Hyperheat ductless minisplit vs. gas combi boiler
I live in a 1600 SF 1956 ranch house in MD currently heated by an oil fired boiler with hydronic fin tube baseboard and cooled by a separate cooling-only forced air system whose ductwork does not extend to 2 bedrooms on the north end of the house. The oil system is old and expensive to operate (burn about 700 gal/year) and I’d like to get completely off heating oil when it gets replaced in the near future. Natural gas is available in my neighborhood, but the gas main would need to be extended farther down my street at a cost of $7000. I plan to be in the house 20 years. I’ve slowly picked away at insulation and air sealing, but I’ve done about as much as I can without having to start ripping out walls and ceilings.
I’ve had several HVAC contractors assess my situation, but most have either wanted to sell be a replacement conventional oil boiler or to swap the cooling system for a heat pump with electric heat strips. I do not feel a replacement oil system is a good investment over the time span I’d like to remain in this house and I feel the traditional heat pump will not offer operational savings or comfort. The existing ductwork is a “spider” of flex duct in the basement/crawlspace which I understand may be a disaster for heating comfort and efficiency.
The one contractor who offered alternatives proposed one of the two solutions:
1. Mitsubishi Hyperheat ductless system with (2) 30k outdoor units each supporting (3) heads as follows. Outdoor unit 1 – (1) 15k living room; (1) 9k master bedroom; (1) 9k kitchen. Outdoor unit 2 – (1) 12k basement; (1) 9k bedroom 2; (1) 9k bedroom 3. Estimated cost ~$18k inclusive of demo of the existing boiler, tank, air handler, and outdoor condenser and 12 year parts and labor warranty.
2. Replace the oil boiler with a gas Navien combi boiler. Estimated cost ~$17k inclusive of the utility running the gas line to the house and one year parts and labor.
Contractor was really pushing the ductless but when asked for references who are doing 100% of heating of a house of similar age, type, and size to mine with ductless hyperheat has gone silent.
It’s really been difficult for me to get a good handle on which option will be cheaper to operate, offer the best comfort, and be the best overall “investment” for the long term. I’m also not sure if there are other alternatives out there that would be less expensive on the installation. The costs I’ve noted above will have fairly long paybacks. Sorry for the long post – thoughts and insights are much appreciated!
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I'm a builder in New Hampshire in a 2600 SF old house. After building several new homes with air source heat pumps aka ductless minisplits, I tossed my oil fired hot air furnace, shut off my propane boiler and installed three 12k Mitsubishi Hyperheat minisplits. No regrets. Our house is far more comfortable year round. The kitchen does get chilly (65 oF) when temps are below 0F, but better weatherstripping on a couple of old doors should help that. They are also less expensive to run than oil and gas - before solar. In addition, with our solar panels now up and running, we've had six months (and counting) of free utilities. As far as home upgrades, the my best advice for you is to minimize air infiltration and verify with a blower door test. Overall, my advice is to go with the minisplits.
Two 30K cold climate multisplits capable of delivering a combined 57,000 BTU/hr @ +5F sounds like a terrible "solution" (to anything but the contractor's boat payments.) That's probably twice our actual heat load, and the 9K heads in the bedrooms & kitchen are bound to be CRAZY oversized for the actual heating & cooling loads of those rooms. Unless it's a walk-out basement with no foundation insulation the 12K head in the basement is probably oversized too.
If the cooling ducts are in a basement or conditioned crawlspace it's possible that the existing ducts or a fraction thereof can be used with a Fujitsu mini-ducted mini-split, with some other solution for the other rooms. A pair of 3/4 ton -9RLFCDs is good for about 12,000 BTU/hr each (24K total for two), and they make them as big as 1.5 tons, which is good for over 20KBTU/hr (each). Unlike the oversized multi-split solution, these things modulate with load, and will provide much steadier, stable room temperatures. They can throttle back to about 3 KBTU/hr each at +47F, and even a pair of them would have a lower minimum modulated level less than the minimum output of 7200 BTU/hr than just ONE MXZ-3C30NAHZ delivers (which it would be delivering to a single 6K head, not evenly distributed to the house.)
The "spider" approach of flex duct can actually be pretty reasonable if the flex is stretched tight, going to a short fat plenum. If it's a bit saggy or not well sealed it can probably be re-commssioned rather than replaced.
A Navien combi boiler might work if you have sufficient radiation per zone to run it at condensing temperatures, but it doesn't air condition, and the quoted price is about twice what people are charging in my neighborhood.
Most 1950s vintage 1600' ranchers with modest efficiency updates would have a design heat load between 20-30,000 BTU/hr at MD type out door design temps. With a serious round of air sealing, foundation insulation and beefing up the insulation elswhere it can probably be brought under 20,000 BTU/hr. Since you have a heating history on the place, start by running a fuel-use based load calculation :
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
That will put firm stakes in the ground around the whole house heating load, but won't tell you the room by room loads. But with the baseboards in each room you can infer the room by room loads as a percentage of the total by comparing the length of the room baseboards to the total run of baseboards. Using an online Manual-J calculator such as coolcalc.com or loadcalc.net isn't super-accurate for the actual loads (but way better than a WAG), but would be able verify the proportional numbers too.
How many zones, how much baseboard per zone? This is an important aspect for figuring out if the Navien solution makes any sense too. Run your own napkin math on that one too:
https://www.greenbuildingadvisor.com/article/sizing-a-modulating-condensing-boiler
The new minisplits and multisplits provide plenty of heat at the temperatures you are likely to see in MD, and can certainly be a good alternative to oil and gas.
However, your minisplit dealer is a charlatan. 5 tons of heating/cooling in a 1600 sf house equals one ton per 300 sf. If you were living in an uninsulated barn you might use that much heat. Take a look at Bob's post above. He heats his house in NH with half that much capacity and his house is twice the size and two climate zones colder. A back of the napkin calculation based on your fuel oil usage suggests that something close to 20k btu would probably suffice.
Don't even consider hiring a HVAC contractor without performing a good manual J load calculation. You simply can't properly specify equipment without accurate load numbers to start with. You can find people online who are independent from your HVAC contractors and don't have a vested interest in overselling the equipment. Alison Bailes is a contributor here. He's in VA, and he does this for a living. Give him a ring.
>"Don't even consider hiring a HVAC contractor without performing a good manual J load calculation."
+1 on that!
And don't let the HVAC contractor run those numbers- hire an engineer or RESNET rater, somebody who makes a living & reputation on the accuracy of the numbers rather than installing & maintaining equipment. In my neighborhood that service usually costs between $500- 10o0 depending on the complexity (and seemingly the average income in the ZIP code), but it'll usually save you more than that in up front equipment costs.
A fuel-use load calculation and proportional baseboard approach will get pretty close, assuming the room to room temperature differences are pretty small with the heating system as-is. Make note of any rooms that are traditionally too cool or too warm for making adjustments.
>Alison Bailes is a contributor here. He's in VA, and he does this for a living.
Last I heard Allison Bailes was still living & working in GA, not VA, but I understand they will do Manual-J's remotely based on information provided by the homeowner/contractor.
Thanks for the correction. You're right - Alison is in GA. But he does do long-distance Manual J calculations, so far as I know.
I really appreciate all the thoughts here. I had toyed with the idea of getting an independent manual J done in the past so I will probably go ahead with that. I like the idea of the ducted splits but finding a contractor to install them (and at a price that won't break the bank) may be challenging, to say the least. Any tips for finding and engaging an enlightened contractor?
>Any tips for finding and engaging an enlightened contractor?
Become your own enlightened contractor (in an unofficial "general contractor" sort of way.) By getting an independent load calculation it gives you the opportunity to specify the equipment and put it out to competitive bid.
Finding a contractor comfortable with mini-duct cassettes (and who will take direction on that) is sometimes challenging. Fujitsu has a "installer finder" web page:
http://contractors.fujitsugeneral.com/
Other mini-split vendors have mini-duct cassettes, but Fujitsu units have more cold temperature capacity than most of their competion, and can handle more static pressure/longer duct runs.
A few years ago I specified a 1.5 ton Fujitsu on a project I wasn't directly involved with (no direct management, only long-distance advising). The contractor local to the project who claimed experience with them flat out refused to install it unless it was installed in the attic (above the insulation) , not the basement, in a location with a 99% outside design temperature of +12F. That would have destroyed the as-used efficiency, and the homeowners went with a less than optimal 2-ton ductless multi-split solution instead, a decision made in desperation due to the impending heating season. It works OK, not great- some rooms run on the cold side. The mini-duct solution would have been both more comfortable and more efficient, but only more efficient installed inside the thermal & pressure boundary of the house. Had it not already been into November I would have advised them them keep searching for a contractor willing to take direction rather than settle for "Plan B".
Which is all to say plan ahead, and be prepared for some push-back. You may have to push back pretty hard on some contractors to get the right equipment installed, in the manner that you want it installed.