System design for off-grid super-insulated home

[Highbeam]

The OP said self building on a tight budget. It’s entirely possible that no financing is necessary, insurance would be easier since there are many off grid cabins.

Yes, with a big propane tank this is no more off grid than the state of Hawaii. You can have a generator, well, septic, furnace, water heater, television, refrigeraton, all the luxuries.

The other end of the off grid spectrum is a tent in the woods.

 

[nynick]

Congratulations on your plan! I built an off the grid cottage in Ontario 25 years ago. It works just fine 3 seasons a year with a modest solar system, battery back up and a Morso wood stove. I would add a few things.

1) Make accommodations for all that south facing glazing. While a nice, bright, warm house is wonderful during the day, you can lose more than you gain during cold nights. If you don't insulate your glazing well, those cold Ontario winters will eat up all that heat.
2) Plan your overhang precisely. You'll thank me in August, especially now that those Ontario summers are getting hotter and hotter.
3) Thermal mass is nice, but unless it's getting direct heat somehow, it takes forever to heat up. Pour the footing for later.
4) Take extra special super duper care when building an airtight structure. I know Canadian builders are more careful with this, but it's your house and you're living in it. Tape all the seams, caulk where you need to, insulate, vapor barrier etc etc. A few hours here or there will reward you with a lifetime of comfort.
5) A well placed wood stove and some floor vents here or there can do wonders for circulation. Keep your ceilings low. Try to figure out if you can pre-heat hot water at the same time with your stove.

Off the grid homes are fun, but they require power of some sort for essential living. You'll need to pump water and heat it too. You'll need to insulate the water pipes from the lake to the house. You need power.

Generators are noisy. You'll be wanting a small photvoltaic system. They're cheap these days.

Get the best stove you can afford. It's along term investment.

Good luck!

nick

 

[begreen]

All good tips nynick!

 

[DickRussell]

This is a very good point! I should clarify, the main reason we want the hydronic system in the slab, is to have an efficient way to keep our pipes from freezing if we were to go away from an extended period of time, not wanting to count on electric baseboards which could drain our batteries in the winter. It won't be used other than that.

A highly insulated and very tight house can go a long time without heat before things get to the point where pipes inside freeze. This is especially true if you have significant glazing that catches the sun during the winter. The house might actually be freeze-proof. Without heat, the inside temperature will drop, but very slowly, initially only a few degrees overnight. As the interior temperature continues to drop, the rate of heat loss and the resulting temperature drop also decrease. Of course, you need to keep plumbing out of exterior walls, and any outside faucets must be the long freeze-proof type with the valve on the inside of the wall (and don't leave hoses attached).

 

[Highbeam]

Already have a huge propane tank. A propane "wood"stove requires no electricity, a direct vent chimney out the wall, and can be set to turn on/off with a thermostat. Modern ones don't even have pilot lights but use a battery and spark ignition. That seems way more logical than electric baseboards running from a battery that may or may not be charged during our long and dark winters.

You can also have a woodstove.

 

[ericdd]

Wow thanks everyone for the feedback. I've been away the last day but I'll try to respond to all the thoughtful comments below:

I don't think any bank will lend for a totally off grid home, but I've been wrong before.

In our area, you can get financing for building off-grid, the trick is most banks don't like self-builds, they want to see a builders warranty (it's a govt program called TARION in Ontario and it's a sham, never pays out for anything). You end up looking at alternative lending markets, some of which are open-minded and some of which are just predatory.

Off the grid homes are fun, but they require power of some sort for essential living. You'll need to pump water and heat it too. You'll need to insulate the water pipes from the lake to the house. You need power.

Generators are noisy. You'll be wanting a small photvoltaic system. They're cheap these days.

Get the best stove you can afford. It's along term investment.

Thanks Nick! I should have been clearer when I said "off-grid", we will have a 4.5kW PV system for well pump, lights, receptacles, etc. The main difference from a modern home is we will have no dryer and no air conditioner ... and resistive loads like range and hot water will be on propane.

A highly insulated and very tight house can go a long time without heat before things get to the point where pipes inside freeze. This is especially true if you have significant glazing that catches the sun during the winter. The house might actually be freeze-proof. Without heat, the inside temperature will drop, but very slowly, initially only a few degrees overnight. As the interior temperature continues to drop, the rate of heat loss and the resulting temperature drop also decrease. Of course, you need to keep plumbing out of exterior walls, and any outside faucets must be the long freeze-proof type with the valve on the inside of the wall (and don't leave hoses attached).

Freeze-proof would be nice, but I don't want to count on it! And good tip about the outside faucet. I haven't hear about freeze-proof types so I'll look into that.

Already have a huge propane tank. A propane "wood"stove requires no electricity, a direct vent chimney out the wall, and can be set to turn on/off with a thermostat. Modern ones don't even have pilot lights but use a battery and spark ignition. That seems way more logical than electric baseboards running from a battery that may or may not be charged during our long and dark winters.

You can also have a woodstove.

The electric baseboards are there for code compliance, as wood heat cannot be primary in my area. Electric baseboards on PV system with no secondary or auxiliary non-electric heat system would be silly indeed.

 

[begreen]

Save the cartons for those token resistance heaters so they can go right back in them after inspection.

4.5kW PV will perform much weaker in the winter due to shorter daylight hours, snow, etc.. And loads will be higher in winter. Will there be a battery bank and a propane generator to carry the load during an extended stormy period?

 

[byQ]

These monastics are trying to do 'smart' building, too. They are in a similar climate zone. I'm going to copy them and build thermal shutters but I'm going have to have mine open side to side instead of up and down.

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[ABMax24]

Thanks Nick! I should have been clearer when I said "off-grid", we will have a 4.5kW PV system for well pump, lights, receptacles, etc. The main difference from a modern home is we will have no dryer and no air conditioner ... and resistive loads like range and hot water will be on propane.

I think you will be disappointed with a 4.5kw system in winter, I think you need to go bigger, of course depending on how you intend to live your lifestyle and how much generator use you consider acceptable during the winter.

Here is a screenshot of my energy use, I have a 3 kw grid-tied roof mounted system, 2 panels west, 4 panels south, 4 panels west. I also use natural gas for all heating; stove, dryer etc, and all appliances are fairly energy efficient and about 3 years old. My system does about 110% of my energy needs, but if I had to go off grid with this system I'd need a generator for about 75% of my electricity needs in winter, and I have no battery losses to account for. I also live in town and therefore don't need to power a well pump or septic pump either. If you have a ground mounted array that you can sweep snow off of will help a lot, but generator use will still be required.

Just some food for thought, although I'm sure some generator use is better than spending a pile more money on oversizing the system for a few months of the year.

 

[ericdd]

4.5kW PV will perform much weaker in the winter due to shorter daylight hours, snow, etc.. And loads will be higher in winter. Will there be a battery bank and a propane generator to carry the load during an extended stormy period?

I think you will be disappointed with a 4.5kw system in winter, I think you need to go bigger, of course depending on how you intend to live your lifestyle and how much generator use you consider acceptable during the winter.

We'll find out! I did a fairly extensive load calculation and sizing work and feel good about it. 4.5kW also goes farther than it used to with LED lighting and high-efficiency appliances, plus we are of course giving up certain comforts. The battery bank is robust (48V, 1100AH) charged by an MPPT charge controller, and there's room for expansion/upgrades on the array if needed. Array is accessible ground mount with clear sky due south, adjustable to 60 degree angle for the winter sunlight. If you have a grid-tied system for payback or net metering they likely set it up to maximize summer sun... off-grid is different, you always size for winter and you don't stand to gain from overproduction in the summer other than being able to add loads.

We'll have a gas generator for emergencies, but my neighbour has an even smaller system, is conscientious with his power usage and didn't have to run it once last winter. Thank you for sharing the energy usage graph though, it's useful having that kind of data for figuring out how to tweak your system.

 

[ericdd]

These monastics are trying to do 'smart' building, too. They are in a similar climate zone. I'm going to copy them and build thermal shutters but I'm going have to have mine open side to side instead of up and down.

Those thermal shutters are genius! I will seriously consider some for my place, even if they're just retrofitted down the line somewhere.

 

[begreen]

Are there any more questions about the wood stove(s)? This thread is interesting, but more green room material so far than hearth related.

 

[byQ]

Is your basement insulated? Is the basement a living space or more like a mechanical space maybe with a washer and dryer? The reason - are you primarily heating the 1600 sq feet or the 2400 sq feet - ie the basement can be colder then the top floors?

 

[ericdd]

Is your basement insulated? Is the basement a living space or more like a mechanical space maybe with a washer and dryer? The reason - are you primarily heating the 1600 sq feet or the 2400 sq feet - ie the basement can be colder then the top floors?

The basement will be unfinished and primarily for utilities, storage, laundry and work space. Separate entrance to keep the mess from wood burning out of the main living space. We might finish a room down there in the future but no immediate plans to do so. I have seen a lot of guides that recommend locating the stove in the main living space, if that's what you're getting at... I get that it's a space heater not central heating - but between the wood mess and the limited living space we have, we're trying to avoid that.

 

[DickRussell]

The basement will be unfinished and primarily for utilities, storage, laundry and work space.....

Although unfinished, I assume that as part of the house being "superinsulated" the basement slab and walls will be insulated. Otherwise heat loss to ground in winter could be a huge parasitic load on the heating system. An unnecessarily cool basement also would detract from using it for working on things the wife really does not want to see done upstairs. Also, uninsulated walls and slab contribute to mustiness in summer, when air dew point regularly is above ground temperature. I hope you plan on having the basement walls sealed against inward migration of ground water, too. Even with that, it might be necessary to dehumidify the basement in summer. Being off-grid makes that a problem, though, considering power requirement for a dehumidifier.

 

[byQ]

A wood stove in an insulated basement is different than a wood stove in an uninsulated basement. You could do something like insulated concrete forms for the basement walls and insulation under the slab for a basement stove - medium size I would guess. Or you could leave the basement uninsulated, put the stove on the 1st floor, and insulate between the basement and 1st floor - small to medium stove. Or, you could put a bigger stove in the uninsulated basement with no insulation between floors - but that kind of works against the 'smart' design of the house.

 

[ericdd]

Although unfinished, I assume that as part of the house being "superinsulated" the basement slab and walls will be insulated. Otherwise heat loss to ground in winter could be a huge parasitic load on the heating system. An unnecessarily cool basement also would detract from using it for working on things the wife really does not want to see done upstairs. Also, uninsulated walls and slab contribute to mustiness in summer, when air dew point regularly is above ground temperature. I hope you plan on having the basement walls sealed against inward migration of ground water, too. Even with that, it might be necessary to dehumidify the basement in summer. Being off-grid makes that a problem, though, considering power requirement for a dehumidifier.

Sorry I realized I didn't actually answer your question! Yes the slab will be insulated R10 and the basement walls R22. No insulation between floors to promote heat circulation.

 

[begreen]

What outside temperature was the 14,000 BTUs/hr at?
I like the combo suggested. The BK stove should provide the steady baseline heat and the PE for boost and visuals. But if the 14K BTUs was @ -20ºC then the second stove probably will not be necessary. Lighting, refrigeration, hw heater and human bodies will contribute to the warmth too.

 

[ericdd]

What outside temperature was the 14,000 BTUs/hr at?
I like the combo suggested. The BK stove should provide the steady baseline heat and the PE for boost and visuals. But if the 14K BTUs was @ -20ºC then the second stove probably will not be necessary. Lighting, refrigeration, hw heater and human bodies will contribute to the warmth too.

The 14K BTU/h was spec'd for -22C temperature... and I'm only buying one stove!

 

[begreen]

The 14K BTU/h was spec'd for -22C temperature... and I'm only buying one stove!

Sorry, I got lost in all the weeds as the thread wandered. That's a good, but low requirement. If that estimate includes heating the basement then I would go for a low and slow BK stove. And definitely a metal chimney. You will not want to be scavenging heat off that flue for the house. It's better to keep the flue a bit warmer to reduce creosote buildup.

 

[SpaceBus]

Sorry, I got lost in all the weeds as the thread wandered. That's a good, but low requirement. If that estimate includes heating the basement then I would go for a low and slow BK stove. And definitely a metal chimney. You will not want to be scavenging heat off that flue for the house. It's better to keep the flue a bit warmer to reduce creosote buildup.

Especially if it's a cat stove burning really low.

 

[semipro]

Are you really off-grid if you're dependant upon propane?
Alternatives may include a heat pump water heater in the basement. It will work well with solar and dehumidify the basement.
For cooking, maybe a wood cookstove, microwave, and induction "hot" plate.

Woodstove heating? Don't underestimate the effects of passive hot air movement. You can take advantage of it with some upfront planning. I'd make sure you have a good way to keep sleeping areas cool and bathrooms warm in the winter. An open floor plan may not be your best friend in some areas.

 

[SpaceBus]

Are you really off-grid if you're dependant upon propane?
Alternatives may include a heat pump water heater in the basement. It will work well with solar and dehumidify the basement.
For cooking, maybe a wood cookstove, microwave, and induction "hot" plate.

Woodstove heating? Don't underestimate the effects of passive hot air movement. You can take advantage of it with some upfront planning. I'd make sure you have a good way to keep sleeping areas cool and bathrooms warm in the winter. An open floor plan may not be your best friend in some areas.

I mentioned the wood cooker, but as usual it proves to be less popular.

 

[Highbeam]

I mentioned the wood cooker, but as usual it proves to be less popular.

The vast majority of Americans/Canadians do not burn wood, the vast majority of wood burners use a regular gas/electric oven to cook food. I’m sure a wood cook stove is charming, I’ve used one, but are they ever actually the best solution?

The OP has propane. A pretty great cooking fuel.

 

[nynick]

It took me along time to figure out why wood was cheap in metro NY and expensive in Ontario. Hardly anyone burns wood around here in NY and the landscapers have to pay to dump the wood from the trees they cut down. You can take it off their hands fairly cheaply. In Ontario cottage country, people burn wood and are willing to pay for it. Simple economics.

If you've never lived in an off the grid home you don't really have a feel for how it goes, or what's important, especially when it's cold out. The simple fact is cooking with wood is inefficient and hot in the summer. It just makes sense to use propane for this and heating hot water. The bigger the propane tank the better. Electricity is at a premium through generation and storage, so you want to use as little as possible. Resistance ANYTHING eats KW's in a hurry. Toaster, coffee maker, even a microwave. You can get away without the last two, but a toaster was our big splurge. LOL.

Getting water and keeping it from freezing is huge. The frost line is a lot lower up there, so your pipes need to be deep and well insulated, but your source needs to be below freezing. If you need a heated water line, well, there's more resistance heating to account for.

If it were me, I'd concentrate on a super tight structure with all my mechanicals inside or in the basement. Make sure your water source is absolutely, positively unimpeachable and will NEVER freeze.. Make sure your wood storage is very close by to where you're going to use it and well covered. Make sure your solar panels are very well secured. Plan for how you might get Hydro to the house at some point in the future. This off grid stuff is great but as you get older so does the inconvenience.

I like the basement idea for the stove. Almost any decent stove will do for your application. Use floor registers to distribute the heat, and small computer fans to push it further if you need to.

Insulation is cheap but well worth the time and effort to do it right.