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

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.
Check out the Rinnai link that I have in post #18. Rinnai has a pretty long max vent length.
 
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.
I’ll get back to you with model numbers of the whole-house and the direct vent unit shortly. I’m out of town at the moment, probably till Wednesday.

S
 
Best solution in the US today is a Wiessman hydronic heat pump and in-floor radiant heat. Insulate below the slab and design for low-temp hot water (<120F). Keeping the slab at 55-60F gives you a great thermal battery for outages. A wood burning stove inside is great for warm-up when you arrive, but you can also control the heat pump remotely to bump up the temperature.

For bonus points, add radiant heat to the shower walls.
 
Best solution in the US today is a Wiessman hydronic heat pump and in-floor radiant heat. Insulate below the slab and design for low-temp hot water (<120F). Keeping the slab at 55-60F gives you a great thermal battery for outages. A wood burning stove inside is great for warm-up when you arrive, but you can also control the heat pump remotely to bump up the temperature.

For bonus points, add radiant heat to the shower walls.
The problem with inslab heating in a seasonal/weekend cabin is these systems can take quite a long time to heat from 40 to 70*. So by the time your packing up after a weekend the slab is up to temp.
 
Best solution in the US today is a Wiessman hydronic heat pump and in-floor radiant heat. Insulate below the slab and design for low-temp hot water (<120F). Keeping the slab at 55-60F gives you a great thermal battery for outages. A wood burning stove inside is great for warm-up when you arrive, but you can also control the heat pump remotely to bump up the temperature.

For bonus points, add radiant heat to the shower walls.

Thanks Shimmy. We are planning on doing at least R10 below slab. I'm now going down the rabbit hole of propane boilers and using in-floor radiant as the "base heat" versus direct vent propane units. I'm researching how much propane both options would be using in the cold season. The downside to in-floor radiant is one failure point versus a few if we do multiple direct vent units. I do prefer the idea of in-floor radiant.

The problem with inslab heating in a seasonal/weekend cabin is these systems can take quite a long time to heat from 40 to 70*. So by the time your packing up after a weekend the slab is up to temp.

We will have connectivity, so it appears there are some systems that would allow for us to bump up the temp prior to arriving.
 
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.
Most of the units I've seen have a 46f freeze-protection mode. Both our Tosot (Gree) and Pioneer units have this mode. For normal heating the minimum setting is 61f.
 
Water is from 300' well
Any chance you have 2 wells to loop, for geothermal? That saves a lot of excavating...
You possibly could run 2 lines in a closed loop down the single well depending on your heat load.....


Air to air Heat pumps are great especially when it gets cooler and wood stove makes the house to hot to fast. Some are rated to -20C
 
Most of the units I've seen have a 46f freeze-protection mode. Both our Tosot (Gree) and Pioneer units have this mode. For normal heating the minimum setting is 61f.
Thank You.

Any chance you have 2 wells to loop, for geothermal? That saves a lot of excavating...
You possibly could run 2 lines in a closed loop down the single well depending on your heat load.....


Air to air Heat pumps are great especially when it gets cooler and wood stove makes the house to hot to fast. Some are rated to -20C
We just have the one well unfortunately. I've got a call scheduled with my neighbor to discuss his system... he's had ground source pump in place for 20 years, so maybe there are some differences between what's available now.

The Air to Water HP seems like another option for radiant only. What I'm reading sounds good, but I always fear "if it sounds too good to be true..."
 
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.
Our propane whole-house system is a high efficiency (95.5%AFUE rating) propane system made by Tempstar but there are other manufacturers of this style of high efficiency furnace out there to choose from. Again, we usually just heat with our wood stove but the whole-house unit is available when desired.

For our 460 square foot guest house, the direct-vent propane heater can be vented through the roof and does not require installation against an exterior wall. This heater is a Hampton H15. The vent pipe seen here is a concentric pipe where the a smaller diameter combustion-air pipe runs through the center of the exhaust pipe.

This heater is one of the smaller ones out there but it’s perfect for heating the small space that it’s in. Though ours is against an exterior wall, it can be installed along an interior wall and vented through the roof (up to 30 vertical feet) instead. Here’s a pic:
IMG_0465.jpeg
 
Our propane whole-house system is a high efficiency (95.5%AFUE rating) propane system made by Tempstar but there are other manufacturers of this style of high efficiency furnace out there to choose from. Again, we usually just heat with our wood stove but the whole-house unit is available when desired.

For our 460 square foot guest house, the direct-vent propane heater can be vented through the roof and does not require installation against an exterior wall. This heater is a Hampton H15. The vent pipe seen here is a concentric pipe where the a smaller diameter combustion-air pipe runs through the center of the exhaust pipe.

This heater is one of the smaller ones out there but it’s perfect for heating the small space that it’s in. Though ours is against an exterior wall, it can be installed along an interior wall and vented through the roof (up to 30 vertical feet) instead. Here’s a pic:
View attachment 262820

Thank you for sharing this info Spartan. I've been doing a bunch of research and a few things standout (that this fine group has called out a few times in this thread already.)


1. I am going to have to implement multiple solutions. I was made aware that a recent storm kept panels covered in snow until they were cleaned off, which I won't have the luxury of doing quickly.
2. Propane is going to have to be one solution - Unless we do a monster battery bank, which just doesn't make sense (see above)
3. Anything we can do now from a design perspective in order to retain as much heat as possible will pay off in spades over the life of this cabin.

Option #1: Second favorite, as it's primarily reliant upon propane, but it's probably a better option in my situation.
  1. Propane condensing boiler for radiant heat. I looked at electric boilers, but the draw is too high.
  2. Mini-splits for back-up heat
  3. Mini-splits will provide A/C (wasn't a priority, but nice benefit for the 2-3 weeks when it might be used)

Option #2: Would be my first choice, but I'm not confident on energy requirements.
  1. Air to Water Heat Pump - for radiant heat only. DHW with HPWH
  2. Propane direct vent heaters
  3. No A/C
  4. FUTURE - we could do "home runs" to each room for future use of wall mounted distribution for any A/C needs

Feel free to blow holes in either of those options!

I've been using ChatGPT as well. I believe the dataset is current through late 2021, so some of this might be outdated, but it "feels" accurate to me. I was researching electric boiler needs and air to water heat pump electrical needs. I realize I don't know the true heating load of this property yet. The heat pump wins out big time in this assessment, which is not surprising.


You said:​

What would be my electrical needs for the electric boiler in a typical heating season at my cabin?

ChatGPT said:​


To estimate the electrical needs of an electric boiler for your cabin during a typical heating season, we'll consider several factors:


Key Inputs for the Calculation

  1. Cabin Size & Heating Load:
    • Total area: 1,800 sq. ft.
    • Open kitchen/living area: ~1,100 sq. ft.
    • Climate Zone: 5b (cold winters with moderate heating requirements).
  2. Estimated Heat Demand (BTUs):
    • A Pretty Good House standard typically requires 10-20 BTUs/sq. ft. per hour for heating.
    • For 1,800 sq. ft., the heat demand is:1,800 sq. ft.×15 BTUs/sq. ft.=27,000 BTUs/hour.1,800 \, \text{sq. ft.} \times 15 \, \text{BTUs/sq. ft.} = 27,000 \, \text{BTUs/hour}.1,800sq. ft.×15BTUs/sq. ft.=27,000BTUs/hour.
  3. Electric Boiler Efficiency:
    • Near 100% (1 kW = 3,412 BTUs).
  4. Heating Season Duration:
    • ~6 months (October to March) in central Utah.
    • Assume 10 hours/day of heating on average.
  5. Electrical Energy Use:
    • Total heating hours: 6 months×30 days/month×10 hours/day=1,800 hours.6 \, \text{months} \times 30 \, \text{days/month} \times 10 \, \text{hours/day} = 1,800 \, \text{hours.}6months×30days/month×10hours/day=1,800hours.

Step 1: Convert Heating Load to kW

  • 27,000 BTUs/hour ÷ 3,412 BTUs/kW = 7.91 kW/hour.

Step 2: Estimate Total Energy Use (kWh)

  • 7.91 kW/hour×1,800 hours=14,238 kWh/season.7.91 \, \text{kW/hour} \times 1,800 \, \text{hours} = 14,238 \, \text{kWh/season.}7.91kW/hour×1,800hours=14,238kWh/season.

Step 3: Daily and Monthly Use

  • Daily Use: 7.91 kW/hour×10 hours=79.1 kWh/day.7.91 \, \text{kW/hour} \times 10 \, \text{hours} = 79.1 \, \text{kWh/day.}7.91kW/hour×10hours=79.1kWh/day.
  • Monthly Use: 79.1 kWh/day×30 days=2,373 kWh/month.79.1 \, \text{kWh/day} \times 30 \, \text{days} = 2,373 \, \text{kWh/month.}79.1kWh/day×30days=2,373kWh/month.

Key Considerations

  1. Solar System Sizing:
    • Ensure your solar panels and battery bank can handle the daily/seasonal demand.
    • Winter has less solar production, so you may need backup or additional storage capacity.
  2. Thermal Storage:
    • Adding a water-based thermal storage tank could help run the boiler intermittently, reducing peak electrical loads.
  3. Supplemental Heating:
    • Consider using passive solar heating, a wood stove, or high-efficiency heat pumps to reduce boiler dependency.
  4. Energy Efficiency:
    • Additional insulation, airtightness, and high-performance windows can further reduce heating loads.

How many watt hours per day would I need?

ChatGPT said:​


To estimate how many watt-hours per day you’d need to power an air-to-water heat pump for radiant heating in your cabin, we can calculate based on the following:


Assumptions

  1. Heating Load:
    • Your cabin's heating demand is 20,000 BTUs/hour on average.
  2. Heat Pump Efficiency:
    • A cold-climate heat pump has a COP of 3.0, meaning it uses 1 kWh of electricity to generate 3 kWh (10,236 BTUs) of heat.
  3. Daily Operating Hours:
    • Assuming the heat pump runs 10 hours/day to meet heating needs.
  4. Electricity Conversion:
    • 1 kWh = 3,412 BTUs.

Step-by-Step Calculation

1. Energy Needed per Day (BTUs)

Heating load × daily runtime:

20,000 BTUs/hour×10 hours/day=200,000 BTUs/day20,000 \, \text{BTUs/hour} \times 10 \, \text{hours/day} = 200,000 \, \text{BTUs/day}20,000BTUs/hour×10hours/day=200,000BTUs/day

2. Electricity Needed (kWh)

Divide total BTUs by the heat pump efficiency and conversion rate:

200,000 BTUs3.0 COP×3,412 BTUs/kWh≈19.6 kWh/day\frac{200,000 \, \text{BTUs}}{3.0 \, \text{COP} \times 3,412 \, \text{BTUs/kWh}} \approx 19.6 \, \text{kWh/day}3.0COP×3,412BTUs/kWh200,000BTUs≈19.6kWh/day

3. Watt-Hours per Day

19.6 kWh/day×1,000=19,600 Wh/day19.6 \, \text{kWh/day} \times 1,000 = 19,600 \, \text{Wh/day}19.6kWh/day×1,000=19,600Wh/day

Result

You would need ~19,600 watt-hours (Wh) per day to power an air-to-water heat pump for your radiant heating system.
 
Just for reference I have a 1700 sq ft house with a basement.
Basically all styrofoam, built with SIPs Panels.
It is quite tight air wise,
I have 1 air to air heat pump 12000 btu in the middle of the house living room.
It was a $1500.00 Amazon special.
Its heats and cools extremely well to -5c The bedrooms that are farther away, get cool when its -5 but for the price these units, I would put one in a new build regardless of what else you are doing for heat...
It works excellent for keeping the humidity down in a air tight house...

Their 24000 btu unit is a nice big unit
Helped someone else install one.
 

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Just for reference I have a 1700 sq ft house with a basement.
Basically all styrofoam, built with SIPs Panels.
It is quite tight air wise,
I have 1 air to air heat pump 12000 btu in the middle of the house living room.
It was a $1500.00 Amazon special.
Its heats and cools extremely well to -5c The bedrooms that are farther away, get cool when its -5 but for the price these units, I would put one in a new build regardless of what else you are doing for heat...
It works excellent for keeping the humidity down in a air tight house...

Their 24000 btu unit is a nice big unit
Helped someone else install one.
Wow... that is a fantastic data point and thanks for sharing. I'll be doing a deeper dive with my architect on our next meeting to determine how to maximize the tightness of the envelope.

Do you use an HRV or ERV to bring in fresh air?
 
no air handler of any kind.... but I have a wood stove, which pulls out the humidity.... and the heat pump can humidify if you set it. If a lot of cooking gets done sometimes it can go up... but I am aware and a window open or fan over the stove, will solve that... I do have a few leaky door seals.

In a new build I would plan for it, but who ever does the HVAC requirement design will have a fit and make you put a super big unit in....

This 12000btu works fine, but if did it again I probably would do the 24000btu
it is a tougher unit and feels less plasticity.... or get an LG unit.

fyi when I first built it. It was quite abit worse.... all the wood and drywall is releasing its moisture, now it's way better.
 
Just for reference I have a 1700 sq ft house with a basement.
Basically all styrofoam, built with SIPs Panels.
It is quite tight air wise,
I have 1 air to air heat pump 12000 btu in the middle of the house living room.
It was a $1500.00 Amazon special.
Its heats and cools extremely well to -5c The bedrooms that are farther away, get cool when its -5 but for the price these units, I would put one in a new build regardless of what else you are doing for heat...
It works excellent for keeping the humidity down in a air tight house...

Their 24000 btu unit is a nice big unit
Helped someone else install one.
Is this a DC/solar mini split?
 
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?
There is an ace hardware out in BFE nevada that uses a diesel heater. Not sure what brand it is but vevor has a 215,000 BTU diesel heater. That will take the chill off zone b.
 
Best piece of advice I can give after 30 years designing and installing radiant floor heating is do a correct heat loss and tubing design, it is the most important piece of the radiant system. You don’t want to have to do this:

DFD71CE6-68EB-4604-81FF-FCA849AAD36D.jpeg
 
Best piece of advice I can give after 30 years designing and installing radiant floor heating is do a correct heat loss and tubing design, it is the most important piece of the radiant system. You don’t want to have to do this:

View attachment 264109
Dang! That looks like a disaster. Where’d they go wrong? Could you share more details? It looks like there’re some “lessons learned” to be had from that photo so if you can elaborate, I’m sure the readers would appreciate it.
 
I have a Mr. Cool mini-split and it's been 15F and still had heat without issue. My central air heat pumps in other houses always went to emergency heat when they hit 40F. They were electric back-up heat and you just gave the power company an IV to your bank account.
 
Best piece of advice I can give after 30 years designing and installing radiant floor heating is do a correct heat loss and tubing design, it is the most important piece of the radiant system. You don’t want to have to do this:

View attachment 264109
Dang! Agreed with Spartan... any insight as to what went wrong would be great to know. Thank You.
 
There is an ace hardware out in BFE nevada that uses a diesel heater. Not sure what brand it is but vevor has a 215,000 BTU diesel heater. That will take the chill off zone b.

Diesel heaters for a home are called oil burners. They are a diesel burner inside a forced air furnace, similar to a natural gas whole home furnace. If the tank is inside, you burn #2 diesel (heating oil), if the tank is outside, you burn #1 diesel (kerosene). Kerosene costs more, but can handle colder temps without gelling. Heating oil has more energy per pound/gallon/$ than kerosene. If you don’t have a delivery service nearby, you can use on road diesel in an oil burner, but you’re paying road tax at somewhere around $0.60 per gallon. Off road diesel would be pretty close to same price as heating oil.
 
Best piece of advice I can give after 30 years designing and installing radiant floor heating is do a correct heat loss and tubing design, it is the most important piece of the radiant system. You don’t want to have to do this:

View attachment 264109
Looks like an outside pad?????
Not sure how its screwed up.
Rule of thumb 1 ft of pipe per sq ft. Then add an extra loop or two on the outside perimeter.

Rule number 2 do not let the loop freeze.
If it can freeze, use antifreeze
 
Dang! That looks like a disaster. Where’d they go wrong? Could you share more details? It looks like there’re some “lessons learned” to be had from that photo so if you can elaborate, I’m sure the readers would appreciate it.

Wrong size and length of tubing(to high a head loss)?would not heat correctly. When installing radiant you basically have a bunch of individual heat losses in the structure, rooms can have different on center and flow requirements depending on if they are interior or a wall of glass.

1F11E1D5-D218-4E9E-A421-1C3EBAC66F33.jpeg
 
We have a camp in north western Maine with similar challenges. 20 miles in on logging roads. For most of winter access with snow machines only. There is no cell access, satellite/Starlink only. We considered setting up a propane system to mainain a minimum temp all winter, and solar to keep the wifi on to be able to monitor everything. The structure is full basement timberframe/SIP and super tight. Northern exposure so not great passive solar. Quadrafire wood stove for heat.

We have decided to winterize the camp and when we visit we use the outhouse, fire up the wood stove and 'rough it'. Carry in food and water. Too many challenges to try and get a propane/solar system in place to run remotely without monitoring. If something goes wrong and monitoring or power was lost we'd have visit the site urgently to address. Batteries are brought home and stored at RT over the winter to avoid freezing. Looking forward to future battery tech that does not mind freezing.

If its withing your means, tapping into the grid is the simplest option? Or the hire a property manager.
 
If its withing your means, tapping into the grid is the simplest option? Or the hire a property manager.
Thanks for the intel. 20 miles down logging roads sounds fantastically remote.

Tapping into the grid is going to cost more than building an off-grid system, so that's the direction we are going. That being said, I'm leaning toward making it easy to winterize... we've been "roughing it" in a pop-up at the site for the last 6 years, but once November hits, it's too damn cold for canvas walls.

I'm digging into my Option #2 above in more detail and I am leaning on some electric consultants for help. They are echoing the same thing here... build it tight up front and I should be able to make it work on electricity (with propane backup.)

Option #2:
  1. Air to Water Heat Pump - for radiant heat only. DHW with HPWH
  2. Propane direct vent heaters Propane generator to run ATWHP
  3. No A/C
  4. FUTURE - we could do "home runs" to each room for future use of wall mounted distribution for any A/C needs
 

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