Looking to build an R5-10-20-40-60 (or close) 26x32 2-story home in VT  this summer or next Spring.
Propane is around $2-2.50 per gallon and electric is $0.17 KWH.


With budget being a concern, my question is whether a centrally located (first floor living room which is open to kitchen/dining) 38k BTU Rinnai 1004 will comfortably heat a 2-story home.   From a heat load perspective, it will theoretically cover it.  Whether the heat will effectively and comfortably "reach" the whole house is another question.  With that being said,  we do not mind the bedrooms (upstairs) being slightly colder than the 1st floor.

To supplement bathrooms, we could add in-floor electric radiant or electric heat.
For domestic hot water, we could use either: tankless, a .80+ EF propane tanked heater or hybrid electric tank heater, all around the same price range ($1300 for unit plus install)

A high efficiency  baseboard HWH system  is an option but I think we can net more by spending more on the insulation values and cut back on the heating and hot water system.

Wisdom Way Solar Village (Rural Development Inc) does basically just this for their heating, although the home is slightly smaller (1400 sq ft), their unit is a Monitor, not a Rinnai , which may (or may not) work better.

Any thoughts, or other ideas that might work?

Heating and cooling this home with Mitsubishi "hyperheat" minisplit air source heat pumps will be your least expensive - and best - option by far - both to install and to use. One or two* down, one up, at +/- 3000-3500 each to buy and install. (one will probably do the first floor, but depending on the layout you might want a second) These are 3X the efficiency of the best fossil fuel or electric resistance heaters. By next year they will have an exterior unit that will run three indoor units so the cost may be even less. These are being used by practically all of the best high performance builders in the area - good quality, quiet, and inexpensive. I've put them in several homes and just ordered some for my old house. Add a PV system and never pay for electricity or heat.

Increase the insulation under and inside of your foundation from those guidelines, make it very, very airtight, install an HRV. There are many good HP builders all over Vermont - you can check put the NESEA website list of builders for ones in your area.

First the room-by-room heat load, then the mechanical systems. From the information I like a Marathon electric and heat pumps if the fit the Architecture. Radiating bathroom floors with electric as Jonr often promotes is a good idea and may heat and humidify the whole house a good part of the year.

Posted By Bob I on 14 May 2014 06:09 PM
Heating and cooling this home with Mitsubishi "hyperheat" minisplit air source heat pumps will be your least expensive - and best - option by far - both to install and to use. One or two* down, one up, at +/- 3000-3500 each to buy and install. (one will probably do the first floor, but depending on the layout you might want a second) These are 3X the efficiency of the best fossil fuel or electric resistance heaters. By next year they will have an exterior unit that will run three indoor units so the cost may be even less. These are being used by practically all of the best high performance builders in the area - good quality, quiet, and inexpensive. I've put them in several homes and just ordered some for my old house. Add a PV system and never pay for electricity or heat.

Increase the insulation under and inside of your foundation from those guidelines, make it very, very airtight, install an HRV. There are many good HP builders all over Vermont - you can check put the NESEA website list of builders for ones in your area.

Thanks. I will look into these. My concern with the air source heat pumps is regarding the performance at low temps. It was a very cold winter this year. I will have to dig up stats on just how cold it really was.

Is there an easy way to compare heat pump to propane cost , assuming I know approx how many gallons of propane I will burn. For example 600 (this is an arbitrary number) gallons of propane = ~ 55500000 btus = 16265 kwh. Is it actually safe to assume that a heat pump will create 16265 KWH of heat energy by only using 1/3 of that in electricity: 5421 KW/H at .17 per KWH would be $921 a year.   600 gallons of propane could be anywhere from $1200-$1500.   This would assume it's getting a 3x coefficient of performance all the time, which I do not think would be the case in cold temps.

HRV is a definite on the to do list. We'll investigate more insulation as well!

The Mitsubishi Hyper Heat system puts out 100% of the rated BTU down to 5deg F. The 9000btu system I am going to buy is rated for 10,000btus down to 5deg F. You will still get usable heat below that.

What is the lows in your area?

It's USDA Zone 4B - they say -20 to -25 F. , I think I saw -18 F this winter a few times. but we often realistically see -5 F+. I will get some better stats , like number of days below 0 or -5F.

At -5 F you are still looking at it producing 90% of its rated capacity. I would check with mitsubishi at what temp the thing cuts out completely but if I remember correctly they run pretty low. You could probably get away with some supplemental electric heat or a secondary gas fired device that you would not use most of the time.

My current HVAC system struggled a bit this year because it got a lot colder than it did when I put them in. Due to the efficiency of each 2 ton unit they were putting out about 3/4 ton without strip heat. I dont think my stat handles strip heat use right so we would drop a small electric space heater in our bedroom some nights. That alone picked up the slack and made our entire second floor just warm enough so that the heat pump did not stay on constantly during the night. Without it on a 5deg night the stat would stay set at 68 and get to about 63-66 just before dawn at its coldest point.

Realisticly, with high propane and high electric costs, you want to use anything with a COP to heat your home or hot water (geo or airsource).

I just looked at stats for 2013/2014 winter and we had:

60 days with min temps below 5F.
15 days where the avg temp is below 5F.
1 day where the max temp is below 5F.

So minisplits are ideal; especially combined with PV. There are several articles in Fine Homebuilding, Journal of Light Construction & greenbuildingadvisor.com about these & some about how they've worked through this past winter. Worth reading.

Cool... EFficiency Vermont is also pushing these. I don't think I can generate enough electric on our small roof to be "net zero" but will look into it further.

Honestly , these are cheap enough that I could install a Rinnai direct vent propane heater below the mini-split at the same location, for backup or very cold days.

Install one that runs without electricity so you can use it during power outages; otherwise you'll never use it. Ground mount systems are better in some ways; PV doesn't have to be on the roof.

The new "M-series" Mitsubishi ( MSZ/MUZ-FHxxNA ) mini-splits put out 80% of the full rated output at -25C/-13F, and keep on chugging at some unspecified output for 10s of degrees below that. The 3/4 ton unig (-FH09NA) is rated for 10,900 BTU/hr @ +5F, and would still be good for about 8800 BTU/hr @ -13F. The 1.25-tonner (-FH15NA) is good for 18,000 BTU/hr @ +5F, and about 14,500 BTU/hr @ -13F. The 1-ton is rated 13,600 @ +5F, and still delivers about 11,000 BTU/hr @ -13F.

http://www.mitsubishipro.com/media/946493/fh_product_guide.pdf

It's typical to put one head per floor on 2-story homes, which has the advantage of being able to use convection for cooling during the summertime peaks, running primarily the upper-floor unit, and conversely during the heating season.

The 99% outside design temps in VT are all warmer than -13F, except possibly at higher elevation ski areas or something. If you size the thing to cover your 99% heat load (calculate it), it'll have sufficient margin for when it hit's -20F or cooler.

http://www.mitsubishipro.com/media/946493/fh_product_guide.pdf

At -13F outdoors these things deliver a coefficient of performance (COP) of about 2.0, or about 6800 BTU/kwh, but at your wintertime average temps you'll be looking at an average COP of about 3.0 over the entire heating season, or about 10,000BTU/kwh. That means your heating will take 100 kwh/MMBTU (that's per million BTU), at a cost of $17/MMBTU. When it's averaging -10F outside it'll be more like $25/MMBTU, but when it's average 35F out it'll be about $13/MMBTU . Your worst-possible case average would be $20/MMBTU averaged over the season, and then only if it's the coldest winter on record. Best-guess typical would be ~$16-18/MMBTU with a series-M mini-split.

Propane has about 91,500 BTU/gallon, and even burned in a 95% condensing burner delivers only 87,000BTU/gallon. That's 11.5 gallons/MMBTU. At your best-case $2/gallon propane that's $23/MMBTU. But in an 82-84% heater like a Rinnai 1004 it's more like $26/MMBTU, best-case, and at $2.50/gallon it'll be $32/MMBTU, or about twice the operating cost of the mini-split solution.

The Fujitsu XLTH series is very similar to the series M Mitsubishi units, with modestly lower efficiency numbers, but it would still bury any propane-fired solution on operating cost: http://smartgreenbuild.com/pdf/Fujitsu-RLS2H.pdf

A tight ~1700' R5-10-20-40-60 house will likely come in between 15,000-25,000 BTU/hr @-10F depending on just how tight it is and how much window area you have. A pair of 1-tons ( one per floor) would almost surely get you there, but might be overkill. It's important to get it right, and size accordingly. If it's oversized by more than 50% efficiency will slip a bit due to cycling and standby during the shoulder seasons. Sized right they should run almost constantly (almost always at the lowest speed) from late-October through mid-April, and won't lose much ground (if any) during cold snaps.

In snowy VT it's important to mount the thing where it won't get buried in snowdrift or get bashed/buried by roof-avalanches & cornice-falls. Bracket mounting it on the wall above the anticipated max snowpack depth, protected by the overhanging rake (better than eaves) of a gabled roof means you end up doing a lot less digging to stay warm. The purpose-made brackets for wall-mounted mini-split compressor units, is really the right way to go in your neck of the woods.

thanks for the analysis. Very interesting!

Dana has you covered pretty well here. Just a couple of points-
1. You will definitely want an HRV and as tight a shell as you can get.
2. I would consider an electric heater in the bathroom- on a timer in floor heating is nice.
3. You will have cooler rooms if they are doored off. The better insulated the shell the lower the internal temp differences are. You are counting on the fact that the exterior insulation is much greater that the room to room insulation. Where you end up in trouble is if you use sound control insulation in the interior walls. This can cause cold rooms by retarding heat flow through the interior of the house. I bring this up because if you have kids, sound insulation can be a nice thing.
4. IF you were going propane, I would probably go with a combi-boiler + baseboard so I minimized costs for hot water also. IF you can get your load low enough that a single 1000 gallon tank of propane lasts a year or more than you can fill when propane is cheap- in the summer usually. This helps, although the minisplit is going to be cheaper overall.
5. Making sure the house is oriented correctly to have a roofline amenable to solar PV or thermal makes sense. When PV gets under 2$/watt it is going to be a no brainer.
6. Windows specified and oriented for winter solar gain, with overhangs to prevent summer overheating.
7. Consider using www.yoursolarhome.com solar air collectors, wall mount them on the south wall. The advantage of these over high solar gain windows is that they can be thermostatically controlled. You don’t need to worry about overhangs because in the summer with the fan off and the damper closed, there is not that much heat transfer.
8. Basically I look at it this way, great insulation and airsealing cuts your heat loss dramatically, carefully done, solar can easily account for ½ the remaining heat required if it is designed in from the start.

I just priced out a home in Arlington VT with 8" eps walls and 4" concrete core. I was suprised that the the icf came in at $3.10 per sq ft plus shipping

What are people doing for Domestic HWH when they are using air source heat pumps to condition home? Heat pump tanked heater like GE GeoSpring?

yes. Mitsubishi will have a model out shortly which will work with a minisplit compressor. Basically the refrigeration line from the outside compressor will go through the hot water tank on it's way to the minisplit.

Another question... what, if anything are people with all electric mechanical systems doing for backup power?

Having gone through 1 week w/o power in NJ, two years in a row (granted this has not happened in VT, but it could) , a LP generator has been on my "want" list.

With the FE18 pulling max. 2,420 W to heat, it is possible we could still run off the smallest Generac Guardian (8000 watts) , leaving 5500 watts for pumps(would have to check wattage on these), refrigerator and lighting (just the basics). I know these things are the antithesis of efficiency, but will also not be used very often.

Posted By Bob I on 30 May 2014 10:19 AM
yes. Mitsubishi will have a model out shortly which will work with a minisplit compressor. Basically the refrigeration line from the outside compressor will go through the hot water tank on it's way to the minisplit.

very cool!  Sounds like we will be building after quite a few new , even more efficient products  come out.