Thoughts on mini-split versus central HVAC systems

[Steve Rozmiarek]

Don't underestimate the filter issue. I have two conventional furnaces doing exactly what you were thinking in your shop in mine. My shop is surprisingly low on dust, but I still have to change filters very often, like weekly when I'm working in there heavily. Easy and cheap to do with a conventional furnace. The mini splits that get installed in our projects are far less user friendly to deal with filters. The head units on the LG, Lennox and Fuji units that our HVAC guys use are also quite a lot more sensitive to dust.

I need better heating capabilities in that space too, I know a mini split wouldn't keep up. They make excellent air conditioners but less so heaters. If it was my quandary, I'd consider moving one of the functional ducted units you are thinking of upgrading in your house to your shop.

[Jack Frederick]

Steve, for supplemental heating or stand alone heating try the Rinnai Direct Vent Wall Furnaces. They are excellent. Pricey, but a great feature set and beside running a gas line they are about a two hr install. Vent is included as is the programmable stat.

[Tom M King]

By the time I recovered the refrigerant out of the system, it was too hot in the attic to fiddle with the tubing this morning. It will probably be day after tomorrow before I get to it. I need to get caught up on cutting grass.

They had put almost a whole pound too much refrigerant in the system. First check on the new recovery tank shows it's not contaminated comparing temperature to pressure. I left it in a cool place, and will check it again first thing in the morning at a lower temperature. If it still looks good in the morning, I'll just reuse it in that system after I fix the tubing, and pressure test it.

[Steve Mathews]

Don't underestimate the filter issue. I have two conventional furnaces doing exactly what you were thinking in your shop in mine. My shop is surprisingly low on dust, but I still have to change filters very often, like weekly when I'm working in there heavily. Easy and cheap to do with a conventional furnace. The mini splits that get installed in our projects are far less user friendly to deal with filters. The head units on the LG, Lennox and Fuji units that our HVAC guys use are also quite a lot more sensitive to dust.

I need better heating capabilities in that space too, I know a mini split wouldn't keep up. They make excellent air conditioners but less so heaters. If it was my quandary, I'd consider moving one of the functional ducted units you are thinking of upgrading in your house to your shop.

I was thinking the same thing last night. The oldest unit in the house might be a prime candidate to relocated to the shop.

[Andrew More]

I understand the OP said the insulation needed to be addressed, but I still feel it hasn't been given it's proper due. I find with mine that I can get up to a 10 deg temp differential WITHOUT doing anything else. Also it will even out the temps through the day, which resolves a lot of comfort issues. If the weather is already generally comfortable enough I would strongly advise that the insulation be installed, and the situation re-evaluated after this occurs. Generally speaking this can be done in a day or two of work, at which point the OP will have a much better idea of their situation.

That having been said, I've got a nice fujisui minisplit that a friend helped me install. I agree with Jim that I cannot find the power draw on my bills. However I also caulked, sealed, and insulated (over insulated) the garage massively before this happened.

[John Pariseau]

I understand the OP said the insulation needed to be addressed, but I still feel it hasn't been given it's proper due. I find with mine that I can get up to a 10 deg temp differential WITHOUT doing anything else. Also it will even out the temps through the day, which resolves a lot of comfort issues. If the weather is already generally comfortable enough I would strongly advise that the insulation be installed

Second this. And not just insulation but air sealing. I don't have data before insulation, but the attached chart shows the temperature/humidity swings over the past few days (we lost power and I'm missing data from a few days back, hence why my humidity spikes at the beginning). I also have data saved since I installed my network over there (two years?), but essentially:

• Humidity (before dehumidifier) was always around 60% - I keep the unit set to 55% and it holds it pretty steady
• Temperature is always cooler than the peaks during the summer, and warmer than the peaks during the winter - anywhere from 5-15 degrees, sometimes more in the winter
• Some summer days it can be oppressive, that's typically a function of humidity inside vs outside - most of the time even at 74 degrees it's comfortable to work in with just a fan going

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[Ole Anderson]

To my understanding, mini-splits run with a variable speed compressor and fan using inverter technology whereas traditional units are either on or off. Traditional units are available with variable speed inverter technology, but are quite expensive.

[Tom Bender]

John
That's pretty impressive performance. You must have sealed it up real tight to hold humidity so close. Can you share some details, and maybe a picture of the barn?

[mark mcfarlane]

I have a few minisplt systems and a 2-stage conventional HVAC system. One large Mitsubishi mini-split in the garage, heats and cools 1000 sq feet. Sips electricity (open cell foamed walls and attic). Throws the cool air just fine across 35'. The other mini split is a multi-headed 'cassette in celling' unit - separate HVAC heads in each room, no ducts.

The Mitsubishi in the shop can run from 10%-100%, continuously adjustable. One of the big benefits is that it can very efficiently remove humidity from my shop year-round, whilst trickling electricity. Nice feature when there is a bunch of exposed iron in the shop.

Traditional HVAC system, even the two stage ones, aren't nearly as good at removing humidity in the spring and fall in Houston when they only kick on for 10-15 minutes at a time. I have read it takes 10-15 minutes for the first drips (captured humidity) to come out a traditional HVAC system. If the system only runs 10 minutes the condensate stays in the pan and gets redistributed into the home.

I'm a huge fan of mini-splits.

Regarding cleanliness, I only have to clean my shop mini-split filter 2 times a year. end even then it is not very dirty. This is likely because I have two air cleaners that I run when making dust, and my DC system is very good, so very little dust gets to the mini split, or my lungs.

[John Lifer]

One point that has not been made with mini splits is that they can HEAT efficiently down to well below zero. I installed a Senville last year myself, and the only hard part was drilling a 3 inch hole through my cast concrete basement wall. Once that was done, I cast a 3x4ft pad (didn't want to buy a pad that would have to have been leveled anyway due to slope) then installed the base bolting it down. I left the lines full length and they ended up perfect for my install. I didn't purge with nitrogen, but did buy a vacuum pump and pumped out the lines and inside unit (gas is inside the exterior unit full charge with set line length). Opened up the lines and then checked pressure with my gauges. Was perfectly at right pressure. Unit was really purchased to heat basement as basement was not built with intention of really heating with the main HVAC, only a couple of drops unfortunately. But it works well. EASY install, tools were a few $ off amazon.

[Timothy Orr]

FYI if you are thinking of adding A/C a couple things to be aware of:

On Jan 1, 2023, new efficiency regulations go into effect which most certainly will result in higher unit costs for the lowest efficiency units.

By 2025, manufacturers have to switch from the current refrigerant (R-410a) to new lower global warming potential refrigerants, which again most likely will add cost.

However the recently passed Inflation Reduction Act extended the section 25C tax credits for high efficiency systems for 2022, expanded the tax credits in future years and added a significant (up to $8k) rebate for very high efficiency heat pumps starting next year. The rebate program is not fully defined yet, but will be state administered and the amount available will depend on your income relative to your place of residence.

Just some things to think about if you are in the market for a system

[Rich Konopka]

I just had 2 mini splits installed if my soon to be dream workshop. I chose Mitsubitsi units because they have a dry mode which works well for the humidity we experience in Atlanta. They are whisperer quiet if that matters in a noisy workshop.

[Maurice Mcmurry]

Mitsubishi is doing a great job making air conditioners!

[Tom M King]

For those installing mini splits themselves, I've heard of more than a few people having trouble with the flare fittings leaking, including the pro that installed one for us. I've never known anyone who uses these to have a leak: https://www.amazon.com/dp/B07M81FBF9...v_ov_lig_dp_it

I use flare nut sockets and a torque wrench to eliminate guesswork too. I don't want to be one leaking refrigerant into that atmosphere, so I also pressure test with Nitrogen before even thinking about charging with refrigerant.

I bought this pressure regulator, and a 40 Cu. Ft. tank from a local AirGas place. The tank filled with Nitrogen was 140, and less than 25 dollars for a refill.
I read too many bad reviews on the cheap Chinese regulators. This one works really easily, and nicely:
https://www.supplyhouse.com/Turbo-To...tor-0-800-PSIG

That's a very good supplier for all things HVAC. I have a pro account there, so get a discount and free shipping on any order. Orders come next day, or second day.

[Maurice Mcmurry]

+1 for Tom M Kings techniques and tools! Using AC flair fitting compound is important. The little single use catsup packets of compound that come with some brands are difficult to use. I keep a bottle with a precise applicator tip. It's nice that many tools for air conditioning are still made in the USA.