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Looking for advice - Off Grid cabin in Utah - winter heat

Russted

New Member
Joined
Feb 12, 2020
Messages
15
We are starting construction documents on an off-grid cabin in in central Utah. Located at 7,200 feet in climate zone 5b, with a heating design temp of 15 F. Approx. 1,800 sq/ft, with open kitchen/living/loft area of approx. 1,100 and two smaller bedrooms. This will be used part time, but year-round. This will not be built to passive house standards, but we are aiming for Pretty Good House (or Almost Pretty good house.) Slab on grade. I’m also trying to avoid gas/propane as much as possible. We are not concerned about cooling at this location.

I’m looking for advice on winter heating. I was all set on Minisplits with propane generator to back-up charge my battery bank, but now I’m not sure if it’s the best option.

Goal: Keep the house at a consistent 40/50+ degrees all winter when not in use on minisplits (bumping up to 70ish and supplementing with wood stove when in use)

Solar:
405W x 36 = 14,580 Watt and approx. 23,588 kWh/year

Winter Production:
Nov – 1,902 kWh
Dec – 1,708 kWh
Jan – 1,978 kWh
Feb – 1,887 kWh

Energy:
- 64kWh battery bank
- Inverter TBD – Most Likely LF type
- Generator – TBD, but idea was to have a small propane based one for battery charging only.
- 80 gal HPWH
- Well Pump 1 ¾ - will eventually swap with either solar direct or Grundfos. Pumping to large cistern, so not as concerned about start-up. Will not pump much in the winter months.
- All other appliances will run off electricity

Minisplit Options:
  • 1 larger 12-18 sized system for the open area
  • 1 multiple split for the two bedrooms/bathrooms (may just go with 2 smaller 1:1 units, but seems like overkill for these rooms)
Questions/Concerns:
  • Can Minisplits be set to run at 40-50 F? I’m reading conflicting information. The Hyper Heats are intriguing, but if I have to run then at 60F, I’ll kill my batteries quickly.
  • I am running PEX for hydronic system under poured slab – was going to leave this stubbed but not connected. Now I’m wondering if a hydronic system might be more energy efficient than multiple minisplits in this specific low heat situation.
  • I just started research into hydronic systems and I’m having issues determining the most efficient solution to the challenge outlined with hydronic. It seems either an Air To Water Heat Pump or Electric Boiler would be the best options, but not much info out there to review.
  • Everything I’m reading says solar water collectors aren’t spec’d anymore. I am trying to avoid this option if I can.
I'd appreciate any advice I can get from this group! It's a remote area and the contractors we have spoken to do not have any experience with off-grid, so I'm trying to make sure we are going down the right path.
 
Definitely put insulated slab hydronic floor even if you don't use it right away. You can get hot water from wood fired boiler or ground source heat pump in the future. Place water heater in living space so that heat loss will not go wasted. You may not even need heat pump water heater but the tank with built in heat exchanger loop would be nice for different heat source options. Look into bathtub / shower drain heat recuperators.
 
Thank you... hopefully the PEX in slab will "future proof" my heating options. I'm looking into those heat recuperators as well.
 
Any time a generator is used during winter, I'd sure like to see Combined Heat and Power, get closer to 100% not 33% of energy in fuel.

64kWh bank can probably accept 32kW peak charge, so this doesn't have to be a small generator. I'm guessing anything between 5kW and 20kW would not be unreasonable. A 5kW generator running at 3kW charging load and delivering 6kW of waste heat to the house might be nice.

No idea the price. I see "5kW" in a picture, but only 35kW units described in detail.


The prices in here are not attractive


1kW



Maybe just DIY recovery of liquid-cooled and exhaust heat from a conventional generator.
 
As a fellow Utah also looking at off grid property…

Get Propane as a backup - even if you get several 100# - 25 gallon tanks that you take to someplace for refills (if there isn’t a good propane delivery company in your area.).

You will get snow on the panels and if you are not there to knock the snow off - your solar will drop drastically.

Look into a propane boiler for your slab heat (with an electric backup). That will be more efficient than running the generator to make power to store in the battery to use in an electric boiler. Or the propane is the backup to the electric.

Is your property all various sizes of rock or do you have an option to put in ground loops of pipe for geothermal heating/cooling? This is the most energy efficient method of heating/cooling.

Good Luck
 
Thanks for the great feedback, and I agree with this... "Off grid in winter, you need backup on your backup for heat." Based on what I'm hearing, I should be researching propane in more detail as the primary. You've also opened my eyes to "waste heat" so I'll dig into that from the generator. We can get propane to the site, so it's an option. I

Jackson - My thought behind keeping the cabin at 40/50 F in the winter: We would be using it randomly in the winter. I didn't want to have to winterize it every time we leave, and then bring it back up to temp when we arrive. If winterizing is as easy as making sure the plumbing all flows to a low point to dump water from the lines, maybe I'm making this more complicated than it needs to be.

Chispas - Based on our initial interviews with the contractors in the area, none of them had built a passive house, and I got the sense they were not excited about learning. We have another round of follow-up, so I'll dig into this one a bit more. The builders are familiar with high levels of insulation, so I'm taking what I can get with the limited experience in the area.
 
Heating is a lifetime of expense, so anything you can do now to reduce that will pay you back in spades. Propane is cheap - for the moment, but I remember my dad telling me how folks who oil fired heating in the 70s were screwed when the OPEC crisis quadrupled the cost overnight. Passive haus isn't rocket science, it's a set of design parameters & contractors who are not interested in doing something slightly different might not be the best chioce.
 
"Contractor" vs. "Architect"?

Contractor should be able to build according to architect's plans at least if conventional materials and construction.
Passive or other climate control methods would mostly be dimensions & geometry, materials & components, etc.
 
"Contractor" vs. "Architect"?

Good point. We contracted with the architect before I began to learn more about passive house construction and off-grid living in general. I have to blame myself more than anyone else in this regard. The architect has done projects in the area we are building, but none off grid, so they are familiar with the 2-3 building contractors in the area. It would have costed us more than I wanted to spend to start over on the building plans. They are familiar with "Pretty Good House," so we are aiming for that in regard to building envelope, sealing, glazing, etc.

I'm currently researching the following:
- Direct vent furnace (Thanks Wheelman)
- Propane boilers & Geothermal (Thanks Rocket) One of our neighbors has this, but he wasn't sure if the upfront cost was worth it in the long run, and the soil is rocky.
 
How much property do you own? Is it flat or mountains? Are you sure that you need to keep all 1700 sq feet at that temp? Is it in an protected area or an association? Does it happen to have a natural spring close by? Is it on pavement and insurable? How far do you live away in miles. Is there a caretaker in case you need one? Do you have connectivity year around? Do you have to stand inspections as for plumbing, electrical and other inspections as well as permits? Has your contractor done offgrid before?
Your descriptions so are that you are well into big money and that makes your ideas doable but complicated in many ways.
I'm asking because some of these questions enter into what we envision in our minds. I do have a DIY off-grid cabin at 9700' in the very remote Colorado. Small cabin with separate bunk house for guests along with garage and shop a quarter mile away. Don't want guest too close.
The only thing that stays power up during the nonuse season is a weather station with a few cameras and a hotspot for connectivity. Cabin uses a 300 ah now lithium 12 volt for lighting and an 3000 watt inverter for a few 120 Vac loads.
 
In addition to above questions, how much winter sun does your location enjoy? Passive solar could very well be your answer. Thoughtfully designed, your vacant energy costs could be zero. Comfort while occupied could be wood stove only when storms are rolling through, or to take morning chill away for the cold intolerant.

Our 7,200 feet elevation small home in central New Mexico USA does this. The separate, bedroom straw bale structure I built is without any supplemental heating for 3 winters now (I went through two direct vent propane heaters for the previous 27 years, using about 6, 5 gallon propane tanks a year; high altitude orifice is a must).

Yes the interior temperature has gone down to about 45°F a couple times. Usually it is in the 60’s at sunrise. Sunny winter days will offer mid 80’s warmth in the late afternoon; more if it is a warm spell when the sun is low. Opening windows is always an option. Abundant insulation applied astutely is money well spent.

EDIT: Credit Union that gave us a loan for the property required us to have a contractor-installed propane space heater. Other than testing, it simply is not used.

Don’t put plumbing in the north wall of your structure!
 
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Any chance of using a diesel heater? They are cheap and available. Some garages and shops of decent size use them pretty well.
 
Multiple heating sources sounds like a better approach with one of them being propane. Propane heating is a better option in that it can run in your absence without need for power so no demand on your winter time lack of solar production. This solves the issue of keeping the space above freezing without penalty to your battery bank when you’re not there to keep an eye on battery capacity. When you are on site and your battery capacity and solar array production favor it, you can switch to heat pump as your secondary.

Heating with electricity is not very efficient especially when running a propane backup generator to charge up a battery bank to then run a heat pump. That sounds less efficient than just using propane to heat the space directly. Using a heat pump seems to work best when you’re there to know that that you’ve got the excess solar capacity for it.

Another angle of attack would be to program your off-grid inverter to stop supplying power to your heat-pump at about 50% battery capacity (or some other % that seems right to you), then let the propane heater take over. Set the heat pump at say 50 degrees F and set the propane system to 45 degrees F. This way you take advantage of electricity when you have it and propane only when you need it for the times no one is on-site to fuss with systems.

My home is entirely off-grid but I get the issue of keeping a space above freezing when not on site. I have a small, 460 square foot guest house on another part of my property that I keep heated through the winter (coastal Pacific Northwest) with a small propane heater that vents to the outside. The propane heater can either use a pilot light or electric spark and has its own small 6 volt battery backup for the electric spark. I usually shut down power entirely to the guest house and let the battery backup control the spark for the propane heat and keep this space at 62 degrees in the winter. This temperature makes it easier to heat up when guests arrive on short notice and keeps the space dry to prevent mold issues but I could set it for lower.

A caution against direct-vent propane heating: Direct-vent propane systems vent all the combustion gasses into the living space and water vapor is a byproduct of propane combustion. Humid spaces soon become moldy spaces. Instead, use a propane heater that vents to the outside and also receives its combustion air from the outside so the inside space can be free of mold-feeding excess humidity. If I’m not mistaken, in some super cold, snow-belt areas, the air is actually quite dry so maybe excess humidity is not a winter issue for you; it is where I live.

In my case, I live full time at my off-grid home so I heat with wood in the winter though I have a propane, whole-house heating system as a backup to the wood stove. I’ve thought about a heat pump for air conditioning in the summer time when I have an excess of electricity from the solar array but since it only gets uncomfortably hot about 3 days out of the year and I have a cool basement I can sleep in for those times, I never installed a heat pump.

Good luck, sounds like a grand project.
 
Before I jump into this, I just wanted to say that I'm blown away by the help and ideas on my initial questions! It's great to know there are a bunch of people that have already gone down this path and are willing to share what they've learned.

Good questions Jhar which would probably help round out the info. Just over 20 acres, high desert, views to the North (unfortunately, as we will have some windows facing that direction.) We do not need to keep all 1,700 ft conditioned, obvious concern is kitchen, 2 bathrooms and mechanicals, which are not right next to each other, but pretty close. Water is from 300' well, septic for waste. It's insurable, county road to gravel driveway easement is access to site. We will building in fire mitigation with cistern and dry hydrant. We live 3 hours away without traffic. No caretaker, but we are meeting more people in the area, so we might have help close by if needed. No HOA. I was shocked to find fiber optics run last year up county road, so we will have connectivity. We will have inspections, but neither of our potential contractors have done anything off grid (which is really why I'm spending a ton of time research options.) We do realize it's going to cost us a bit more than we had initially thought, but we are OK with it. We were quoted $60K to tap into the grid... I hope I can figure most of this out for less than that amount. This is our dream location, and we've been saving for a long time.

From a sun perspective, we do get quite a bit. We have built in some passive solar ideas with s. facing clerestory windows. I'm just not sure how much those are going to impact my energy needs, so I'm trying to plan for the worst. I need to check with our architect and see if they can provide an energy audit based on the initial plans.

Yes the interior temperature has gone down to about 45°F a couple times. Usually it is in the 60’s at sunrise. Sunny winter days will offer mid 80’s warmth in the late afternoon; more if it is a warm spell when the sun is low. Opening windows is always an option. Abundant insulation applied astutely is money well spent.

Don’t put plumbing in the north wall of your structure!
Sounds fantastic, and thanks for the advice on avoiding plumbing in N. walls.

I will look at diesel heating as well, but since we had planning on having some propane, I'm running down that direction right now.

Another angle of attack would be to program your off-grid inverter to stop supplying power to your heat-pump at about 50% battery capacity (or some other % that seems right to you), then let the propane heater take over. Set the heat pump at say 50 degrees F and set the propane system to 45 degrees F. This way you take advantage of electricity when you have it and propane only when you need it for the times no one is on-site to fuss with systems.

My home is entirely off-grid but I get the issue of keeping a space above freezing when not on site. I have a small, 460 square foot guest house on another part of my property that I keep heated through the winter (coastal Pacific Northwest) with a small propane heater that vents to the outside. The propane heater can either use a pilot light or electric spark and has its own small 6 volt battery backup for the electric spark. I usually shut down power entirely to the guest house and let the battery backup control the spark for the propane heat and keep this space at 62 degrees in the winter. This temperature makes it easier to heat up when guests arrive on short notice and keeps the space dry to prevent mold issues but I could set it for lower.

A caution against direct-vent propane heating: Direct-vent propane systems vent all the combustion gasses into the living space and water vapor is a byproduct of propane combustion. Humid spaces soon become moldy spaces. Instead, use a propane heater that vents to the outside and also receives its combustion air from the outside so the inside space can be free of mold-feeding excess humidity. If I’m not mistaken, in some super cold, snow-belt areas, the air is actually quite dry so maybe excess humidity is not a winter issue for you; it is where I live.

In my case, I live full time at my off-grid home so I heat with wood in the winter though I have a propane, whole-house heating system as a backup to the wood stove. I’ve thought about a heat pump for air conditioning in the summer time when I have an excess of electricity from the solar array but since it only gets uncomfortably hot about 3 days out of the year and I have a cool basement I can sleep in for those times, I never installed a heat pump.

Good luck, sounds like a grand project.
Great idea in regard to programming the inverter! We are in a low humidity environment, so the addition of water vapor might be an advantage that I hadn't thought about. Either way, I'm glad you called that out. I'm leaning toward propane, heat pump back-up. We will definitely have a wood stove to use while there, and as a back-up to the back-up.

Thanks Everyone.
 
A caution against direct-vent propane heating: Direct-vent propane systems vent all the combustion gasses into the living space and water vapor is a byproduct of propane combustion. Humid spaces soon become moldy spaces.
Spartan. The Rinnai direct vent furnaces vent directly to the outside. They are expensive.

The inexpensive propane heaters DO NOT VENT. The heaters you’ll find at a hardware store do put all of the moisture back into the space they are heating, causing the moisture issue that you mention.

Would you please edit your post, removing the incorrect reference to “Direct Vent” furnaces?

Here’s a link for you to research:

https://www.rinnai.us/residential/direct-vent-furnaces

These posts live forever, you don’t want to have misinformation last forever as well🙂
 
If winterizing is as easy as making sure the plumbing all flows to a low point to dump water from the lines, maybe I'm making this more complicated than it needs to be
Use an air compressor and blow all the lines out. Heat tape on the primary lines that may be more difficult to blow out. Heat tape is going to be alot cheaper to run vs basicly electric or propane heating 1,800sqft.
 
It kind of depends on how you’ll use your cabin in the winter.

We have a seasonal house on Lake Superior that we keep at 60 degrees so we can use it for short weekends.
 
Spartan. The Rinnai direct vent furnaces vent directly to the outside. They are expensive.

The inexpensive propane heaters DO NOT VENT. The heaters you’ll find at a hardware store do put all of the moisture back into the space they are heating, causing the moisture issue that you mention.

Would you please edit your post, removing the incorrect reference to “Direct Vent” furnaces?

Wheelman55, thanks for catching my mixup with nomenclature. Indeed, I misused the term “direct-vent” when I should have used the term “vent-free.” Vent-free propane heaters vent directly into the space being heated and that is where the potential issue of high humidity levels come from. “Direct-vent” brings outside air into the combustion chamber and directs combustion gasses to the outside. I’ll edit my previous post so it reads correctly.

Cheers,

S
 
In my case, I live full time at my off-grid home so I heat with wood in the winter though I have a propane, whole-house heating system as a backup to the wood stove. I’ve thought about a heat pump for air conditioning in the summer time when I have an excess of electricity from the solar array but since it only gets uncomfortably hot about 3 days out of the year and I have a cool basement I can sleep in for those times, I never installed a heat pump.

Good luck, sounds like a grand project.

Spartan... What system do you have for your "propane, whole-house heating system as a backup?"

Also, based on my quick research, it appears that "direct-vent" propane heaters need to be installed on outside walls.

Does anyone know if there are direct vent's that can be installed on interior walls? These would be vented out to a roof, but that venting might extend 10-12 feet. I'm not seeing anything in my first hasty search.
 
For zone 5b you'll want a diesel heater.

I'm familiar with the "van life" small diesel heaters, but I'm not seeing anything to condition a larger space. Do you have a link for anything you'd recommend?
 
Passive solar succeeds with mass. Consider that.

Clerestory windows will bleed heat because they are high.

Views to the north; maybe figure out window insulation?

If you make a sunroom on the south side, have door(s) to close it off when you will lose heat from the main house; or if it will make the main house too warm.
 

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