Ducted minisplits for an old house
Hello! I am in the market for a partially-ducted minisplit system in Zone 5A near Albany. The 1.5-story farmhouse was built in the 1850s and is currently heated with a wood stove and electric baseboards that are contributing to $500+ electricity bills in the winter. The exterior walls have fiberglass insulation from an ~’80s remodel and original windows with aluminum storms. The current whole-house heating load at the 99% design temperature is 38k BTUs, calculated using room-by-room data from Mysa smart thermostats on a very cold February day.
We’re planning some major envelope upgrades in conjunction with the minisplit install: applying closed-cell spray foam to the rubble foundation from the inside and, if we decide to put a ducted unit in the attic, air-sealing & insulating the underside of the original slate roof using a closed-cell foam assembly with a 1” air gap, similar to this one: https://buildingscience.com/documents/enclosures-that-work/retrofit-building-profiles/ma-jamaica-plain-ngrid-comprehensive-three-family-triple-decker-building-profile
We’re planning to take the Allison Bailes approach of slightly undersizing for the current heating load, perhaps keeping some baseboards in place to provide supplemental heat on very cold days.
Our main reasons for wanting a partially-ducted system are (1) to improve evenness of conditioned air distribution throughout the house, (2) to avoid oversizing individual heads, and (3) to allow for proper air filtration—a future-proofing necessity, we feel, with all the wildfire smoke.
We’re considering either a Fujitsu or Mitsubishi system. I have a few foundational questions as I begin my search for an HVAC contractor:
1. Do either of these manufacturers yet offer low-temperature, single-zone, low-static ducted models?
2. Does it still hold true, as many have said on GBA in the past, that Fujitsu is better than Mitsubishi for ducted systems?
3. Should I consider talking to contractors who are well reviewed but not listed on the manufacturer’s website as certified installers? Or should I pick a manufacturer and limit my search to that company’s list?
4. Should I assume that a ducted system will require a third-party HVAC design service? Or is there any circumstance in which I should put my confidence in an HVAC contractor to design it?
If any of my descriptions or questions point to flaws or gaps in my understanding, or if there are better approaches, I’d welcome any advice to set me on the right path.
Thanks very much!
Doug
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Replies
for the small size I looked this one up the other day
https://www.ecomfort.com/Mitsubishi-SE-KD12NAH/p107669.html
dunno about the bigger ones
Very cool, gusfhb. Thank you for sharing!
I'm relieved to see that at least Mitsubishi does some single-zone ducted units.
Another potential advantage of Mitsubishi over Fujitsu is that they seem to have more certified contractors in my region.
One potential disadvantage of these Mitsubishi units: as far as I understand, unlike Fujitsu they can't be installed in a vertical orientation. (Though I left this out of my original post, I might forego the attic installation and instead install a vertical unit in an upstairs closet to serve the two main bedrooms.)
The unit I linked is meant to be installed in a soffit or in a closet ceiling
i would guess that two of them in different spots in your house might be the ticket for you
Good questions that I am Interested to hear answers to as well.
Are you limiting your search to low static? I know Mitsubishi at least makes mid static multiposition air handlers that can be vertical. To check out Mitsubishi products, I recommend mylinkdrive .com
Thanks Tyler! I’d consider mid-static for sure. Thanks for the tip.
This is a great resource for looking at different products:
https://ashp.neep.org/#!/product_list/
On the ducting configuration drop down select "single zone compact ducted". Most manufacturers offer both a low and mid static unit.
If you are looking for vertical mounted another option is the Carrier/Midea units, I've used both 12k and 18k units with good results.
The one issue with the Fujitsu ducted unit is the outdoor unit does not come (at least last time I checked) with a base pan heater. In my climate (north edge of zone 5), this would create issues as usually there is large piles of ice under the outdoor unit from defrost cycles.
Thanks Akos! That NEEP database is so helpful. And great insight about the heat pan—I’m also near Zone 6, so certainly a concern.