Switch from gas to electric forced air heating after solar?

[Sol Jolla]

Just installed a 4.5 kW system (15 LG300N1K-Gw panels, P300 power optimizers, Solar Edge 3.8 kW inverter) in a small home in coastal San Diego and awaiting for permission to turn on. It's a somewhat small system but more than adequate for our home and lifestyle. We have a ~20 year old forced air gas central heating system nearing the end of its life. We're thinking about replacing it with an electric forced air central heating system so that we can take advantage of unused solar electric capacity. Anybody done anything similar? Thoughts on pro's vs. cons? Thanks-

[DanKegel]

I'm in a similar boat. I sized my solar system large enough to handle adding an A/C and then some, so I am looking at replacing ~10 year old gas furnace and gas water heaters with heat pump-based units. (Resistance heating is right out; that's too inefficient.)

The GE geospring heat pump water heater seems fine, just have to be careful to pick an installer who has done them before, as they seem to be fragile (they can't be transported on their side?!).

I had an energy audit done, and it found huge leaks in the house's envelope and the ductwork. And of course it noticed there is NO INSULATION IN OUR ATTIC.

I'd like to get that all fixed before I replace the furnace, on the theory that it will make it easier to figure out what size heat pump is really needed. But sane people with normal houses would probably have it all done at the same time.

[inetdog]

It is unlikely that you will get more heat per buck from a heat pump compared to piped natural gas. If you are using propane, then a heat pump will do much better in cost. Remember that your grid tie power from your panels is not actually free unless you have badly oversized your system compared to your current usage and are not getting any money back from POCO.

[grywlfbg]

Just installed a 4.5 kW system (15 LG300N1K-Gw panels, P300 power optimizers, Solar Edge 3.8 kW inverter) in a small home in coastal San Diego and awaiting for permission to turn on. It's a somewhat small system but more than adequate for our home and lifestyle. We have a ~20 year old forced air gas central heating system nearing the end of its life. We're thinking about replacing it with an electric forced air central heating system so that we can take advantage of unused solar electric capacity. Anybody done anything similar? Thoughts on pro's vs. cons? Thanks-

With your mild climate an air-air heat pump will work well and cover both your heating and cooling needs (and re-use your existing duct work but I would have it checked for leaks and sealed while you're at it). Geothermal will be overkill. As Dan noted it's a good time to add some insulation, replace door thresholds/seals, etc. If SoCal homes are anything like NorCal homes they're like swiss cheese from an air leakage standpoint :P

[maximizese]

I don't believe electric forced air heating is the right way to go because it is probably the least efficient way of heating. Air as a medium has just about zero resistance and will find it's way out through leaks or whenever an exterior window or door is opened and closed. My house is 60 years old in coastal southern California. I'd added insulation to both the attic and exterior walls, and have tackled leaky doors and windows with improved weatherstripping. When we remodel the house, I'm planning on installing electric (possibly nat gas fueled) radiant floor heating in the bathrooms and bedrooms (they are all adjacent to each other). I've also installed a ceramic wall heater in our sunroom that keeps the room comfy during the winter on only .4kW/hr. I would definitely check out some books from the library and talk to some efficient home designers before open the wallet.

[J.P.M.]

1.) Do not use electric resistance for space heating. The most cost effective thing you can do at this time is get your present heating system checked out. It's probably something like 70% efficient or so when running properly, and will provide heat for about 1/3 or so of the cost of electric resistance heat. If it ain't broke, don't fix it. Get it tuned up and then seal and insulate the ducting.

2.) If you think moving to electric resistance heat will save you money, think again. It won't.

3.) If you are near the coast in San Diego, you have little need of either heating or cooling relative to the rest of the world. Your HVAC bills are quite small.

4.) If you still want to do something after the tuneup, first figure out what you currently spend in a year on heating and cooling total. Then, seal and insulate, with the emphasis on sealing as that's the easiest and least expensive. Figure as a 1st approx. that a new heat pump to replace the current gas furnace and A/C will save you about 20-25% of what you currently pay. Then, price such a heat pump system, and get bready for a long payback period.

While you're at it, add insulation to your existing water heater tank. Probably 6 month payback or less.

[J.P.M.]

I don't believe electric forced air heating is the right way to go because it is probably the least efficient way of heating. Air as a medium has just about zero resistance and will find it's way out through leaks or whenever an exterior window or door is opened and closed. My house is 60 years old in coastal southern California. I'd added insulation to both the attic and exterior walls, and have tackled leaky doors and windows with improved weatherstripping. When we remodel the house, I'm planning on installing electric (possibly nat gas fueled) radiant floor heating in the bathrooms and bedrooms (they are all adjacent to each other). I've also installed a ceramic wall heater in our sunroom that keeps the room comfy during the winter on only .4kW/hr. I would definitely check out some books from the library and talk to some efficient home designers before open the wallet.

Always minimize the load before replacing equipment as you have done, and always educate before loosening the purse strings.

Stick with natural gas if available. Whether radiant heat floor or forced air or boiler circulation, CH4 fired equipment is almost always the most cost effective way to heat a home. Radiant floor heating is nice, but if done with electric resistance, the fuel cost is very high relative to nat. gas. Ceramic heating is electric heating. Stick with nat. gas if at all possible.

[Sunking]

Agree NG is the way to go.

[J.P.M.]

With your mild climate an air-air heat pump will work well and cover both your heating and cooling needs (and re-use your existing duct work but I would have it checked for leaks and sealed while you're at it). Geothermal will be overkill. As Dan noted it's a good time to add some insulation, replace door thresholds/seals, etc. If SoCal homes are anything like NorCal homes they're like swiss cheese from an air leakage standpoint :P

It's almost always more cost effective to not use something than to get more of it. Hence, reduced use followed by conservation measures are almost always more cost effective first and second steps before new equipment, especially PV.

From what I've seen, most homes in So. CA are energy sieves and built in the days of cheap energy. Title 24 helps a lot, but those improvements take time to work their way through the housing stock. If most current homes around here were in a cold climate, the annual HVAC bills would be a lot higher. A 40 deg. F. delta T on heating is about 2X as hard to moderate as 20 deg. F delta T for cooling.

[Logan005]

If you have Solar, Gas heat is ideal. Switching to electric heat would be going backwards. When you have Solar electric, you should cook, heat and hot water with gas.

[Willaby]

We have a ~20 year old forced air gas central heating system nearing the end of its life. -

Curious, who is determining that a ~20 year old system needs to be replaced? We're also in coastal San Diego and our current "Payne" is ~30 years old and works great. I have a 1980 vintage rental in hot Riverside with the original unit that still does the job. Granted the 1980 unit is overdue and likely expensive (probably a SEER 6 or 7) to run, but the tenant hasn't complained. Our home unit is probably a SEER 8 or 9 and does fine, especially since we only use it a few days a year. I barely maintain it, service maybe once every 4-5 years.

[Ian S]

If you have Solar, Gas heat is ideal. Switching to electric heat would be going backwards. When you have Solar electric, you should cook, heat and hot water with gas.

Gas dryer too.

[DanKegel]

If you have Solar, Gas heat is ideal. Switching to electric heat would be going backwards. When you have Solar electric, you should cook, heat and hot water with gas.

Unless your goal happens to be to minimize your carbon footprint, in which case heat pump style heating and good insulation is probably a better choice than gas for some things. (I'll probably never switch away from a gas stove; they're too good, they don't actually burn much gas, and switching to electric would be an anachronism in my 1912 house.)

[Sunking]

Unless your goal happens to be to minimize your carbon footprint, in which case heat pump style heating and good insulation is probably a better choice than gas for some things. (I'll probably never switch away from a gas stove; they're too good, they don't actually burn much gas, and switching to electric would be an anachronism in my 1912 house.)

Wrong, dead wrong. There is no more efficient means of heating with NG compared to a heat pump. Not only less expensive, but more efficient which means less emissions.

[DanKegel]

Wrong, dead wrong. There is no more efficient means of heating with NG compared to a heat pump. Not only less expensive, but more efficient which means less emissions.

Assuming a house in isolation:
If you use natural gas, you're emitting co2.
If you use solar, you're not emitting co2.

Am I missing something?