit.

View YesHaveSome's profile


189 posts in 1275 days

#4 posted 07-24-2019 01:16 PM

I installed a Pioneer myself last year. I paid an HVAC tech $150 to vacuum the lines and do final connections. He also came to the house before I started just to walk through installation. It was easy.

If you’re going to cut the lines it makes no sense to get something like a Mr Cool. That’s the only difference between those and other brands (installation-wise).

-- But where does the meat go?

View clin's profile


1128 posts in 2013 days

#5 posted 07-24-2019 07:33 PM

Mini-splits are great. I use one in my shop. 2 tons of AC is almost certainly too much for a 1250 sq-ft shop. Though I wasn’t 100% sure how this storage room figured into what you wanted to heat and cool. Even if this is added in at for a total of 1,675 sq-ft, 2 tons is probably more than you need.

Using square footage to estimate HVAC is close to useless. Heat load, has some relationship to square footage, due to the roof/ceiling area. But walls and windows matter a lot.

How the space is constructed, how much exterior wall area there is. Window size and location. Size of eaves and overhangs, if any. Type of roof and attic. And of course your local climate makes a huge difference in what your needs are.

Almost universally an HVAC installer will quote an oversized unit. Not because they are trying to trick you, but becasue they either don’t know how or don’t want to take the time to figure out what you really need. They don’t get callbacks on oversized systems. The fact you paid more for a larger system, that it runs less efficiently (costing you more in electricity), and perhaps is not as comfortable as it could be. These are all things that won’t cause a callback. So they have no reason to worry about over-sizing.

The above is based on how you cool a typical space. On the other hand, if you want to leave the space unconditioned through the week, then walk in Saturday afternoon and have the shop cooled in minutes, then bigger is better. And probably not a mini-split.

Mini-splits are extremely efficient, but they are like a car on the highway. Keep them cruising at a constant speed and they sip electricity. This is why they would typically be running 24/7. Or if you’re a weekend warrior, perhaps turn it on Friday night or early Saturday morning, to have everything perfect later.

Mine, I just turn the thermostat back for the days I know I won’t be in there. That way the shop never gets super hot, or cold in the winter. And that’s good for the glues and paints stored in there anyway.

Unless you do the calculations, you’re guessing. The “official” way of doing this is to run a “Manual-J” calculation. This is based on the ACCA Manual J for residential heating and cooling load calculations.

It’s fundamentally easy to do, but the manual is an inch thick and full of tables to cover all the different construction methods, insulation types and amounts, types of windows, even color of the roof factors in. The ACCA provides a nice Excel spread sheet to fill out, but without the tables and the information on how to use them, they’re of no value.

There’s even software you can get. One program I used was HVAC-calc:

For a one-off job you can buy a license for $49 good for 2-months. It is based on Manual J, but is easier to use and you don’t need to know all the Manual J stuff to use it. I know it seems like an unnecessary expense, but you’re looking at spending maybe a few thousand dollars, so $49 to make sure you get the correct unit is money well spent. Might even save you outright if you need a smaller and less expensive unit. Plus they have a demo you can check out. So no harm in looking at it.

As always, first step is to insulate the shop if not already.

I also agree that they are relatively easy to install. I did NOT do my own because it was part of a larger installation of a total of three units. But it still took 2 guys about two days to do that. And that was me providing the electrical connection. But every install is different. Most complex thing is running the drain line for the condensation. But even that is trivial if the head (inside part) is mounted on an exterior wall.

Anyway, mini-splits are great. I’m sure you’ll love it.

-- Clin

View BoilerUp21's profile


167 posts in 1784 days

#6 posted 07-24-2019 08:08 PM

I just purchased the Advantage 3rd Gen 18,000 BTU 1.5 Ton Ductless Mini Split Air Conditioner and Heat Pump 230-Volt/60Hz – White. I posted this a couple days ago, and they actually sent me a 17% off coupon and refunded me the difference…Supposed to get delivered tomorrow and I will start the install process…

If anyone is looking for something similar, there is a great price on for this unit with a 14% off coupon today…
This coupon along with purchasing $750 worth of their online gift cards from @ a 3.5% discount for $713.75 gets the system shipped to your door for $787.66 out of pocket after tax.
The unit has a 19 SEER rating and is Wifi enabled so you can control remotely. I will have to have an electrician hook up the additional 220v line i am running and HVAC tech to charge the system.
Just thought i would share if anyone else was in the same boat.

View soob's profile


271 posts in 2225 days

#7 posted 07-24-2019 08:13 PM

The “diy” mini splits are a gimmick and inferior because you end up with a coiled up line (and associated efficiency penalties) you can’t shorten. And a vacuum pump costs less than the markup.

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