Dude that is for a backup in case my pellet furnace ever has a problem.

Well, it's not too reliable as a backup because the sun only gives you full output a few hours a day and running resistance heat on a battery bank, even a little bit, drains the bank for other things. Just about any other plan is better, including the propane backup.

ICF, I don't think you understand my situation. I am going to be on the grid. The PV is not being purchased just to power a small electric backup furnace, that would be stupid. I will not have batteries to worry about to due to being on the grid. There is no natural gas available and I don't have the physical ability to work up wood any longer, so I cant have a wood stove. Propane here is thru the roof cost wise. IN FACT, if you want to get down to it, even if I heated with electric resistance heat 100% which I will not, it is probably about the same cost as burning propane here when the rates go way up like they are here now. Regardless, I am considering many other options, I think (I KNOW) that I understand that electric heat is not very cost effective nor efficient, so that is why I am looking into other options as well as I would NOT rely on that as a primary heat source, like so many homes still use today........... If my pellet furnace works fine, then the electric would never come on. If the pellet furnace goes down, then maybe it comes on for a few days until I can fix whatever part is broken part or whatever the case may be. I have done the math on what the propane tank and furnace is going to cost as opposed to the electric BACKUP and then factoring in that it is going to be like a parachute, you hope you are never going to use it. Maybe I am not quite so insane.......

In my area the propane costs are NOT regulated by the government commissions like grid power is. So in shortages or when demand is high, the propane companies can triple their costs if they wanted to and there is nothing the regulatory agencies can do.

I am also going 100% electric in my home (grid connected). Mini-splits will be my primary heating/cooling but resistant heating will be my back-up.

Thanks Lbear for your thoughts. Yea propane hits $4.00 a gallon here fairly often. What is that, about 4 to 5 times more than natural gas I think. Just crazy prices. Also thanks for not calling me names)

yes heat pumps have changed - a lot; twenty years ago they could only be used for heat in the south. A single 12,000 BTU unit installed by dealer runs about $3,000 here. Triple glazed high quality vinyl windows are about 10%-20% more than double glazed, and the interior glass surface is much closer to room temperature, so you feel warmer in the house. And if you use cellulose insulation you can probably afford higher R values than you think. Double stud walls are usually the least expensive way to achieve high R values. And, as far as R values, they depend on your climate zone. Most important is air tightness; that should not be compromised for high performance. It's the least expensive, highest return of any step you can take. A very tight, well insulated house does not need heat ducting; the temperatures stay consistent throughout (not counting direct solar gain) - this is probably the least understood and one of the most surprising features of these houses and the reason point source heaters work so well.

At $4 propane an 12 cent electricity resistance heating is cheaper than propane, and heating with a mini-split is 1/3 the cost of heating with resistance heat.

I live in a 2x4 framed ~2400' bungalow of 1920s vintage with a (now insulated) ~1500' basement that never drops below 65F in winter, with the original double-hungs +clear storms. Most of it is cathedral ceilings with 6" rafters and 4-5" of rock wool. After dense packing 90% of the wall area with cellulose improving the air tightness of the place it's heat load at 0F is currently about 35-36K. As I follow through on the intermediate & long term plans will bring it under 30K after some window upgrades, R20 rigid foam over the roof deck when I re-roof, and fixing the major gaps in the wall insulation. At it's current modified ( more open than original) floor plan I could heat this place as-is easily with a 1.5-2 ton mini-split on the first floor and a 3/4 ton on the (much smaller) upstairs space (but since I'm on the gas grid there is no cost-imperative at current gas prices.)

In new construction it's not tough to get the total heat load of a 2800' down to under 25K. Key to making it work with ductless is the openness of the floor plan and keeping the room load of the doored off rooms low. In a rectangular footprint two story it's dead-easy in fact. (Due to the lower exterior surface to floor area ratio.) But a mostly rectangular 2800' rancher isn't bad either. Using the simple footprint single story as an example, a "typical" code-min single story home that size will come in at about 12BTU/hr per square foot of conditioned space @ 0F, or about 33-35K. (Garfield county is a mix of US climate zone 4-5, you're definitely in the zone-5 part. Your code min's are probably what is listed for Garfield county here: http://energycode.pnl.gov/EnergyCodeReqs/?state=Colorado

If you design the roof trusses to be able to manage R75 cellulose (~18" "energy heel" ), and keep the east/north/west window area well bounded. That would cut the heat loss out the attic by about half, assuming you are religious about air sealing the ceiling plane (no recessed lights, foam sealing all electrical & plumbing penetrations, sheet-metal air barriers at all flue penetrations, sealed with furnace cement, etc.)

A code-min wall for you is probably R20 cavity fill in 2x6 framing, which comes in at about R13-14 whole-wall after accounting for the thermal bridging of the studs/plates/headers. Adding 2" of rigid Type-II EPS (R8.4) between the sheathing and siding would be sufficient for dew-point control at the sheathing (no interior vapor barrier necessary), and would raise the whole-wall R to about R21-22 (more than a 35% reduction in heat loss through walls). At 0F outdoor temps the R-value of EPS on the exterior will be about R9.5, so from a peak heat-load point of view it's even better than the average. Installing rigid foam without excess thermal bridging from the siding nails means fixing it in place with 1x furring through-screwed to the studs 24" o.c. and attaching the siding to the furring with ring-shank nails (necessary for retention with only 3/4" of wood to bite into.) With furring & fasteners, scrap rates plus installation labor it's about a buck-fifty, at most two bucks a square foot of additional cost.

A code-max window is probably U0.35- it won't break the bank to drop back to U-0.25-0.28 on the east/north/west windows, and U0.30-0.32 high solar gain (SHGC over 40) on the south side. And since you're minimizing total window area on three sides you'll have a net reduction over typical code min homes of about 30%.

Poured concrete foundation walls (stem-wall or full basement) can be insulated easily by using insulating concrete forms, which is often the cheapest solution in high labor cost areas. Under any crawlspace rat-slab or full basement slab putting 2" of Type-II EPS makes long term financial sense, and makes the space far less mold-prone (not that mold is as big an issue in your climate than in more humid climates.) A code-min floor is probably R30 between joists over an uninsulated crawl/basement, but with thermal bridging of the joists and the much greater floor area than the amount of above-grade foundation exposure, insulating the foundation is a far superior solution. R10 foam on the foundation would meet code min- the cheapest ICFs out there start at R16 (R20-22 is more typical.) But putting 3" of EPS (R12.6) on the inside of the stem-wall of a slab-on grade and "floating the slab works fine, as does 1" of EPS between a non-structural 2x4 batt-insulated studwall for a full basement. If you do the latter put 1.5-2" of EPS between the slab-edge and the foundation wall as a thermal break, and float the slab. Since the studwall isn't structural, it doesn't matter that it's cantilevered off the slab a bit.

At that point you'll be at least 30% under the typical 12 BTU/foot heat load, and well within the -5F output of a pair of 1-ton mini-splits, or a single 2-ton, provided you've air sealed it all adequately.

But there are other ways to get there. Double studwalls with cellulose make sense if you're looking at R40 whole-wall as a goal- it adds quite a bit of complexity to the window framing. An R30 wall can be had with 2x4/R13 plus 3.5" of exterior rigid polyiso at about the same wall thickness as the 2" EPS on 2x6 framing solution.

The crummy R12 refrigerant on/off reciprocating compressor heat pumps of the 1970s really crapped out fast below 30F outdoor temps. R22 and R410A refrigerant heat pumps of the '80s/'90s did better, but ductless mini-splits are in an entirely different class. Mini-splits and better class ducted heat pumps use variable speed scroll compressors & blowers, and are controlled to modulate speed with the load. Unlike on/off compressors that lose efficiency to abandoned heat and startup losses when operating at part load, the variable speed compressors' efficiency SOARS at part load, since both the blower resistance at the coils increases a function of the cube (third-power) of the air speed, and the surface are of the coils are large compared to the heat transfer rate, which helps quite a bit. Take a peek at the output capacity and part load efficiency curves in the bench testing reports of these two popular 1-tons (study figures 3 thought 8):

http://www.nrel.gov/docs/fy11osti/52175.pdf

In the NEEA Ductless heat pump program field monitoring the Eastern Idaho cluster in the Idaho Falls area (a climate about as cold as yours) was ten separate installations of 1-ton Mitsubishis. The field-tested average COP of the cluster came in just under 3.0, which is getting close to geothermal heat pump efficiency. Depending on what wood pellets and electricity costs in your neighborhood, it's highly likely that it would be cheaper to heat with mini-splits than with pellets. The whole document is probably a bit much for one quick read, but take a peek at the post-dated appendix discussion of the Eastern Idaho cluster performance- it's a good indication of the performance you can expect. (See Table 12 on p.18 of the Appendix, p138 of the .pdf pagination.)

http://neea.org/docs/reports/ductless-heat-pump-impact-process-evaluation-field-metering-report.pdf?sfvrsn=18

See also this short policy discussion with comparative lifecycle costs of different fuels.  Pellet costs vary by region and seasonal demand- New England has a fairly active timber industry, with quite a bit of pellet feedstock- not sure how it compares to your part of CO. But according to figure 2 the lifecycle cost of heating with pellets is about 50% higher than with ductless air source heat pumps, even if you subtract out the capital cost from their numbers, and look at JUST the operating costs:

http://www.rmi.org/cms/Download...+Northeast

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Bob and Dana
The question about ductless or single head per floor keeps coming up.
Both of you indicate that this is quite doable and I believe you have proven it in your own construction.

What happens when the design temps drop? It seems to me you both have reasonably high design temps and not too high wind exposures.

With higher delta, each room has higher heat loss and the distance from the head would become more problematic would it not?

As long as you are using the minis in moderate climes, one head appears to work. As the minis become more efficient such that they are being used in colder climes, are you sure the one head deal will work??

My 99% outside design temp and average winter temp is less than 10F warmer than yours. Many people in New England are heating with mini-splits in locations with design temps lower than yours. (A 65F delta-T between indoor and outdoor temps is only ~10% less heat load than a 72F delta.) I'm not sure how "moderate" Worcester MA (the location of the deep energy retrofit project house) is- it gets into negative single digits F at least once most years, and negative double digits at least once every 25 years. It's not significantly more temperate than Carbondale.

Both the Mitsubishi & Fujitsu cold-temp units have specified output at -15F- it's completely possible to size them correctly for your location.

In a moderately high-R house not a distance from the mini-split head issue so much as it is the conducted heat loss from the doored off room and the R-value & surface area of the partition walls between the actively heated common area. With any point-source heating its important to pay attention to that. With an R20-25 whole wall and an R2 partition wall it's the window losses that make it or break it on comfort when it's -10F outside. In the deep energy retrofit project housethe walls are closer to R40, and the windows in the doored off rooms were about 11 square feet of U-0.18. At a 70F delta-T the window loss is 70F x 11' x U0.18= 140BTU/hr, which is 100BTU/hr less than the BTU output of one sleeping human. With R2 partition roughly the same size as the R40 exterior wall, the room is 2/42 of the total-R between the fully heated space and the outside, so at a 70F delta-T it runs about 2/42 x 70F= 3.3F colder than the full heated space if there is no heat source other than one sleeping human in that room. The HRV system is set up with exhaust-only registers in the bedrooms, with ventilation air served to those room via jump ducts into the common space, so even that 3F max is tempered somewhat in practice, and it wouldn't be a crime to bump the temp on the mini-split up to 72-73 before heading to bed if it's going to be sub-zero overnight.

If it were only ~R25 whole-wall and an 11 foot window the temperature delta would be about 2/27 x 70F= 5F, still not insane. Even on that one day a century when it hit's -20F in Carbondale that's a 90F delta for a 70F room- a sleeping human still covers the window loss, and the bedroom might be 90F x 2/27= 6.7 F cooler than the common area, but you might be inclined to keep the door open on that night.

But if you make the windows in the doored off rooms 40 square feet of code-max U-0.35 you'r'e kinda screwed, unless you install an electric cove heater or baseboard to cover it when the door is closed. Like I said, it's the room losses, primarily the windows that make it or break it for the doored off rooms. (Going with casement windows allows you to go even lower in window size and still meet bedroom egress area requirements, but at some point the daylighting factor gets to be a bit of an issue. But up to 20 square feet of triple-pane can usually work just fine for a 1-person bedroom, 30 for the master bedroom. If you go with U0.30 windows you'll have to hold the line at about 10 square feet.

With remote rooms and point-source heating it's the same model whether you're heating with a mini-split or a wood stove or something else. Open floor plans tend to work a lot better than something with a Great Room on one end of the house, with a hallway with a bunch of doored off rooms, though that can sometimes be managed with a second head located at the far end of the hall, and another in the Great Room. There are high-efficiency variable speed ducted solutions (eg Carrier GreenSpeed), but they don't have the sub-zero capacity of the cold-climate ductless mini-splits- installing them in areas with design temps much below +10F gets iffy (though it's been done.)

Dana, Can I ask, what do you do for a living? You seem to be incredibly knowledgeable about this subject. Looks like I am going to go with a mini-split. Now the question is just how the configuration will be. Oh also just to give you a little more detail, the home is not an ideal solar home. The living space is 65% aligned on the east and west axis and 35% aligned to the north and south. However the 35% is on top of a garage (roughly 40 long by 28 deep) with about 1000 sq .feet of living area above it. The home also grew a little in the last design to about 2950 sq. ft. The east to west axis section on the home has good solar gain available with about 300 sq. ft. of windows for a livable footage of about 1850sq. So that should be decent for the gain, but not ideal. It is also a single level with a fairly open floor plan that is on ground level, while the other section above the garage is not, it is more of a traditional hallway/room configuration.

Just reading thru this thread and commenting on points as I come to them:

You mentioned no can lighting, I got to have some if possible. I like them and my wife loves them. We don't have to have a hundred though. They can be fairly well insulated though I thought?

Dana also keep in mind that when I say Carbondale, that is the town that is close to me, however I am 700 feet higher up and also exposed to much more wind. I am going to guess that that is probably the biggest difference. I am guessing that the temps are easily 2-3 degrees cooler up there than in town in Carbondale typically.

On the foundation, we will have a typical slab in the garage and then a 3-4 foot high crawl space on stem wall for the south( or lower) section of the house.

I guess one point I am not clear on here is why the mini splits don't operate well in a ducted system? I understand you lose heat in a ducted system, is that why? Or is it just the typical configuration of the heat exchanger in the type models you have talked about that are not designed for ducts?

if you have can lights, you must cover them with an insulated airtight box where the sides are far enough away from the fixture to eliminate the potential for the fixture overheating. That box must be tightly sealed, preferably with tape, to the top of the drywall. Then you need to make sure your attic insulation covers them thoroughly.

Oh another thing I forgot to mention, it can and does get colder here then what you might think by looking at the charts. We just got done with 10 days of weather that never got above 20 during early December. It hit -13 here on one night and 4 or 5 other nights it was 5 to 10 below zero as well. Last year I saw -17 up here. I think the record in town is -38F. That is about unheard of, but -10 to -15 is not that uncommon at all. And then of course we can have the flip flop of that where it is super bright and sunny and 45 degrees during the day in January as well for maybe a week when a good high pressure builds in. The swings we get in our temps I think are probably more severe than the east coast due to , at least in part to the lack of humidity.

I make my living as electrical engineer (analog electronic)- the building science and energy efficiency stuff is mostly a hobby, though I get pretty deep into the weeds with it on family & friends' projects sometimes.

If the can-lights are low-profile completely air-tight LED types with >R50 above them, it's not going to be an issue. Absolutely air tight is key, not kinda-tight IC (insulation contact) rated cheapies from the box store.  If the latter, the only option is to box over them, sealing the box to the gypsum with can foam & caulk.

With 700 of elevation you're looking at about a 2F adiabtic temperature delta, maybe a hair more on higher humidity days when the radiational cooling in town is a bit lower.  So if the 99% design temp for Carbondale is something like -2F, figure on -4F or so as your design temp.

Being on a windswept hill makes air-sealing more critical than it would be in house in a high density neighborhood in town, but if you can get it under 1000cfm/50 the effect of the wind on your total heat load is near zero, since multiplying a nuthin' infiltration rate by five is still nuthin'.

I totally get that the diurnal temperature swings are much higher in Carbondale CO than Worcester MA due to the radiational cooling, but I also get that it works both ways. Carbondale is the cool edge of zone 5, Worcester is the middle, so the averages are comparable even if the differences between the seasonal low temps are a bit wider.  We too get cold snaps where it doesn't break 20F for several days, but when it hits -10F here the high for the day is typically about +5F, whereas a -10F night in Carbondale is followed by a day that hits +15F or even higher. Case in point- a coupla weeks ago it hit -11F at 3AM in Carbondale but was up to +10F by 10AM, and +27F at 3PM, December 5th was similar, bottoming out at -11F at 6AM, but up to +23 by 1PM: http://weatherspark.com/#!dashboard;a=USA/CO/Carbondale 

But the total number of hours spent below -10F in Carbondale per season are few, and the number of days where it's below -10F for more than 5 hours in a row even fewer.  Temps rise quickly after dawn, which is why a 99% outside design temp (and not the absolute low temp) is the proper temp to design for- it takes a sustained period below the 99% bin temp for the house to actually get cold.

Even when the heating plant is sized EXACTLY for the 99% outside design temp, a handful of hours 10F below the design temp doesn't pull the temp of the house down by very much. The higher the R-value of the house, the less ground it loses too, since there is quite a bit of energy stored in the thermal mass inside.  The decay rate when the heating system isn't keeping up is very analogous to a resistive discharge of a capacitor where the average R-value is the resistance, and the thermal mass is the capacitance.  If a code-min house would initially lose 1F per hour with a 10,000 BTU/hr shortfall from the heating plant, an R40 wall would lose about 0.3 F per hour, so cruising through 5-6 successive hours of temps well below the 99% design temp is hardly noticed in the high-R house, whereas you could be pretty chilled in the AM with a code-mid house.  Most heating systems are oversized by more than 10% anyway, and the difference in heat load between -5F (a 75F delta-T from a 70F room) and -15F (an 85F delta) is only  ~13%.  On a low-load high-R home the difference is more than made up if you left the 52" TV and game system on overnight.

The duct impedance takes more blower power than a mini-split head at higher cfm rates which give is a lower coefficient of performance. There are mini-duct heads for ductless systems that work pretty well if you keep the duct runs short, and you can split the output between 2, sometimes 3 rooms with them.  But the cold-weather mini-splits most appropriate for your climate work most-efficiency with the wall-blob heads.

BTW: You might find this bit o' bloggery  about a double-studwall house in an even colder climate of interest. He's claiming the cost uptick for the whole high-R shebang (windows included) was about 7% of the construction cost.  Building high-performance buildings is more about a thoughtful design than an engorged wallet.  This Passive House with ridiculously over-R walls (he liked the round number of R100- it didn't really need that to meet the energy use spec) is located about 5 crow miles from mine, and heated with an oversized Mitsubishi 2-head multi-split, that they run in air conditioning mode sometimes even in winter.  As I said, temps of -5F to -10F aren't super-rare here, even though the 99% design temps are typically between 0 and +5F.  Another local builder has built a whole development of Net Zero Energy houses heated with 1-2 mini-splits and ~8kwh PV array, in a location with a 0F design temp.  These are a bit smaller and a bit boxier than you probably have in mind, but they also get far less passive & PV solar input.

Well you are right on target there Dana, yes our swings back in December where actually more than I remember. Colder at night than I thought and a bit warmer during the day than I remember. Well it appears that you have a very good understanding of the temps here. I guess one thing maybe I missed was , what would be the design temp here? I think you already said, but I maybe missed it.

Also, what do you think about the "not so great " layout of the house as I have described it? I am fearful that I am going to be losing quite a bit of potential efficiency in the name of architectural design...... you know how that goes. And actually it was not that much about looks, it was about cost and sizing on the lot. I ran out of room, without going into a rocky outcropping that would require blasting or jack hammering. So the thought was to go above the garage where the space would be "cheap."

Also, if for some reason you may be inclined to look at my schematic drawings, maybe I could email something to you so you could better understand the layout?

Could you elaborate on the down falls on the ducted system on the mini? I am following you some of it, but still not totally clear on exactly what you mean. The single source head concerns me due to dual, long and skinny layout of the house. Remembering that the house is a long skinny L shape, basically from one far end of the house to the other is about 105'. I guess you could locate one head on the upper level on the far side and the other head on the ground/main level on the opposing side but still (traditionally thinking here) seems maybe shy. This whole concept is extremely new to me and I guess I am not yet up to speed on exactly how these work and placement. Just cant get ducts out of my head))))

thanks a million Dana!

You mentioned no can lighting, I got to have some if possible.

Don't do it. You will be sorry over all those gaping holes in your otherwise lovely shell. We ultimately got quite a few cans in by using them only under second floor living space. They don't matter at all when used there. We also dropped ceilings during construction in a number of places where we just didn't have to see the whole lofted height and then proceeded to use the spaces over as storage and mechanical. That worked quite well. In the remaining spaces, we used Juno LED Trac 12 lighting which utilizes a remote transformer (often mounted in those newly created storage spaces), low voltage wire in the rafters and tracks for LED lighting, including pendants. It's not cheap, but the results are very nice.

Getting a multi head system isn't the end of the world if you are worried about losses in a far flung bedroom. I have a four head Daikin system, putting one head in a large media room (primarily for air conditioning) another in a guest bedroom that has a lot of sun exposure( again, air conditioning being the primary aim), one head in a Master bedroom that is a little removed from the main airflow thinking of both excess sun exposure from the westerly window and excess heat loss, also due to the window, and the last in a bedroom that is out on a corner with huge North windows.

Yea I figured covering all those cans could be a big pain. I appreciate your input on what you used. Sounds like maybe that is a route to go. thanks

Sounds like maybe that is a route to go. thanks

If you want some other pointers on what I learned, be sure to take it to the "Lighting" section below and I will be glad to tell you some of the things I learned about lighting during this project.

Sure thing, again thanks for the candid info. A question for you. How does your ducted, four head mini compare to the ones that Dana were talking about? I like the AC capabilities of the units, but the big thing for me is the heating side of it, as I would only use the AC side for about 8 or 9 weeks. The heating side of it, now that's a different story. We need heat for 6 plus months of the year. I got to be sure that what I put in is going to be sufficient for almost all of my heating needs if I decide to rely solely on the minis. It is also evident that if I go that route, I am also going to have to be very careful on the insulation and sealing of the house. If I didn't buy that pellet furnace and the associated duct work, then it would free up quite a bit of money for insulation. Maybe I am being to optimistic. Anyway, would be curious to know the output of your unit with the ducts at say 0 degrees. Also, if the temps go up to say 15 or 20, how much more does that add to your output of the mini? Oh one major "potential" heat source I forgot to mention initially, was a planned pellet stove located far to one side of the house in the great room where my wife just HAS to have some kind of stove. I fought like hell to convince her that pellet instead of wood was the way to go, I just cant bare working up wood now due to health issues that she still doesn't quite understand. However, I don't want to use or rely a pellet stove at high output to heat part of the house due to noise.

ps. Thanks for the info on the lighting, I have not go there though quite yet. But I will for sure fairly soon. One thing I had in mind was that I was hoping to do mostly LED with maybe some CFL to help on costs.

I have a Daikin mini split system which was selected for quality, features and efficiency. In heating mode, it will produce about half of rated capacity down at 0F, according to the Daikin engineers. That is a temperature we never see here. Our design temperatures are down in the teens and the Daikin unit has nearly full rated output in those temperatures.

If you are going for low temperature performance, you will want to look at units from other manufacturers such as Mitsubishi and Fujitsu. They can produce nearly full output at 0F and 70% of full output down into the minus teens, I believe.

I believe that pairing a ductless mini with a solid fuel burner is a natural match. I will always have a wood burner of some kind because we enjoy the visual aspects of it. We have a fire going nearly full time from November thru February or March because we enjoy it. That extra heat capacity allows a homeowner to size his regular heating system more modestly, rather than having to plan for the coldest lows.

I have had pellet stoves, but I am not a fan. For some reason, the care and feeding of a pellet stove seems to be twice that of wood. Probably just perception because we live in the Pacific Northwest. I have 5 cords cut, stacked and seasoned, and another 10 cords in logs, if need be. Pellet fuel requires a functional distribution system, but the wood will always be available to me.

If you are going to have a solid fuel burner of some kind, and you plan to use it a lot, make sure you get it with remote distribution, or the ability to send some of the heat remotely using a duct and fan. This should be done with your home's natural airflows in mind.

I am also going to have to be very careful on the insulation and sealing of the house

That is important, no matter what else you do.

I expect the 99th percentile temperature bin for a place 700' up above Carbondale to be somewhere around -5F, not much colder. The 99% outside design temp for Leadville is -14F, but they have about 3500' of altitude on you, so they'll be about 10F cooler on average, all else being equal.  The 99% bin for Eagle CO is -7F, which is closer and about the same elevation, so your 99% bin might be the same, but probably no colder.

Duct impedance has a significant impact on net efficiency. Some of the low-temp Mitsubishi "Hyper Heating" units are compatible with SOME of their mini-duct cassettes, but I suspect both the capacity and efficiency at -25C/13F (the coolest temp at which is has a specified-guaranteed output figure) is probably much lower than the wall-wort versions.  I wouldn't take any installers word on the cold temperature performance of a mini-ducted unit without getting it straight from the folks at Mitsubishi. Mitsubishi has a huge catalog of cassette options, some of which can hook up, but aren't fully compatible, so be careful when straying from the most-conventional pairings.  I'm pretty sure the Fujitsu RLS2-H series is only compatible with the ASU-xxRLS2 heads, and not any of their mini-duct cassettes.

Well Dana, sounds like I am going to be better off installing quite a few wall mount units. Maybe of several different sizes. That could get pricey potentially though. I just want to make for damn certain that what I am putting in is going to be sufficient and I am not cutting holes in the walls later trying to add something that could have been a lot easier on the upfront side.

Also, maybe I missed it when I was glancing around at the Mitsibus site, but do you know if they or another company offers one of these "hyper" series with say two heads you could mount inside versus one? While they would not be ducted units, they would however be splitting the heat between the two heads maybe 35-50 feet apart.

I say this because I guess I still can't quite get comfortable with the idea of heating with a single point source of heat, especially for a L shaped, split level house that is not really setup to heat from a single source location, like what I grew up with as a kid where the house was a single level rectangle with a full unfinished basement to match the footprint and a huge wood stove in the dead center in the basement that heated the entire upstairs floor because of its central location and some duct work with a blower. I realize that this late 1970's house probably had a 10% efficiency rating compared to the home I am proposing to build, but the concept is still the same. Heat moves from hot to cold areas, but with multiple layers of walls in the way, some of which will be insulated for sound, it concerns me. That is why I am asking about a dual head or ducted system. Sorry to sound repetitive.