Choosing an ASHP in Climate Zone 5
We’re close to completing the design of a new construction ranch home in Omaha, Nebraska. I really want to do an all electric home, and I’ve expressed this to our builder. I’m not in the building industry but I have spent the last 2+ years learning about building science, watching videos and reading articles. After much research, including the Q&A section here, I have a preferred HVAC setup. Mitsubishi Electric Hyper Heat single zone outdoor unit, paired with a traditional air handler and ducting. There are several reasons I like this approach. It allows the addition of heat strips for backup depending on how the load calculations go. We can integrate ventilation if needed, although I prefer a separate duct system. It also seems like a simpler setup that our market is used to. First question: Would a mini-split setup be preferable in my situation?
I’ve expressed this to my builder and he says that his HVAC contractor says that ASHP are not appropriate for our climate. I responded that information seems to say that’s not true. I’ve also discussed with some local HERS raters that work with our builder. They said that ASHP can definitely be done, but they believe that a natural gas backup is a better fit. If the backup isn’t used much, I’m not that opposed to this solution, but it seems like that would be more expensive than heat strips. Second question: I just don’t know what to do. Should I relent to the local knowledge base or continue to fight for an ideal setup? Should I hire EnergyVanguard or similar company to do the calculations? I’ve made calls to HVAC contractors but haven’t gotten great responses. The best was that “that is possible”.
Details on home: Main level is 1800 sq ft with a full basement with the same space for a total of 3600 sq ft of conditioned space. Setting the goal for 1 ACH50. 2×6 walls and trying to fit Zip R-9 sheathing (with blown in cellulose) and continuous rigid foam on basement walls (with blown in cellulose). R60 in the attic. No subslab insulation. I argued for this but relented because I don’t know if it’s the budget and everyone was fighting against it.
Thanks,
Matt
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Replies
Hi Matt,
I have a ducted Mitsubishi hyper heat, and I highly recommend it. We only get into the single digits here, so I have no backup strips but it handled the single digit weather just fine. I’m not sure what your first question means: the ducted Mitsubishi is a mini split. Mini split is now a confusing term, ducted vs. ductless is usually what people mean. Ducted is the way to go in my opinion. Is that what you were asking?
There seems to be a lot of hand holding necessary to get contractors on board, but I somewhat understand the hesitation. If they’re scared, adding electric or even gas backup is not that difficult. If you go with gas backup, get the least efficient, cheapest furnace you can since it’ll probably never run anyway. Sounds like your house will be well insulated and tight, so you’ll have high comfort, congrats!
Thanks Paul! It was a confusing question on the mini-split. Maybe multi-head would be a better term. To clarify, instead of a single air handler, going with a multiple ducted or ductless heads. You answered the question though, you'd recommend a single ducted air handler.
Thanks again,
Matt
Yup. Ductless heads are the worst option for a new build, only to be used when nothing else can be done. There might be a case for multiple ducted units - maybe one on the first floor and one in the basement. If you can, two separate outdoor units would be great in that situation.
I think you need a different contractor! It seems he believes he can’t make a heat pump work in your climate and I believe him, he is incompact.
Find someone that believes in heat pumps and they will succeed.
My Rheem 17 SEER HP provides 100% of my heat when it is above 7°F
If it makes your installer feel better let him install the largest electric back up heat if you have room for the 3 breakers in your panel.
I think multi headed mini splits are a mistake.
Walta
Thanks Walta! I told my builder that we should look at other contractors and I've called around myself. Some have done ductless mini splits but none had done this particular setup. I'm wondering if a third party hvac design would be best.
Matt
We have a 2-zone ducted Mitsubishi Hyper Heat system and love it. We have a MXZ outdoor unit (now the Smart Multi) and a pair of SVZ air handlers. In our case, we kept our boiler, so we have hydronic coils as backup heat, but heat strips are fine too. We hit -13F here in February and the system performed great!
That's great that it was able to keep up at -13F! Our design temperature is -2F, but we can hit those temperatures a few days a year.
our design temp is 9F, so that was quite a dip!