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Can an appropriately sized mini split handle 6 Air changes per hour?

Our current gas boiler and air handler are failing and so we are looking into replacing the system.

We have had a few heating/plumbing companies out to provide bids and options and multiple have suggested mini splits given our existing system and the improvements we'd like: A/C and multiple zones.

However, we had a home heating efficiency person come evaluate the house, as it is required to get local rebates, and they said mini splits would not work. They said because our house is at 6 ACH the mini splits would be using a ton of electricity and would not really work to keep the house warm and we would need to supplement them some how. For reference we're in Colorado so can expect below freezing lows through much of the winter, but highs in the 50s.

I have been trying to research the capacity/effectiveness of mini splits for this ACH but haven't found anything helpful.

Thanks in advance for any help.

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    What's providing your ACH? Is it an HRV or ERV? The answer is way different if you're bringing in untreated air vs doing some heat or energy recovery.
    – KMJ
    Commented Dec 13, 2023 at 6:38
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    @KMJ, it's a measure of air-tightness
    – Tiger Guy
    Commented Dec 13, 2023 at 10:41
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    The key number you need is how many BTUs per hour are required during peak heating season. Another factor is that minisplits do not distribute heat/cool whole-house. They heat and cool local areas. As someone who lives in cold climates similar to Colorado, I would not rely on minisplits during the winter. They make for good supplemental heat and primary cooling. Their efficiency drops dramatically even for units rated for cold weather. Get a qualified HVAC company to provide you with a Heat Load Analysis. Then select minisplits that are efficient during heating season and can meet that load.
    – John Hanley
    Commented Dec 13, 2023 at 19:16
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    Another item. Once you go beyond 12K/24K with minisplits, the costs add up quickly for many zones. Since you already have a boiler, you have central ducting. You might find that is less expensive in the short term and long term to add a gas furnace and central air conditioning. I would go with that and add a minisplit to handle peak loads. In my last house, we had gas heat. I added a minisplit for the living room and master bedroom which meant the furnance did not run as much and temperatures stayed constant while reducing the utility bills for most months.
    – John Hanley
    Commented Dec 13, 2023 at 19:22
  • Thanks John. The combination of keeping the boiler and adding mini splits is something the efficiency expert recommended, but none of the 3 heating companies we had out suggested.
    – r_alanb
    Commented Dec 14, 2023 at 15:08

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An appropriately specified set of mini-split heat pumps will handle your heating needs, 6 ACH is fine. These heat pumps are relatively new up north, and if your area has had cheap natural gas for a long time, that will just be the standard answer. There is no practical difference between mini-splits and whole-home units in terms of heat output, that recco makes no sense.

The advantage of mini-splits is the good ones are all variable speed, which makes them super-efficient when they aren't running flat-out. Also good for widely varying loads on your house. You might need to change out your breakers from the large ones for your current HVAC to smaller ones for mini-splits. Any HVAC installer that does mini-splits in your area would be very familiar with what you need.

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    Thank you! Edited typo above- we want to add A/C and multiple zones. Thanks!
    – r_alanb
    Commented Dec 13, 2023 at 15:13

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