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Thread: Thoughts on mini-split versus central HVAC systems

  1. #1

    Thoughts on mini-split versus central HVAC systems

    While obtaining a rough cost on a mini-split installation for my shop I asked a couple of local contractors what a similar capacity central HVAC system would cost. I was surprised to learn that the latter without ductwork would be about the same and possibly a little cheaper. Then I thought why not place the central air handler on the portion of a recently constructed mezzanine where the the slope of the roof makes the area almost useless. The intake could be provided with necessary filters with little ductwork and exhaust into the open space of the shop, again with little ductwork. The compressor unit would be immediately outside along the same exterior wall. See pic below. The advantages that I can see with this setup as opposed to a mini-split is 1) a propane furnace could be used instead of the heat pump, which will probably heat up the space faster. 2) better air filtration 3) used systems are readily available at a fraction of the cost. I'm not too concerned about the not so ideal efficiency of a used system. I would only use the system for heating and cooling a few weeks out of the year. Most of the time it's quite comfortable in the shop with our southwest climate. And yes, before it's mentioned, I need to address the lack of insulation.
    shop 003.jpg

  2. #2
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    A good mini split will be much more efficient and quieter, inside and out. Can you get a whole house unit small enough in BTUs?
    Climate? Humid climates want the ac to run on low for hours to dry out the air. Not possible with a too big system. Not a issue here just repeating what I have heard. In my climate I oversize the system and never run it above low speed to keep it quiet.
    Freidrich is the quietest system. Some units are more then double the lowest noise. DB sound is a log scale so 7 DB more is double the noise.
    Bill D

  3. #3
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    A disadvantage of a mini split is the small thin air filter. In a shop it will need to be cleaned very often. A ducted air handler can have a big thick pleated filter.
    Best Regards, Maurice

  4. #4
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    If the cost were the same, the MiniSpilt is a huge winner when it comes to efficiency and cost to operate...so efficient, there's almost no reason to turn it off when you're not in the shop so "warm up" or "cool down" time is almost nil. Even if you do shut it off, it gets to temp pretty quickly, in my experience. And you can also easily install your own with a DIY system such as from Mr Cool that doesn't even require doing the vacuum dance on the lines. 24K BTU will cost you about $25-2800.

    That said, insulation is your friend so be sure to consider that.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  5. #5
    Quote Originally Posted by Jim Becker View Post
    If the cost were the same, the MiniSpilt is a huge winner when it comes to efficiency and cost to operate...so efficient, there's almost no reason to turn it off when you're not in the shop so "warm up" or "cool down" time is almost nil. Even if you do shut it off, it gets to temp pretty quickly, in my experience. And you can also easily install your own with a DIY system such as from Mr Cool that doesn't even require doing the vacuum dance on the lines. 24K BTU will cost you about $25-2800.

    That said, insulation is your friend so be sure to consider that.
    Efficiency and the noise factor are both important considerations but I would have to be convinced that the mini-split systems offer that advantage. I'm not saying they don't, I just don't know. It seems to me both systems both have fans to move air and both have a compressor for the AC/heat pump. What makes the mini-split perform better with these functions? I've also learned that most if not all mini-split systems are made outside the US while traditional central systems are made in the US. I consider it a plus to have something made in the US. I'm also attracted to the idea of purchasing something used and there seems to be quite a few of the central systems available cheap.

  6. #6
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    Let's just say that when I put the minisplit in my old shop in 2018 and left it running pretty much year-round from then until we moved in 2021, the electric bill barely reflected it. That's why I'm going to do it again with the new shop building, although it will be a slightly larger unit since the shop will also be bigger. That said, my previous shop was insulated before the unit went in. The new shop will also be insulated. There's a reason that all the name brand HVAC companies are moving to the same inverter technology for their higher end systems that first surfaced in the mini split world and that's efficiency leadership.

    I cannot argue that most mini splits, regardless of brand, are made outside of North America. After all, they were a lot more popular "over there" before hitting our shores for residential use.

    That all said, there's no harm in picking up a used HVAC system if one of the correct size is available and is in good condition. Be careful about going too old, however, as older systems are getting harder and harder to maintain based on comments from a friend who's in the business.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #7
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    If you buy a used system, make sure it's new enough to run R410a, and not R22. I bought a used 6 ton gas pack (gas furnace with AC) for $500 that was only four years old, and used in a building that wasn't used much. I haven't done anything with it yet, but was too good of a deal to let pass. An HVAC guy had it on his trailer, and didn't have a way to unload it. He took it off of a building that was being torn down, and they loaded it for him. It's pretty heavy, but I have a loader. I do have shops to put it in, but the to-do list is not getting shorter.

    We put an 18k btu Mini Split in a suite that I converted other space in our house for my 106 year old Mother. Long story short, it does go good that we cooled about 7,000 sq. ft. of super insulated house with it, and a couple of fans running. Our Summer bills were over $200 a month cheaper through the Summer that before that little mini split. We did have to run one other heat pump when temps were above 97, but that was just for a few days this Summer.

    Long story short, I'm impressed with the mini split.

  8. #8
    Can't argue with the positive mini-split experiences. Insulation needs to be addressed first before committing to either systems.

  9. #9
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    I don't think there's much difference between a ducted mini-split and a small air conditioner as the components are essentially the same. The highest efficiency is obtained with a ductless mini-split as there is no energy wasted running air through ducts. A mini-split or regular AC in a shop won't be quite as efficient once you start adding filters into the mix but for the amount of time most hobbyists spend in the shop it's likely not significant. Adding a decent filter might be easier with a system designed to be ducted in the first place as they assume the static pressure will be higher.

    A modern heat pump will be more efficient for heating and there are sometimes government incentives available for switching from gas to electric heat pump.

  10. #10
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    I don’t know how large your space is, but as you say you are in the SW I will assume a pretty moderate heating climate. You could certainly go with a conventional US made system, but the fact is, you will be outfitting a new building with older type less efficient equipment. Check the seer ratings on the mini-splits vs what you are buying. You will likely be in the mid-20’s with a ms and maybe mid teens with the central. As to propane, I was in the business all my working life and am a member of private oil and gas groups and the owner of one of those groups just posted that fuel inventories are all ready low and we will likely see much higher prices this winter. Thank Vlad the Impaler for that. I represented Fujitsu for 14 yrs in the six New England States. When we introduced the inverter 410a equipment it was simply amazing the difference in operational efficiency. We at least doubled the numbers of the unitary gear. Back in the early ‘00’s the US manuf were being forced to go from a 10 seer to a 13 seer. They fought it and fought it, tooth and nail, but finally complied, then doing everything they could to get around it. All the while they were aware of what was coming from Asia and they did not a damned thing to invest and develop. Instead they lobbied and fought through regulation so they could continue to make central less efficient gear. Today, they are getting rolled over and they deserve it. Mini’s are more efficient and they are quieter. Go to the Fujitsu site and download their catalog for comparison. The other reason to go mini’s is that you can spend some dough and put solar on your shop. I did it and have zeroed my elec bill and at PG&E rates, that is real money. I installed my own system. If you want info on taht pm me and I can advise. Anything fossil fuel cannot do that and youy will continue to pay the man. Minis are the best bet in technology today in the HVAC world, Yes, you absolutely have to pay attention to your filter service and know how to remove the cover for service. Oh, another thing, one of the reasons they are quieter is that they have segmented, small diameter blowers that are offset section to section. Conventional furnace and air handler blowers are large diameter and they tend to shop the air rather than slice the air. Much quieter. As you can see, I can go on and on, but bite the bullet and put in the mini-split of your choice. You will be happy you did .

  11. #11
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    I am a major mini-split fan boy but I see some sense in the OP's thinking. A plug in whole house electrostatic filter and a humidifier would be incredibly easy to plumb into a whole house unit. He could go all sorts of different ways for air filtering with the whole house unit. I will never go back to a whole house AC but I see some sense in what the OP is saying.

    I would also guess that a whole house unit would have a more powerful blower than a mini split which might be useful for air filtering.
    Last edited by Michael Schuch; 08-29-2022 at 4:05 AM.

  12. #12
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    The minisplit indoor head is not magic. It is just a coil and fan with some wiring with a drain trough for condensation. No reason it could not be taken apart and put into a tin box with regular size, easy to change, filters on the air intake side.
    Bill D

  13. #13
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    Quote Originally Posted by Bill Dufour View Post
    The minisplit indoor head is not magic. It is just a coil and fan with some wiring with a drain trough for condensation. No reason it could not be taken apart and put into a tin box with regular size, easy to change, filters on the air intake side.
    Bill D
    You don't even have to go through all that trouble. They make mini-split head units designed to work with duct work and fit between standard spaced joints. They are a bit more expensive than the much more common wall units.

    2022-08-28_235632.jpg
    Here is a Fujitsu unit but many of the mini-split companies have similar ducted assets.

  14. #14
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    Something I would play with if I had a ducted unit would be an outdoor air intake. You can automate a damper to actuate when you turn on your dust collection(mine vents outside).

  15. #15
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    Massachusetts has a program to cut down on carbon dioxide pollution, which contributes to climate change. They are giving $10,000. rebates on mini splits in houses and shops. Combined with the 10 KW solar system I have, it looks like I can just about eliminate the propane heat. I will keep it as a back up for when the electric lines are down. Our solar panels have to be tied into the grid, because we get paid for the power we produce.

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