Number crunching

Thanks very much for the links! I spent an hour going over the one in Maine. Great story of a DIY house. I have nothing but respect for his skill and determination. It is a shame he forgot the Earth tubes as I expect that could have helped his efficiency and comfort.

Earth berm homes can have issues with air flow, frost heave and interior air quality.
If done correctly, they are great. If not, they can be a nightmare. Mold is one of the biggest pitfalls I’ve come across.

Also, forgive my misunderstanding, I thought you were referring to the Passive House standard. Now I understand you are referring to passive solar gain. I agree, passive solar is the best bang for your buck (almost free).
So when I said ‘super expensive’ I was referring to the standard, not the passive solar strategy.

The Maine berm builder mentioned the frost line rarely getting down to four feet. In Minneapolis, we need to go down six feet. Building on grade is almost never done in residential buildings here. And the cedar shingles would be a nightmare, requiring frequent replacement.

I loved his metal roof and lots of other aspects of his build. It just wouldn’t work in MN, especially in northern MN.

I’m trying to figure out the size of the house, and approximate location…

Holy cow, sounds like a very poor install/design job, which unfortunately usually ends up with results as you listed.
I have first hand knowledge of both types of installers. Bad ones will cost you money, good ones will save you money.

I have 300% return ( a little more actually) and pay for no diesel. My electric usage (ignoring the solar panels) is about 10% higher than the US average. That include heat, water heat, cooking and charging both electric cars (until yesterday).

 

Getting back to the original post, you give a good example of why I didn't replace my 2010 Prius with another hybrid. Once we got our Rav4 hybrid, the Prius became a secondary vehicle logging about 3,000 miles per year. You don't save much fuel with a hybrid at that rate. So, like you, I got a Mazda, a CX-30 that I like a lot.

 

Yes, with all the digging he had to do to prepare the site, the addition of the geothermal would have been easy. But still would add an expense in construction and installation, which I do not know the detail.

I can see the airflow can be a problem with earth shelter especially if it is a multi-roomed conventional house design. I would think the simplest way to avoid the problem is to keep it a simple open space. But I am sure site preparation for a good drainage is a must.

I had to look it up and I see it now.
https://en.wikipedia.org/wiki/Passive_house
Yep, that is a quite different thing than what I was thinking of. Passive solar (mostly for heating) is the least expensive way to heat a house without using any other external energy.
https://en.wikipedia.org/wiki/Passive_solar_building_design

The Maine homeowner mentioned in the link must live in southern Maine. But still, 4 feet frost line is quite rare in my state. The map below was drawn based on data from the U.S Department of Commerce NOAA. According to this data, even the southernmost Maine has a frost line of 60". I live in an area with an 80" frost line. Certainly not as deep as the northernmost part of MN where it reaches 100".

Our current house is earth-bermed but with absolutely no passive solar design for heating. Half of our house is earth-sheltered below grade, but this happens to be the south-facing side. And there is no window for solar gain on this side. The north side of the house is exposed and has a lot of windows. I should have spotted this gigantic design flow when I was looking for a house to purchase... but it was the middle of summer when I looked at it. The house was very cool without AC. And I did not think of what is like 6 months later.

 

Terminology keeps getting in our way

An "Earth tube" is not geothermal in the traditional sense.
The cost is almost nothing. It is basically a way to get outside fresh air flowing into the furnace intake at 40-50 degrees year round rather than whatever the ambient temps are outside.
Installed correctly they can be great.

Here is a good summary. Although they mention large cost, I suspect that is almost all labor. If you are digging the trench yourself, they can be useful.

As with a bermed house, there are a number of pitfalls, the design and execution are very important. But they can give nice benifits.

**PS**
Oh, and I found the Maine builder's dimensions. The exterior of the foundation is 960 sq ft. After walls and such, about 900 sq ft is my guess. Again, great home, fairly efficient but not nearly as efficient as net-zero or Passive-House homes.

However, for bang for your buck, he did an awesome job.

 

With soring heating oil prices, I have decided to update our home heating to curve down our dependency on oil. Initially, I thought the cheapest and simplest would be installing an additional wood-burning stove in our kitchen/dining room where we spend quite a bit of time all day long. As it turned out, installing a full chimney system in this room is very costly. Also, the room is rather small for a full-size stove and doesn't have much floor space to spare. A small cylindrical-shaped Euro design wood burning stove, MORSØ 6140 as shown, was the only model that would satisfy our space requirement, but it is almost three times the cost of the smaller rectangular firebox stove such as Jøtul F 602 V2. The cost and space requirements, plus the work involved in keeping the fire going in the wood-burning stove prompted me to look for different options.



I started looking for a pellet stove. A space-saving wall mount type like the AP5000 by US stove with the direct vent system would work the best. I have not checked with a contractor for the installation cost yet, but it seems the cost will be substantially less than the Morso wood stove option. But, with a pellet stove, I would have to buy bagged pellets from the store and haul them. Then I need a dry storage place for them and still have to load the hopper at least several times a day to keep the fire going. Just not as convenient as the next option.


The third and probably the most convenient option is the heat pump. I considered this option before but dismissed it due to the fact that electricity cost is quite high here and that the coldest months may be too cold for the heat pump. But at the current cost of oil, even already high electricity started looking cheaper option. So, I revisited the idea of installing air sourced mini-split heat pump. Although I have a suspicion that it will not heat the room all winter long, it should curve down the amount of oil burned. And as turned out, there are better state-backed incentives on heat pumps such that this option would be the least expensive to install, although the cost of operation may be the most expensive of the three choices.

The installer came and sized the unit. The estimate is based on the Mitsubishi heat pump system, MUZ-FS15NA-U1 (outside unit), and MSZ-FS15NA-U1 (inside unit). It has a heating low limit of -13°F (-25°C) with SEER 22.2 (or HSPF 12.5) whatever that really means. They also have Fujitsu and Daikin, but for some reason, Mitsubishi units are the ones they recommended. Maybe more profit margins for them?

Does anyone have experience with this Mistubishi ductless system, especially in a colder climate? The AC capability is not very important for us, I would probably use AC for less than a week. The biggest question is how much heat it will "generate" or I should say "extract from the cold outside air" to make the room comfortable in winter without the oil burning.

 

Those are excellent SEER and HSPF ratings for a Heat Pump.

Our Heat Pump System has similar SEER and HSPF numbers and it does an excellent job in the winter providing heat, however it is a duct based system.

I wonder if your contractor could refer you to a customer where they have installed one of the units?

Would this offer apply to your situation? It is a $500 off offer.
Mitsubishi Electric Heating and Air Conditioning (mitsubishicomfort.com)

 

@Salamander_King

Try this website, it's a great group of HVAC Professionals and they would be more than happy to provide you with some advice and information. The vast majority of them are very focused on high quality work and customer service. There are very likely several mini-split experts on the site. They also have a contractor locator map available that shows the location of the professional members, to make it easy to contact one if you're interested in contacting them.

https://www.hvac-talk.com/vbb/

 

Yeah, the reason I was considering a wood stove is that we have free wood to burn. I never have to buy firewood, as long as I am willing to fell a tree, move it, cut it and split them, and stack them... But I am not getting younger. That's very hard labor.

I contacted another local HVAC installer who specializes in Fujitsu units for a site visit and estimate, but they are booked until Aug. I made an appointment with them, but I may go ahead and use the one who came and recommended Mitsubishi.

Great idea. I will ask for references. Also thank you for the link to the promotion ads. I have to contact them to find out the detail. It sounds like the rebate is only for the customers using the specific installer... but it is worth checking out.

EDIT: Realized the small print on the page. It reads "Limit one $500 instant rebate per multi-room system sold on single-family residential installations. Discount is flat $500 per qualifying system purchased from and installed by a participating contractor between 4/5/2022 and 6/30/2022. Limited to systems purchased in IA, IL, IN, KY, MI, MN, ND, NE, OH, SD, WI and WV." Unfortunately, I don't live in the states mentioned.

Thanks for the link. I will check it out.

 

If you use facebook, there is a group called ‘electrify everything’ (https://www.facebook.com/groups/1854210748209867)
There is a ton of hands on experience with heat pumps.
For what it’s worth, I have also heard Mitsubishi has some outstanding heat pumps.

 

Thanks for the info. Unfortunately, I don't use FB... used to, but I am glad now I don't even have an account.

Yeah, from what I can find out on internet searches, Mitsubishi units seem to be highly rated... Certainly, I have much more confidence in the brand than in some DIY kits like MRCOOL for example.

 

I just had the not-quite-so-cold-climate Mitsubishi MSZ-GL12NA installed for the master bedroom a week ago today, but that was just 2 hot days / no cold days ago. It is rated to only -4F, plenty for my climate zone but not yours.

My unit was ordered in early December, with a lead time of 6.5 months. Three other installers could install other units with various lead times of ten days to three months, but at much higher costs, plus a few other considerations that lead me to make this particular choice.

I also have a 13 year old Fujitsu at the other end of the house, rated down to only +5F. Since then, for reasons unknown to me, installers in my area seem to have mostly abandoned Fujitsu. When/if this one fails, I'd probably replace it with a Mitsubishi -GL18. I have no reason to expect to need replacement soon, but am just keeping track of the markets for this and for heat pump water heaters. My heat pump water heater is no longer supportable (the maker went bankrupt years ago), and I've had to make one electronics repair already, so am keeping up with the market for when it has a bigger failure.

Have you looked at the heating capacity vs ambient temperature specifications and charts? If not, I'll try to link some later today, after other activities. Remember that as it gets colder and you need more heat, the unit is able to provide less, so it is more of a puzzle than sizing other heat sources. I had the advantage of being an engineer who recorded very frequent electric meter readings through some previous severe cold snaps (by this area's standards), so had some basis for modeling heating demand vs temperature for my particular house. The house's envelope has been improved since those recorded cold spells.

For heating, you don't care about SEER, only HSPF. For efficiency comparisons, electric resistance heat has an HSPF of 3.412.

 

When I contacted an HVAC installer, I did not specifically ask for particular models. It is just that the first HVAC installer who came by for a site evaluation recommended the Mitsubishi FS model with 15000 BTU output for our application. I also asked about the multi-room installation, but that would require a duct or additional independent outside unit, so it becomes too expensive. Apparently, MUZ-FS series is the newest 2021 model with the best heating performance. According to the spec sheet, it performs 100% heating capacity at -5°F and 70% to 81% heating capacity at -13°F.

This model must be too new to be included in the ENERGY STAR Most Efficient 2022— Central Air Conditioners and Air Source Heat Pumps yet. I don't see this particular model on the list. FS series must have replaced the previous hyper-heating model FH series which had an HSPF rating of 12 for the 15000 BTU unit (MUZ-FH15NA). Looking through the ENERGY STAR list, Fujitsu has several lines of models with a rated capacity of 14500 BTU with HSPF 13.4 which is a slightly better number than the Mitsu FS model. The Fujitsu models are rated to be operating temperature down to -15°F whereas Mitsu FS is down to -13°F.

I am going to ask the installer if they have access to the Fujitsu models and if they do, what the cost is. In the ENERGY STAR list, besides the Fujitsu, the only other makers with HSPF12.5 or higher for a 15000 BTU capacity mini-split heat pump are Daikin and LG. But those are all just spec numbers on paper. The "real-life" performance may not be as clean-cut as the numbers suggest.

 

Good that you are looking at real datasheets, so that you can see and properly consider the impacts of cold ambients. Some snags to watch out for are that different brands and even model lines pick their nominal unit ratings differently, so a 15,000 Btu/h unit from one line could have significantly different outputs than a similar-nominal unit from another line. All units seem to have 'rated' outputs less than 'maximum' outputs, and it seems likely that the HSPF (and SEER) scores are based around nominal ratings, not max ratings. HSPF scores are based on a weighted average over a particular ARI (Air-Conditioning and Refrigeration Institute) Climate Zone profile, and your sheet shows it for the usual Zone IV. But it sounds like you a might live in the colder Zone V, so your seasonal efficiency would be a bit lower. Though still far better than electric resistance.

I was looking for a 9,000 Btu rating for my secondary unit, was even wondering if the few smaller 6-7,000 Btu units might suffice, and had some particular Mitsubishi and Fujitsu units in my sights. No outfits thought that a hyperheat or -Fx series was necessary here, and three of them pushed for the slightly less-cold-climate -GL line. After reviewing datasheets, plus figured that going off their preferred model palette would greatly increase cost, I figured that to be reasonable. All three of them were figuring that my 9,000 Btu aimpoint was good (or came to that figure on their own when I didn't pre-disclose my own guesstimate).

Two of them bid with the GL-09, while the third suggested the -GL12 because it can throttle down to a 2,000 Btu minimum, while the -GL09's minimum is an anomalously high 4,500 Btu. This not-so-low minimum is out of step with many similar products, and is greater than I'd actually be needing most of the time, so the unit would by cycling on and off in conditions where the larger unit could run continuously at lower power. I'd noticed this before, but this vendor was the only one to disclose it up front. (Plus, they were receiving this unit in full-shipping-container quantities, and were selling it for only $100 over the -GL09. And still had the best bid, though coupled with the longest lead time.)

The fourth bidder (not in chronological order) thought that I needed a larger unit, then bid an old model line that doesn't work down to the coldest temperatures I have recorded here. And he wasn't cost competitive. His bid was dropped the instant I pulled up its datasheet.

 

I should also mention that one neighbor installed a 2-zone Daiken minisplit heatpump. Them being sunbirds and gone most of the winter, I'm one of several people keeping tabs on their house and monitoring the heat, along with resetting a few things after power outages and anything else that needs attention before their return. Their Daiken has been equally as trouble-free as my Fujitsu.

Another (just passed last month) neighbor replaced a central electric furnace with a Rheem Classic single stage ducted heat pump. While it saved plenty of energy and added AC, it is just a fixed single speed, very noisy, turning on with a big jolt. It also has needed one or two unplanned service calls per year.

 

Thanks for the info. I checked both Fujitsu and Daikin sites to check the specs on their extreme low temp heat pumps. Unfortunately, neither of them has spec data comparable to Mitsubishi's data sheet for the capacity and efficiency at the different temperatures.

For Fujitsu, both 15RLS3YH and 15LZASH1 have the same spec but the datasheet shows only one temp point (not even known at what temp).





Daikin's site does not even provide a sheet for the single zone ductless mini-split heat pump. I believe their Aurora Wall mount system, RXL15QMVJU* (outdoor unit) and FTX15NMVJU (indoor unit) for 15,000 BTU capacity having HSPF 12.5 is the equivalent model to the Mitsu and Fujitsu. But I am not very impressed with their website resources. Mitsubishi site has by far the best resource for all documents for every part.

 

Hi here is a link that could help you compare different low temp heatpumpshttps://neep.org/heating-electrification/ccashp-specification-product-list

 

I know some of the comparable Fujitsu data is out there somewhere, because I spreadsheeted some of it. I'll try to re-find the source.