At PG&E electric rates I doubt that you would want even one electric tankless, much less two of them. I think your idea to upgrade the gas now and revisit electric after your solar installation is probably your best idea.

PG&E gas and electric rates move somewhat independently, which makes it tricky to compare. We went to an electric heat pump tank about 15 months ago in the East Bay for a 2/2 (from a 25-year-old gas tank) and our overall bill has remained comparable for a four-person household, but that's probably in part because the old gas tank was hugely inefficient. We have a 66-gallon tank, I think, up from a 40-gallon gas tank; it seems sufficient for four showers back-to-back but on the rare occasions we do that, seems done by the end. I don't love it because it is crazy loud, though. No way would I put one in the living space. (Ours is in an unfinished basement and we still hear it in the house above.) One unexpected plus, though, is that it cools the air in the room it's in so that it feels like air conditioning--so there is that! We didn't really consider electric tankless for some reason, but that's what I'd be inclined to look at in retrospect. (And yes, multiple units, sized to the uses and located near where they will be used.)

I do think it will be increasingly hard to put gas back in the future, so that could also be a consideration.

Electric tankless for whole house is always a bad idea. In areas where they also do peak metering - such as California -it's a really bad idea. It will cost you an arm and a leg because it will cause very high peak usage.

It requires a massive amount of electricity at one time to heat water in a tankless heater. Even then you don't get many GPM. You would need to redo your entire electric service to supply one heater - let alone two.

Electric tankless (any electric resistance heat, but esp electric tankless ) doesn't play well with solar PV. What does work well is a hybrid electric tank heater.

If you have a basement, buy a large hybrid electric and then run a circulation pump on the plumbing to the upstairs. That will keep the wait reasonable for hot water.

Gas is a good option. It was really stupid for California to outlaw gas. There needs to be big investments in grid capacity, renewables, and probably nuclear. We aren't able to meet the current load on the grid, and we are adding electric vehicles. What's more, there is no current path to a non-carbon future presently besides nuclear. Solar and wind are great, but we have no way to store that energy at scale. Peak electrical use is in the early evening and charging cars at night will only make the mismatch between solar and the demand for energy worse.

Shutting down transition energy sources, such as gas, is not the right answer.

@artemis78

What brand of hybrid electric heater - and how old is it?

The new ones do make some noise, but it should be about the same as a refrigerator.

I would also avoid putting one in a living space, but should be fine in a basement.

Hybrid electric are the least expensive to run of all types - according to the DOE sticker. They cost less than gas tankless, for example.

@Jake The Wonderdog It's a State hybrid electric--I'd have to go look to find the specific model. It's a year old. It is much louder than our refrigerator--seems comparable to an a/c unit (though we don't have one so maybe that's just my perception?) I'm not sure the DOE sticker is indicative of price in California, unfortunately--our electric rates have gone continuously up (at least in PG&E territory) as a result of recent fire liability that has been absorbed by rate payers. Still, our bill is not hugely different than with the gas, and we aren't using substantially more electricity than before we got it so I believe that it is quite efficient. Just no cost "savings" to speak of.

Forget about the tankless. As everyone pointed out, you can't use an electric one, they don't crank out enough hot water for your needs and consume a ton of electricity (do you have extra 4x40 amp circuits available in your service panel? that's just for one unit) and you don't have a reliable energy grid. Gas is no good for you because its an evil fossil fuel. Btw, how are you heating your hot water now? Might have to go with wood burning, although that's probably banned in SF too.

"HU-723692230: As everyone pointed out, you can't use an electric one, they don't crank out enough hot water for your needs and consume a ton of electricity ..."

That's not true as a blanket statement, although there certainly are factors to consider for individual circumstances. I've had an electric tankless for nearly 18 years and never have had an instance of insufficient hot water. Coincidentally I checked the operational info on the unit several days ago when taking a shower. It was running at 22% of capacity so plenty reserve for more concurrent hot water usage.

Agree with dadoes. We had a electric tankless in our condo and it was more than sufficient for us and guests showering.

Condo? That's a Mini house situation and guests are by definition short timers. Nah man, in a full house you can't run 2 showers plus a dishwasher or washer with an electric tankless without running into hot water problems. Sure you can schedule everyone's showers and your housekeeping, but that's not a way to live if you have kids or teens. You'll get best performance if you live in a suburban area with public water for sure, but if you are on a well, definitely forget about it. Electric works best for small time living/vacation house and where electricity is cheap and reliable and you have 160 amps of space in your 220 amp service panel. Otherwise gas or propane is the way to go.

If one shower stresses my electric tankless to only 22% of capacity, then what prevents a simultaneous 2nd or 3rd shower from being feasible? Or one or two showers plus a dishwasher with a water inlet valve that has a flow-rate limit of 1.3 GPM and that takes less than 1.5 gallons per each of the four or five fill periods that occur spaced apart (much as 20 to 30 mins) through the cycle? Or one shower plus a washing machine?

@dadoes

With all due respect, that information isn't helpful without ALL the numbers.

That would include the size of your system in kw, the temp of your incoming water and the temp of your outgoing water.

The information regarding amount of heat from an electric (and gas) tankless water is heaters fixed by physics and doesn't change by brand. A user considering electric tankless (or gas) should run the numbers with actual gpm and water temps - if possible. Don't go by the assumptions that the tankless manufacturer supply, because they are overly optimistic much of the time. To find the needed temp rise, subtract the water inlet temp from desired temp (105 is the design temp for showers). Then measure how much water your shower uses in a minute.

Electric whole-house tankless are almost always a bad idea. They require inordinate amounts of power at one time and require oversized electrical service. Even at the larger sizes, they provide low gpm output - particularly with low inlet temps. For example, a 36kw heater - one of the largest residential units - will heat about 5.5 gpm from 60F to 105F (shower temp). To put this in perspective, that's 2 showers (2 gpm each) + 1.5 left over - in the summer. If the water gets down to 50 degrees you are at about 2 showers. It takes 160 amps at 220V to provide that - which is massive - just for heating water.

They provide no benefit other than small size, continuous hot water, and ability to locate the heater near point of use. In almost every case except for a cabin, small guest cottage, or similar type of residence, a tank heater would be a better option.