Redundancy with heating

[TJOPT]

Good day great people …

Let me lay the foundation for my question. I am building a 1560 ft2 home. I am putting up a 12.8 solar array with 28.6 kWh battery bank. This is a starting point with battery storage but for see the potential for needing more. Time will answer this question. I will be tied to the grid as backup when the array fails to provide for my needs.

My question is regarding heat in the winter. I will have 2 mini splits put in that I am sure I will manage on a general day. However, last year the temps in Southern Illinois dipped to such a level the mini split where I am at now did not work. I had to supplement with electric “radiator” style heaters.

I am asking for some wisdom regarding having redundant heat source. I do have access to wood but am trying to avoid the labor involved. I also can do propane. However, I would like to use solar based if possible. Here are some options I have thought of. Sand battery (if you have plans and experience please let me know), re-wire baseboard heaters to dc but my concern is to carry me at night, add additional batteries to carry the “radiator” style heaters.

I am assured there is enough collective wisdom to help guide me … thanks to all in advanced

 

[pvgirl]

Unfortunately in the coldest part of winter your solar(pv or otherwise) is going to be producing at it's minimum, and after a series of cloudy days your solar energy storage will depleted and you will need to use an alternate source for heat. A tool like pvwatts can show how much solar you can expect by month. More solar and more battery storage can help, but you will get to a point where the costs don't provide little payback, that is a solar panel or battery that's capacity is only needed once a year.

Cold climate mini split heat pumps are available that can heat down to -15f which will cover most places. For best efficiency you want to make sure the home you build is well insulated, and air sealed as you can justify, to reduce energy demand year round. Also you want to do a load calculation such manual j or similar(such as the free: https://www.loadcalc.net ), to make sure the equipment you choose is properly sized. Use a site like http://ashrae-meteo.info/v2.0/ to determine what the design temps are for your location. Seems to be 10-15f, with -5f as an extreme low, based on some random southern IL locations.

For completely off grid you would want 3 sources of heat, such as solar, wood, and propane. A propane Direct-Vent Wall Furnace that doesn't require electricity is a common last resort heat source for off grid. Being grid connected means you could use grid as backup for solar, and electric resistance or propane for supplemental heating sources. The best choices are going to be dependent on your goals, and budget.

 

[hwy17]

These kind of direct vent propane heaters don't have any inside to outside air drafting, they intake all their combustion air from the outside and then exhaust it back out. So I think they make a good backup option without creating any draft problems.

Direct Vent Furnaces | Williams

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Otherwise it seems like it would just be space heaters or baseboards running on AC power, why not that?

 

[OM617YOTA]

Wood stove. Bulletproof reliable heat. If I lived anywhere that it got dangerous cold, I wouldn't have a house without a wood stove.

If you only use the wood stove when you need it, wood use, and thus labor, is minimal.

 

[RV10flyer]

Pellet stove or more PV and LFP. I have LP generator- 10kW, wood burner to back up my 52kWpv, 220kWh LFP. All electric home with 16-33 SEER Heat Pumps.

 

[TJOPT]

Unfortunately in the coldest part of winter your solar(pv or otherwise) is going to be producing at it's minimum, and after a series of cloudy days your solar energy storage will depleted and you will need to use an alternate source for heat. A tool like pvwatts can show how much solar you can expect by month. More solar and more battery storage can help, but you will get to a point where the costs don't provide little payback, that is a solar panel or battery that's capacity is only needed once a year.

Cold climate mini split heat pumps are available that can heat down to -15f which will cover most places. For best efficiency you want to make sure the home you build is well insulated, and air sealed as you can justify, to reduce energy demand year round. Also you want to do a load calculation such manual j or similar(such as the free: https://www.loadcalc.net ), to make sure the equipment you choose is properly sized. Use a site like http://ashrae-meteo.info/v2.0/ to determine what the design temps are for your location. Seems to be 10-15f, with -5f as an extreme low, based on some random southern IL locations.

For completely off grid you would want 3 sources of heat, such as solar, wood, and propane. A propane Direct-Vent Wall Furnace that doesn't require electricity is a common last resort heat source for off grid. Being grid connected means you could use grid as backup for solar, and electric resistance or propane for supplemental heating sources. The best choices are going to be dependent on your goals, and budget.

Fantastic information. Thank you very much for response.

 

[TJOPT]

These kind of direct vent propane heaters don't have any inside to outside air drafting, they intake all their combustion air from the outside and then exhaust it back out. So I think they make a good backup option without creating any draft problems.

Direct Vent Furnaces | Williams

Discover our low-profile, highly efficient direct vent furnaces, ideal for maintaining indoor air quality and retaining heat in your home.

www.williamscomfortprod.com

Otherwise it seems like it would just be space heaters or baseboards running on AC power, why not that?

I actually have looked at these. Thank you!

 

[TJOPT]

Wood stove. Bulletproof reliable heat. If I lived anywhere that it got dangerous cold, I wouldn't have a house without a wood stove.

If you only use the wood stove when you need it, wood use, and thus labor, is minimal.

I have 31 acres of wood so wood is not an issue. It is just the labor. I do agree that using it only when needed would save my back! Thank you

 

[TJOPT]

Pellet stove or more PV and LFP. I have LP generator- 10kW, wood burner to back up my 52kWpv, 220kWh LFP. All electric home with 16-33 SEER Heat Pumps.

I would soooooooo like having that much storage but my budget will not allow. I like the LP idea but I am trying to not have to pay for LP as a basis. Thank you tho …

 

[Madcodger]

Advice given so far is great, especially @pvgirl. With grid as backup mini-splits rated down to -14F are likely fine, and you can buy them rated down to -22F now. We have one that’s rated to just 5F and it has worked at lower temps. That said, we always have two forms of heat here in Maine, so I like your thinking. I don’t think you can beat a propane Rinnai direct vent wall furnace for backup heat. One unit handles our open floor plan, reasonably well insulated studio (just under 1200SF) at -17F.

I agree on avoiding wood heat due to the labor. We have about 22 acres of wood we can harvest, but I’m past the point of wanting to cut and split it, and even if someone else does that, I don’t want to store it or feed the stove or worry about it if we’re away. Set the Rinnai to come on at just below the level where you’ll set the mini-splits, and have a generator that can recharge your batteries, and call it a day.

 

[TJOPT]

Advice given so far is great, especially @pvgirl. With grid as backup mini-splits rated down to -14F are likely fine, and you can buy them rated down to -22F now. We have one that’s rated to just 5F and it has worked at lower temps. That said, we always have two forms of heat here in Maine, so I like your thinking. I don’t think you can beat a propane Rinnai direct vent wall furnace for backup heat. One unit handles our open floor plan, reasonably well insulated studio (just under 1200SF) at -17F.

I agree on avoiding wood heat due to the labor. We have about 22 acres of wood we can harvest, but I’m past the point of wanting to cut and split it, and even if someone else does that, I don’t want to store it or feed the stove or worry about it if we’re away. Set the Rinnai to come on at just below the level where you’ll set the mini-splits, and have a generator that can recharge your batteries, and call it a day.

Seems like the collective kinda point to either propane or wood. Not sure I can go wrong with either but redundancy is the key. The minis that am putting in are rated down to -5 (I think) and in the last 25 years of being in my location, there have been only a handful of days that but us below that temp.

Thank you again for the input

 

[Mattb4]

Consider a pellet stove. Their electrical need is small and the pellets are easier to handle than split wood. There is a bit more maintenance of the stove itself over a wood stove. The one disadvantage is how available and at what cost the wood pellets may be in your area.

However if you are building a house I would still have a place for a wood stove and install one. You never know when having something you can fuel by simply going outside and doing some work cutting wood may be a necessity.

 

[RV10flyer]

Seems like the collective kinda point to either propane or wood. Not sure I can go wrong with either but redundancy is the key. The minis that am putting in are rated down to -5 (I think) and in the last 25 years of being in my location, there have been only a handful of days that but us below that temp.

Thank you again for the input

Remember that -5 or -15 just means they will run at that temperature. That doesn’t mean they will put out much heat. If they are sized like most HVAC systems, your balance point is around 25 to 30°F. Anything below that you’ll need some supplemental heat. One can oversize a little bit with these variable speeds/inverter units. That’s what I do.

 

[12VoltInstalls]

The one disadvantage is how available and at what cost the wood pellets may be in your area.

I concur on the pellet stove. I’m not sure if I’d want that as a primary heat source until you start looking at cost per btu.

In my area I just calculated this last week. Pellets are ~60% the cost of #2 heating oil, ~50% the cost of propane, and (believe it or not) a few pennies less than purchased seasoned cordwood. Self-harvested cordwood wins hands down. Coal is inexpensive.

If you bought a couple pallets of pellets and can support the 450-750W of a pellet stove that is an easy choice. An airtight smaller woodstove purchased used and installed in the basement along with ~2 cords of wood would be a good companion to that, and a moderately powerful small backup generator with ~20gal stabilized non-ethanol gasoline on hand and you will have it made, imho.

minisplit>pellets>woodstove sounds very secure to me.

 

[OM617YOTA]

I have 31 acres of wood so wood is not an issue. It is just the labor. I do agree that using it only when needed would save my back! Thank you

If you have folks you can trust and enough wood to support it, tell them they can cut + split a few cords a wood from the property for their own use, if they cut + split an equal amount for you to use yourself.

In addition to the bulletproof backup heat aspect, I also just plain like wood heat. We use the heat pump most of the time for the same reasons you do, but it keeps the house habitable, while the wood stove makes it feel cozy.

We had a six day power outage due to an ice storm a couple years back. I have a medically fragile girlfriend. That wood stove, and a few cords of wood stacked up, meant I had zero concerns about keeping the house warm and her safe.

 

[Supervstech]

Remember that -5 or -15 just means they will run at that temperature. That doesn’t mean they will put out much heat. If they are sized like most HVAC systems, your balance point is around 25 to 30°F. Anything below that you’ll need some supplemental heat. One can oversize a little bit with these variable speeds/inverter units. That’s what I do.

Most minisplit cold weather ratings state they will produce their rated heat output down to that ambient temp.
The Mitsubishi has hyper heat mode to produce their rated heat even lower temp than most.
they will be your best bet to having reliable heating in the winter on PV…
Installing them above he snow line, keeping them clear of buildup, and the best home insulation are very important as well.

 

[RV10flyer]

Most minisplit cold weather ratings state they will produce their rated heat output down to that ambient temp.
The Mitsubishi has hyper heat mode to produce their rated heat even lower temp than most.
they will be your best bet to having reliable heating in the winter on PV…
Installing them above he snow line, keeping them clear of buildup, and the best home insulation are very important as well.

I installed a Fujitsu 9000 btu 33 seer cold WX model. Yeah it really cranks in cold weather. I measured 7A or 1680W last winter. Of course the power shed doesn’t need much heating. Like you, HVAC contractor. I doubt most do it yourself models perform like these two. Of course we paid for them too. And I get a 10 year parts warranty.

Found this info: “Maximum capacity is significantly higher than rated capacity. For heating, maximum capacity is typically 150% to 185% of rated capacity; for cooling, 110% to 150%.

By nameplate capacity and COP, I mean the capacity and COP that the manufacturer reports at the specific test conditions of 60 F indoor/47 F outdoor (for heating) and 80 F indoor/95 F outdoor (for cooling). By rated capacity, I mean the capacity measured at given indoor/outdoor temperatures. Rated capacity is less than maximum capacity. By rated COP, I mean the COP measured at rated capacity at given temperatures. Rated COP is usually the highest COP the heat pump achieves at given temperatures. In other words, rated capacity is an efficiency ‘sweet spot’.”

Their test condition temps make them “appear” better too. I don’t know anybody that keeps the indoor temperature 60 in the winter and 80 in the summer. But I guess there are a few.

For my area, I need about 150% more BTU capacity in heat mode at 10F odb, than I do in cooling mode at 91F odb. So 9000 btu at -5 or -15F odb is not going to do much for 400-450 sqft room. Cooling would be fine. Mini splits are definitely better as far as heat output down to colder temperatures, but they have their limits too. I don’t install many because they are too difficult to do a preventive maintenance on and I don’t carry parts on the truck because there are so many different factory parts needed. I only use them where I have to.

 

[Madcodger]

Remember that -5 or -15 just means they will run at that temperature. That doesn’t mean they will put out much heat.

But they do. We have a Daikin rated to 5F and another rated to -14F. Both have kept buildings we own at 68F at 0F or below. They consume more electricity at low temps because there's less heat to concentrate and move, but they performed well, and still operated more economically then any other heat source except geothermal or wood, if you do the math (I did). And our Mitsubishi in another building is even better!

 

[RV10flyer]

But they do. We have a Daikin rated to 5F and another rated to -14F. Both have kept buildings we own at 68F at 0F or below. They consume more electricity at low temps because there's less heat to concentrate and move, but they performed well, and still operated more economically then any other heat source except geothermal or wood, if you do the math (I did). And our Mitsubishi in another building is even better!

Some do, some don’t. Sounds like you have a good one and sized properly.

 

[OM617YOTA]

The Mitsubishi heat pumps are phenomenal. We had a 25 year old SEER 10 Trane replaced with a variable speed Mitsubishi SEER 18 heat pump, and immediately dropped our power bill by 1/3rd. (Power costs then increased by ~50% and the bill is right back where it was............)
Lowest temp it gets around here is ~15deg or so, but the heat pump had zero issue.

Despite my comments about liking wood heat and having a wood stove, it just doesn't make sense at all to use for day to day heating. Heating with wood and heating with the heat pump cost about the same per month, but heating with the heat pump is pushing a button on the wall, while heating with wood involves hours of labor.

Reminds me, I need to go up on the roof and clean the chimney this weekend, before our nasty weather sets in and it's no longer safe to go up on the roof.