Switch from gas to electric forced air heating after solar?

[Mike90250]

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

Generally, I'd not do it. New Gas FAU are much more efficient than older ones, and they still use electric for the fan, which runs longer with the HE units.
At least wait 2 years if you can, to see what the electric usage/generation actually ends up being, don't want to dig yourself into a hole.

[firesense]

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-

Yeah, electric heater are quite a good to have that gas heaters. I personally have in my house and they work quite well. It is just that you have to choose that according to your needs otherwise it can be bit tough.

[ncs55]

Sol Jolla, As I previously mentioned, I am not here fishing for business. I would love to see your home and I work with one of the most knowledgeable restoration contractors in the San Diego areas. Your project is not the standard type of project from what I have read. I respect what you are trying to achieve and would be all over it if I were to have met you outside of this forum. Thank you for asking and If you can find me, I am all in, but this forum is not a vehicle for me to advertise on. I came here to help out people like yourself and the self installers, that they can benefit from some of my experiences in the field.

[Sol Jolla]

Thanks all. Lots to ponder. Nice summary. Sorry, I don't check this board that often, since we travel a lot--another reason why we'll have excess capacity, at least for a few years.

The house actually had a major rebuild 15 years ago. The foundation, electrical and plumbing was brought up to contemporary code. Doors and windows are a different issue since a goal of the remodel was to restore it to original form.

I can't figure out the PM (is it because I'm new?). Any rate, ncs55 please PM me with the website for your business. Thanks-

[J.P.M.]

To recap: the OP says:

-- paraphrase --
Small home, 110 years old, in coastal San Diego, bought a few months ago
Difficult to seal up windows and doors without compromising historic integrity/charm
Attic (where the furnace is located) could be better insulated
Just turning on 4.5 kW solar system, somewhat small but more than adequate for our home and lifestyle
Has central AC
Has ~20 year old forced air gas central heating system. Pre-sale inspection said couldn't expect much more life from the furnace based on it being 20 years-old.
Thinking about replacing furnace with an electric forced air central heating system so that we can take advantage of unused solar electric capacity.
Goal with switching to electric would be to cut costs by maximizing solar use, since the system should make in excess of what we are currently drawing from the grid and in the ideal case would eliminate natural gas consumption and still have net zero or negative consumption from the grid.
-- end paraphrase --

Step 1, as lots of folks have noted, is increasing efficiency.
Have you addressed all the low hanging efficiency fruit like getting rid of incandescent bulbs and old fridges?
And have you had an energy audit? If nothing else, SDGE will come out and do a quickie audit for free, see http://www.sdge.com/save-money/solut...save-you-money

Step 2 might be to estimate your heating and cooling needs. How much gas does it take to heat your house now? How much electricity does it take to cool your house now? Does the SDGE bill show usage for the previous owner?

Step 3 is look for a heating system that meets your needs and fits your energy and cash budget. If you can't find one, go back to step 1.

Everyone here is rooting for you. There are lots of opinions about what's practical and about whether going net zero is a good idea, but we're all here to help answer your questions. Good luck!

Dan: For once, I agree with you - as in stay on topic. Sorry for my drifting.

[DanKegel]

To recap: the OP says:

-- paraphrase --
Small home, 110 years old, in coastal San Diego, bought a few months ago
Difficult to seal up windows and doors without compromising historic integrity/charm
Attic (where the furnace is located) could be better insulated
Just turning on 4.5 kW solar system, somewhat small but more than adequate for our home and lifestyle
Has central AC
Has ~20 year old forced air gas central heating system. Pre-sale inspection said couldn't expect much more life from the furnace based on it being 20 years-old.
Thinking about replacing furnace with an electric forced air central heating system so that we can take advantage of unused solar electric capacity.
Goal with switching to electric would be to cut costs by maximizing solar use, since the system should make in excess of what we are currently drawing from the grid and in the ideal case would eliminate natural gas consumption and still have net zero or negative consumption from the grid.
-- end paraphrase --

Step 1, as lots of folks have noted, is increasing efficiency.
Have you addressed all the low hanging efficiency fruit like getting rid of incandescent bulbs and old fridges?
And have you had an energy audit? If nothing else, SDGE will come out and do a quickie audit for free, see http://www.sdge.com/save-money/solut...save-you-money

Step 2 might be to estimate your heating and cooling needs. How much gas does it take to heat your house now? How much electricity does it take to cool your house now? Does the SDGE bill show usage for the previous owner?

Step 3 is look for a heating system that meets your needs and fits your energy and cash budget. If you can't find one, go back to step 1.

Everyone here is rooting for you. There are lots of opinions about what's practical and about whether going net zero is a good idea, but we're all here to help answer your questions. Good luck!

[J.P.M.]

We have many systems here in San Diego county that are just what I described and are saving the owners lots of money. And actually our thermal systems require less maintenance than a PV system. There are pump or sensor failures here and there but that's about it. We design our systems to last. Contrary to what you believe and or are saying. I am not here fishing for business. More to educate people like yourself on what I have learned and seen in the last 15 years in this industry. Whatever I can do to help stop the crummy installations that are failing everyday, costing the consumer in the long run.
Respectfully, You are incorrect about the need for heating in SD county, and if used properly thermal management is a very important option, especially where a small amount of heat is needed. So Cal is filled with many different micro climates and a lot of them experience colder than average temps. While some experience hotter than average temps. The thermal assist is a perfect solution for the colder climates. In most cases it is all the homeowner needs for heating their home and the payback is faster than just a standard SHW system. Works great on the coast too. You or I might not think an area is cold but we are not the person living at that location. Do the math, thermal is way more efficient than PV.
It is sad that you suspect what I sell is not cost effective. You obviously have never retrofitted an existing inefficient home into an energy saving home. Or improved the quality of someone's life with this process. It takes a combination of systems and or equipment upgrades to achieve this goal. Do you know about thermal assisted AC units? The hotter it gets the less energy it takes to cool your home. There are also the NG fired AC units that also save over the standard electric units. How about Ice Bank cooling for commercial entities? Radiant barrier and many other options must also be considered in the right combination for the particular application and what the customer wants to achieve.

On my opinion that you're prospecting for business: Let's just say I have a skeptical and cynical nature.

As for (residential) retrofitting and any experience I may have with it, I'd refer you to another current thread running that has one of my posts for a reference to some prior experience.

As for other things you mention with respect to energy design/management : I've seen, or designed, or done failure analysis on what I think is a fair amount of heat transfer equipment since changing careers in the mid '70's, getting reeducated and then working as a P.E. (mechanical) with responsible charge, or as part of a team doing the thermal and/or mechanical design of boilers, heat exchangers, power generating systems, and other pressure vessel and energy producing and handling equipment and systems, including some for nuclear and conventional power plants and systems for the U.S. Navy, as well as for chemical plants and refineries.

FWIW, I changed careers because I got interested in solar energy as a way to stay warm in Buffalo and not go broke doing it. Solar, and solar thermal in particular, has been more than a hobby but less than a fulltime job. I'd like to think I know a bit about it, including efficiency. I can always learn stuff and look forward to your contributions to this venue.

It seems we may agree that there are a lot of poorly designed and constructed solar installations.

[J.P.M.]

None what so ever. In TX I lived in that house for 10 years, Here in Panama just over two years. Trust me if water and moisture were a problem would show up here in Panama. All that is avoided by spraying a sealer on the concrete and using 2 x 2 furring strips for exterior and interior wall finish.

Only thing negative things I can say about it is modifications like moving a wall, cutting a hole for a window or door ect.... Additionally ventilation is required because the house is so tightly sealed up. Easy fix by exhausting 10% of air, and drawing fresh air in via HVAC system.

It is interesting to watch facial expressions when someone enters for the first time. As soon as you walk in the silence is deafening. All my drywall is sound absorbing with isolators on the furring strips. Even interior walls have thermal/sound insulation.

Understood. Thank you.

[ncs55]

ncs55:

The OP is in a climate that, with a bit but not too much work, doesn't have much need for HVAC.Thermal management is even less important there than elsewhere in San Diego, and that's not much of a need to begin with. Solar thermal is a water heating option, but coupled with heat pump water heater, PV is likely as cost effective and probably less maint. than solar thermal. As for HX retrofits, etc., such things are probably better suited for older climates.

And you're probably right, most people would not consider what you've suggested. While I can agree with some of what you write, particularly about not simply throwing solar at a roof and expecting life to be rosy. In San Diego anyway, I suspect a lot of what you sell is not as cost effective or practical around here as folks would need to consider, even if they knew what to do or what you were writing about. FWIW, sounds to me like you're fishing for business.

We have many systems here in San Diego county that are just what I described and are saving the owners lots of money. And actually our thermal systems require less maintenance than a PV system. There are pump or sensor failures here and there but that's about it. We design our systems to last. Contrary to what you believe and or are saying. I am not here fishing for business. More to educate people like yourself on what I have learned and seen in the last 15 years in this industry. Whatever I can do to help stop the crummy installations that are failing everyday, costing the consumer in the long run.
Respectfully, You are incorrect about the need for heating in SD county, and if used properly thermal management is a very important option, especially where a small amount of heat is needed. So Cal is filled with many different micro climates and a lot of them experience colder than average temps. While some experience hotter than average temps. The thermal assist is a perfect solution for the colder climates. In most cases it is all the homeowner needs for heating their home and the payback is faster than just a standard SHW system. Works great on the coast too. You or I might not think an area is cold but we are not the person living at that location. Do the math, thermal is way more efficient than PV.
It is sad that you suspect what I sell is not cost effective. You obviously have never retrofitted an existing inefficient home into an energy saving home. Or improved the quality of someone's life with this process. It takes a combination of systems and or equipment upgrades to achieve this goal. Do you know about thermal assisted AC units? The hotter it gets the less energy it takes to cool your home. There are also the NG fired AC units that also save over the standard electric units. How about Ice Bank cooling for commercial entities? Radiant barrier and many other options must also be considered in the right combination for the particular application and what the customer wants to achieve.

[silversaver]

OP mention about a small house on coast of San Diego, then a mini splits units will be a good pick for cooling/heating requirement. I had one installed last year, love it. Way better than kick in the 60,000 BTU unit + noise during night time. Most of central units weren't efficiency especially in older houses.

[Sunking]

Any problems so far ? Structural/smells/radon, mold, etc ? Just curious.

None what so ever. In TX I lived in that house for 10 years, Here in Panama just over two years. Trust me if water and moisture were a problem would show up here in Panama. All that is avoided by spraying a sealer on the concrete and using 2 x 2 furring strips for exterior and interior wall finish.

Only thing negative things I can say about it is modifications like moving a wall, cutting a hole for a window or door ect.... Additionally ventilation is required because the house is so tightly sealed up. Easy fix by exhausting 10% of air, and drawing fresh air in via HVAC system.

It is interesting to watch facial expressions when someone enters for the first time. As soon as you walk in the silence is deafening. All my drywall is sound absorbing with isolators on the furring strips. Even interior walls have thermal/sound insulation.

[J.P.M.]

Thanks, I speak from experience. I do like Victorian and Adobe style homes. With today's construction techniques, you can build any architectural finish type your heart desires. As for me, my last two homes I built use 10-inch ICF. The one in TX is finished Faux Adobe exterior, and here in Panama finished in Brown Stone made from concrete. Looks like it was built with local rocks. Once you go ICF, there is no going back. You can heat them with a candle, cool them with a glass of ice tea, and a war could breakout in your yard and you would never hear it. Pretty much fire proof, wind prof, water proof, and bullet resistant.

I had planned on ICF's for the vertical envelope sections of my Borrego Springs desert magnum opus with added/distributed thermal mass and controlled passive solar, but the project stalled and was eventually abandoned for a lot of reasons having naught to do with building techniques or finances. It would have had HVAC as required by code, etc, but in all likelihood would not have been needed much, if at all. Between the building thermal mass and the low heat loss/infiltration rate, the building thermal time constant would have been ~ 300 hours. +/- some.

Any problems so far ? Structural/smells/radon, mold, etc ? Just curious.

[Sunking]

+1, and pretty much as you describe - for me anyway. But it can be and was a real learning experience, including the part where I found out someone had more patience than Job - my 1st wife.

Thanks, I speak from experience. I do like Victorian and Adobe style homes. With today's construction techniques, you can build any architectural finish type your heart desires. As for me, my last two homes I built use 10-inch ICF. The one in TX is finished Faux Adobe exterior, and here in Panama finished in Brown Stone made from concrete. Looks like it was built with local rocks. Once you go ICF, there is no going back. You can heat them with a candle, cool them with a glass of ice tea, and a war could breakout in your yard and you would never hear it. Pretty much fire proof, wind prof, water proof, and bullet resistant.

[DanKegel]

How do you know that ? Did you ask the OP ?

Thanks for calling me on that - I think I hallucinated it.

I'll just go sit quietly in the corner for a while

[J.P.M.]

Well that is the problem with old houses. Even though they could be well built, but there was hardly any consideration on energy efficiency. None would pass any building or electrical codes today. You pretty much have to Gut Them leaving the exterior walls and exterior finish. Once gutted you are likely to find structural issues like rotten wood, water damage, and insect damage that will need repaired. by the time you finish will cost you a lot more than building new. None of the electrical, structural, mechanical, and plumbing will be up to current codes. Just one big PIA.

+1, and pretty much as you describe - for me anyway. But it can be and was a real learning experience, including the part where I found out someone had more patience than Job - my 1st wife.