Furnace vs mini splits

[John Galt]

I’m trying to decide between a forced air propane furnace and multiple mini split units in a new construction home. Help me out please.

We have 13kw of solar panels. 24 batteries are 1110 AH at 48V. 240V available from the inverters, 8800W max. We need to run a generator a couple of times a week to charge the batteries Nov-Feb due to mountains blocking the sun for most of the day, but have excess power rest of the year. This is a stand alone system, no grid power. I plan to get a propane fired backup generator to charge the batteries when needed.

The primary heat is from a BK King on the main level. We have a Princess in the basement that is used when it gets deep in the negatives. I load the King twice a day in deep winter and once in the shoulder seasons.

The furnace/splits would be used for emergency backup, if I was injured, old enough to not want to burn, or we went out of town. The generator would kick on when needed to power either system.

I always planned on a propane furnace thinking we didn’t have the electricity to run the splits during the winter. Every room would have heat, and the entire house would be warm but I don't think I would start the furnace for any reason except those listed above, it wouldn’t be worth the cost of the propane.

On the other hand, the splits could take over in the shoulder seasons when I have plenty of power, cool on these hot days, and could be used as zoned heating in the basement without heating the entire house.

The costs would be almost the same:
The furnace would be a high efficiency model with new ducting. I would be running the ducts, the contractor would drop in the unit.
The splits would be three multi zone units with two ceiling cassettes each. I would install these, the contractor might vacuum the lines.

What am I missing?

 

[Whitenuckler]

I’m trying to decide between a forced air propane furnace and multiple mini split units in a new construction home. Help me out please.

We have 13kw of solar panels. 24 batteries are 1110 AH at 48V. 240V available from the inverters, 8800W max. We need to run a generator a couple of times a week to charge the batteries Nov-Feb due to mountains blocking the sun for most of the day, but have excess power rest of the year. This is a stand alone system, no grid power. I plan to get a propane fired backup generator to charge the batteries when needed.

The primary heat is from a BK King on the main level. We have a Princess in the basement that is used when it gets deep in the negatives. I load the King twice a day in deep winter and once in the shoulder seasons.

The furnace/splits would be used for emergency backup, if I was injured, old enough to not want to burn, or we went out of town. The generator would kick on when needed to power either system.

I always planned on a propane furnace thinking we didn’t have the electricity to run the splits during the winter. Every room would have heat, and the entire house would be warm but I don't think I would start the furnace for any reason except those listed above, it wouldn’t be worth the cost of the propane.

On the other hand, the splits could take over in the shoulder seasons when I have plenty of power, cool on these hot days, and could be used as zoned heating in the basement without heating the entire house.

The costs would be almost the same:
The furnace would be a high efficiency model with new ducting. I would be running the ducts, the contractor would drop in the unit.
The splits would be three multi zone units with two ceiling cassettes each. I would install these, the contractor might vacuum the lines.

What am I missing?

If you can I'd say get both, as if you are away and it's really cold, the heat pumps won't work so good. The heat pumps are good for AC though, so I'd get a couple for your bedroom area and hot area's. Then use them for heat when you can too. If you use your basement and don't need AC down there, then maybe just use the furnace there for heat (and wood). Probably expensive to have propane too though.
Edit: Also, if you can get ducts with the furnace that would be great for circulating the air. The furnace will draw very low power too.

 

[bogieb]

I'd think that in the deep of winter your area gets too cold for the minisplit to keep your house warm. I had a mini split put in in 2021 that is good for sown to +5*F. I don't use the mini split in anything below somewhere in the teens though. Part of that is because the defrost cycle goes on so much that it is blowing cold air fairly often so it is basically fighting itself. And part of that is the inside air doesn't "feel" warm even when the thermostat says it is 68 or 70*

And, the minisplit uses a huge amount of electricity for heat. For my 950 sq/ft house, main floor only , I use about 12kwh/day for cooling to a set temp of 74* when the temps are in the high 90's,

and with some heat coming up from the pellet stove in the basement, electric usage is 26+ kwh/day when heating in mid teens (the panels were snow covered for several days, so no production).

However, there are systems that can go to lower temps than the one I got, and they are innovating all the time so YMMV.

 

[Turbo89]

I am planning a new heating system for my house, and it sounds like we’re having the same internal debates. I’m probably a yr or two away from pulling the trigger, but I’ve mostly convinced myself to go with an “Artic Rated” ducted (not ductless!) mini split system with backup resistive heating elements in the duct. I’ll also have a basement wood stove. For hot water I’m still waffling between tankless hot water heater or heat pump based water heater.

The primary benefit of a ducted heat pump system is that you get most of the benefits if ductless, with most of the convenience of forced hot air.

 

[Whitenuckler]

I am planning a new heating system for my house, and it sounds like we’re having the same internal debates. I’m probably a yr or two away from pulling the trigger, but I’ve mostly convinced myself to go with an “Artic Rated” ducted (not ductless!) mini split system with backup resistive heating elements in the duct. I’ll also have a basement wood stove. For hot water I’m still waffling between tankless hot water heater or heat pump based water heater.

The primary benefit of a ducted heat pump system is that you get most of the benefits if ductless, with most of the convenience of forced hot air.

My friend in Victoria retrofitted his electric forced air ducted furnace with a heat pump and loves it. It uses the existing power cable/feed to run it all and has electric elements just in case. He has a gas fireplace in his main room, and there is no basement just some sort of crawl space. I would prefer to have ducts but I must admit I don't miss all the metal ducting in the basement. Plus they get dirty. Also major work and expense to put them in properly.

 

[John Galt]

Thanks all for responding. I’m looking at a cold climate split, or “Arctic rated” as mentioned. They will heat at 100% down to 5F and then will work somewhat down to -13F.

The downside to the splits is I don’t have the electricity when it would be most useful, but that’s when the stove will do all of the work. The upside is maybe I can cut my wood burning season down from October- June to November- February. Another upside, or downside, is I can heat the guest bedroom in the basement when my Mother in Law visits in the summers without roasting the upstairs.

The furnace would be very convenient for those few times I would require it to be running and probably necessary if we stopped burning wood completely. The rest of the time it would be idle.

 

[Turbo89]

Thanks all for responding. I’m looking at a cold climate split, or “Arctic rated” as mentioned. They will heat at 100% down to 5F and then will work somewhat down to -13F.

The downside to the splits is I don’t have the electricity when it would be most useful, but that’s when the stove will do all of the work. The upside is maybe I can cut my wood burning season down from October- June to November- February. Another upside, or downside, is I can heat the guest bedroom in the basement when my Mother in Law visits in the summers without roasting the upstairs.

The furnace would be very convenient for those few times I would require it to be running and probably necessary if we stopped burning wood completely. The rest of the time it would be idle.

Make sure to look up the newer units, I believe Mitsubishi is now rated down to -30F and there’s another down to -38F. My HVAC buddy says they actually generate heat down that cold, but looks efficiency around 20F above there rating.

I believe “hyper heat” is the trade name for the Mitsubishi ones, which is where I am heavily leaning.

 

[EbS-P]

To me the question is how much heat do you need? Do the math using a COP of 1.8 and see if your electric system can keep up. When you are gone can the generator automatically start and charge the batteries?

I vote both. The MR cool mini split systems are cheap and a propane (I’m thinking floor furnace here) could provide emergency heat via thermostat when you are not there.

 

[gthomas785]

If you're considering installing ductwork, I would just get a traditional split heat pump / AC system along with the furnace. This is a common setup down south. The heat pump will do most of the work until it gets really cold then the furnace will take over.

 

[kborndale]

I recently had a comfort aire hyper heat (so it isn't just Mitsubishi) installed which claims to be able to heat down to -22F. Mitsubishi makes quality units, but tack on a sizable extra cost for the name.

 

[Whitenuckler]

I recently had a comfort aire hyper heat (so it isn't just Mitsubishi) installed which claims to be able to heat down to -22F. Mitsubishi makes quality units, but tack on a sizable extra cost for the name.

The problem is they ice up when it gets really cold, I have an Haier Arctic and it has to shut off to defrost. Now that I have my pellet stove plus all the convect heaters, I don't even bother running it on heat below -5C. I would not want those to be my only source of heat when it can go to -10C down to -30C. In fact here about 3 years ago they went to -32C, and people with only heat pumps had to leave their houses.

 

[kborndale]

The problem is they ice up when it gets really cold, I have an Haier Arctic and it has to shut off to defrost. Now that I have my pellet stove plus all the convect heaters, I don't even bother running it on heat below -5C. I would not want those to be my only source of heat when it can go to -10C down to -30C. In fact here about 3 years ago they went to -32C, and people with only heat pumps had to leave their houses.

Agreed, I don't plan on using the split when it gets below +20F. The wood stove does most of the heating and I put an electric fireplace in that bedroom with resistive heating if the stove can't keep up.

 

[Whitenuckler]

Agreed, I don't plan on using the split when it gets below +20F. The wood stove does most of the heating and I put an electric fireplace in that bedroom with resistive heating if the stove can't keep up.

Yes , I have either 1500W or 2000W convect heaters all over my house. One in each bedroom (3), DR (1) Bath (1) so 5 upstairs. I only had one in the basement because they had a minisplit down there. I moved that head to my bedroom, and installed a 2000W right next to the pellet stove. So 2 mini splits, 7 elect heaters and a 43k BTU pellet stove. The only thing that can foul me up is a prolonged power outage when I'm not there. The last big prolonged power outage here was in the fall 3 weeks? was Hurricane Fiona. If that were to happen in January I'd have to come home.

 

[John Galt]

To me the question is how much heat do you need? Do the math using a COP of 1.8 and see if your electric system can keep up. When you are gone can the generator automatically start and charge the batteries?

I vote both. The MR cool mini split systems are cheap and a propane (I’m thinking floor furnace here) could provide emergency heat via thermostat when you are not there.

If the sun is out I can run multiple units, that is the main reason I started looking at these again. For 8 months the batteries are fully charged by 9AM and the rest of the day the power is unused. I need to relearn everything about my solar setup. I memorized how to install it, dropped it in, then forgot most of it. Once I get it moved to the house, I'll make everything permanent and install a generator that will autostart.

Thanks for reminding me about a floor furnace, that was in the running as I was designing the heat system but once the stoves and furnace were picked I moved forward with those. That floor unit might be an additional option in the future if I can't haul wood. I can run the propane while the walls are still open.

 

[Whitenuckler]

If the sun is out I can run multiple units, that is the main reason I started looking at these again. For 8 months the batteries are fully charged by 9AM and the rest of the day the power is unused. I need to relearn everything about my solar setup. I memorized how to install it, dropped it in, then forgot most of it. Once I get it moved to the house, I'll make everything permanent and install a generator that will autostart.

Thanks for reminding me about a floor furnace, that was in the running as I was designing the heat system but once the stoves and furnace were picked I moved forward with those. That floor unit might be an additional option in the future if I can't haul wood. I can run the propane while the walls are still open.

Will your generator run on propane too? I was thinking a propane heater would be good too for something that is automatic, and does not draw much power in the winter when you don't have much solar.

 

[John Galt]

Yes, the new generator will be propane. Currently I have two gas Honda 3300s tied together which I'll use for backup backup, loaning to the neighbors, and running nailguns while away from the house.

I think the stove would be used in deep winter and the splits would transition in during the shoulder seasons and provide some cooling when needed. A floor furnace can be installed in the future for lifestyle changes.

 

[EbS-P]

Yo make an informed decision you need to model your solar production. NREL or maybe it was DOE had a decent calculator. But it doesn’t take snow covered panels into account. You can’t go wrong with solar, heat pumps, and wood stoves.

With above combination and an EV our highest usage is always January. And we’re in hot and humid costal south.

 

[John Galt]

Yo make an informed decision you need to model your solar production. NREL or maybe it was DOE had a decent calculator. But it doesn’t take snow covered panels into account. You can’t go wrong with solar, heat pumps, and wood stoves.

With above combination and an EV our highest usage is always January. And we’re in hot and humid costal south.

It looks like NREL doesn't take mountains into account either. It reported that I get half the energy in January compared to July. Direct sun in Jan is 1.5 hours, July is around 12 hours. Do they still have those globes that calculate from an actual array site?

 

[bogieb]

It looks like NREL doesn't take mountains into account either. It reported that I get half the energy in January compared to July. Direct sun in Jan is 1.5 hours, July is around 12 hours. Do they still have those globes that calculate from an actual array site?

That actually sounds over ambitious as it is the angle of the sun that is important, not how long you have daylight. Although if you are on top of a mountain, it might be better than on the valley floor, morning sun is not very powerful, even in summer.

This is my January production, where production days are either snow or dark skies. Take into account that I have panels on three sides, so cover E, S and W. If they were all on the south side (which I don't have room), the numbers would be a bit better. My worst month is February.

Here is my best day in January

July production

Thank goodness I didn't listen to the calculators on this, as they said I should be getting way more than I do during winter with only a 6.4kw array instead of the 8.0kw array that I have. (I actually LOL'ed when I saw this).

 

[John Galt]

In January, I get more power if it is mostly cloudy vs a clear sky. Reflection off the clouds helps a lot and it extends the production time by a couple of hours. No way that I can produce 10.5 kWh like you, closer to 1.5 in the deep Winter on a good day.

In Summer, it's light enough to see from 4:30AM til 10PM. The sun pops over the mountain at 6:30 and sets over the mountain 12 hours later. I'm get power for longer depending on the clouds.

I understand about the intensity of the rays depending on the angles but I'm not trying to ring out every last Watt 8 months out of the year. The other 4 months I'll go sweep the panels three times a day if needed.

 

[semipro]

Almost certainly not helpful here but interesting -

The Giant Sun Mirrors in Rjukan

The sun mirrors bring sun down to Rjukan Square during winter months, when it is normally shady.

www.visitnorway.com

 

[Whitenuckler]

Almost certainly not helpful here but interesting -

The Giant Sun Mirrors in Rjukan

The sun mirrors bring sun down to Rjukan Square during winter months, when it is normally shady.

www.visitnorway.com

I'm glad I'm was not the one responsible for that calculation of wind sheer force. Maybe they change angle and use a wind sensor to avoid becoming a kite.

 

[John Galt]

I've thought of that, and blowing up the side of the hill. Of course running a power line to the house would be the easiest. 😀