Seeking Ideas for Replacing Baseboard Heat
We have a property in Zone 6A that contains two buildings – one is a 600 sq. ft. studio, the other is a one-bedroom 1000 sq. ft. house. The studio is heated with a kerosene boiler, the main house uses heating oil; both drive hydronic baseboards. Both buildings are single-floor, circa mid-1960s, and have tons of double-pane glass and foam-board insulation (I believe it’s R5), thus there are baseboards all over the place.
I’ve looked into the following options for each:
* LP combi boilers – Viessman or perhaps IBC
* Mitsubishi Hyper-Heat Mini-Splits, w/floor-mounted handlers
I was initially going to go with the combi boilers, but the price of propane started to scare me, as well as the fact that I’d need to have four very large bottles outside, which is an eyesore. It does address the problem with DHW, though, which is an issue since the studio uses the boiler for it (the main house has an electric hot water heater).
I’m leaning heavily toward the mini-splits for environmental and exterior aesthetic reasons, but I really worry about how well they’ll work in practice. The fact that you need to have a backup heating source is making me a little nervous, especially because I’d really like to get rid of the old boilers and fuel tanks.
Is there a better option for heat out here? The two buildings are very close to one another (maybe 30′ between them), and it would be amazing to have some sort of shared heat and treat the studio as another zone of a larger heating system. I don’t know much about Chiltrix, but that sounds like it could be an interesting alternative to the Mitsubishi unit?
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Replies
>"The fact that you need to have a backup heating source is making me a little nervous, especially because I’d really like to get rid of the old boilers and fuel tanks."
What makes you think you'd need a backup heating source? There are mini-splits and cold-climate ducted heat pumps with bigger air handlers with fully specified output down to -22F/-30C.
What is your local 99% outside design temperature? If you don't know, guesstimate based on a nearby listed location here:
https://higherlogicdownload.s3.amazonaws.com/ACCA/c6b38bda-2e04-4f93-bd51-7a80525ad936/UploadedImages/Outdoor-Design-Conditions-1.pdf
Hyper-heating heat pumps with full sized air handlers usually come with electric auxiliary strip-heat options as "backup", if it's somehow required by local code.
Start with a room by room Manual-J type heat load calculation using aggressive (per the instructions in the Manual) rather than conservative assumptions on R-values, air tightness, etc. Freebie online Manual-J-ish calculators such as LoadCalc.net or CoolCalc.com are good enough for first cut, provided you're sufficiently aggressive.
Reversible chillers (Chiltrix, Arctic, et al) may require more design skills and ancillary hardware to make it really work well than the average DIYer is up to, and the product support is likely to be less available than with name brand mini-splits. Just about any manufacturers' hyper-heating mini-splits or ducted heat pumps are more forgiving to spec and set up than chillers, and come pre-outfitted with automatic pan-ice management heaters & controls.
Thanks for the reply, Dana! So, I've talked to three installers about the Mitsubishi Hyper-Heat (e.g. MXZ-3C30NAHZ2) mini-split systems, and all have said you need to have backup heat, but none have mentioned strip-heat backup.
According to the doc you provided, our 99% outside design temperature is -3 degrees Fahrenheit. I just tried doing the Manual J, and it said the main house was at about 42K BTU heating, and 20K BTU for the studio. Interestingly, the mini-split estimates I have in hand are short for both of those - 30K and 18K - so we might have been in for a very cold winter.
I'm definitely not going to DIY it, so I'd rely on expertise from the vendor to make sure everything is spec'ed correctly. The things that are drawing me to the reversible chillers are that they also do DHW, and the fact that they have backup heat built-in. But maybe the mini-splits are a better choice since they're so common in addition to the benefits you've mentioned?
>"According to the doc you provided, our 99% outside design temperature is -3 degrees Fahrenheit. I just tried doing the Manual J, and it said the main house was at about 42K BTU heating, and 20K BTU for the studio."
42K at -3F seems CRAZY high for a 1000' house that has fluff in the walls & attic, glass in the windows, and doors that shut. The 20K for a 600' building seems high too, unless it has a lot of windows (12-15K would be more likely for a 600' tight 2x6 shop with reasonably low window area. )
Which tool did you use?
How much of that load was infiltration & ventilation?
The MXZ-3C30NAHZ2 is only good for about 25K at -3F, and would need massive backup if your heat loads are actually that high (not likely).
https://ashp.neep.org/#!/product/26173
Full size Mitsubishi air handlers have strip-heat options. Asssuming you'd even need anything as big as the MVZ A30 (34,000 BTU/hr of heating, when married to an adequately sized MXZ compressor) it has multiple strip heat "toasters" designed to work with it:
https://mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.com.s3.amazonaws.com/DAMRoot/Original/10003\M_MVZ-A30AA7_For_MXZ_MULTI-ZONE_SYSTEMS_Submittal.pdf
https://mylinkdrive.com/viewPdf?srcUrl=http://enter.mehvac.com.s3.amazonaws.com/DAMRoot/Original/10003\OptionalElectricHeatKit_Submittal.pdf
There are others:
https://mylinkdrive.com/USA/M_Series/R410A_Systems-1/Multi_Position_Air_Handler-2
The P-series compact duct cassettes can work with higher loads too:
https://mylinkdrive.com/USA/P_Series/R410A_Systems-4/Horizontal_Ducted
Yeah, I suspect I completely screwed up the manual J. I used loadcalc.net to perform the calculation. The numbers are probably high because both buildings have VERY large glass windows on most sides, but I may have overcorrected for that. I will give it a shot again tonight.
Thanks for the info on the other options - I hadn't looked into any of those before, so more food for thought.
I am not clear on your goal. Is it to be more comfortable, cheaper to run or just less ugly? You need to consider the HVAC system in context of all the building elements to be improved. So are you going to improve the insulation and air sealing? Heat load is a function of these elements. Do you need cooling? Does the HVAC systems need to be hidden or are in-room elements acceptable? How much of a premium are you willing to spend on your enviromental philosophy? Are the buildings adaptable to new system? Basement or slab?
Sorry, to clarify my goal: We have two buildings with ancient, on-their-last-leg boilers feeding baseboards. I'm optimistic they will make it through this heating season, but less so for next. So we need to find replacements that will ideally get the heating oil company out of the equation.
> So are you going to improve the insulation and air sealing?
Air sealing is something that I plan to do at the same time as the HVAC installation, and insulation is on the table but not yet prioritized.
> Do you need cooling?
Nice-to-have.
> Does the HVAC systems need to be hidden or are in-room elements acceptable?
Ideally it would be hidden, and I really don't want mini-split heads high on the walls, detracting from the views. That said, there's the reality that I'll have to deal with that some of it will be visible. I think I've come to terms with a floor-mounted fan coil or mini-split head, but sure, the less visible the better.
> How much of a premium are you willing to spend on your enviromental philosophy?
There is a limit, but I'd probably err on the side of a more expensive electric option over fossil fuel given the recent energy trends.
> Are the buildings adaptable to new system?
Not sure what you mean?
> Basement or slab?
Basement, but one of the buildings is cantilevered such that it has about 20% exposed underneath.
I run a Mitsubishi hyper heat without backup of any kind. 20 days below zero and still going strong.