I live in your general area and know SF very well. You're on top of things, the fact that you're redoing the floors makes this the right time to consider radiant heating.

Producing heat from electricity is MUCH more expensive than using natural gas. Some underfloor radiant heating systems are modular and can install quickly, others take longer.

Several of my friends have underfloor radiant heating with imbedded water tubes heated by a gas boiler. The heating effect is more comfortable and more gentle than forced air.

Get HVAC contractor bids, I'll bet that an electrical system is cheaper to install but much more expensive to operate. While it never gets real cold in SF, it never gets real warm either, so you'll tend to heat for more months of the year than elsewhere. Another thing to consider is if you're out of the house during the day and tend to turn your heat down, a radiant system is very slow to raise interior temperature when the temperature is turned back up, compared to a forced air system. It maintains a constant temperature very well but (my friends have told me) the warm up can take hours.

Thank you very much for the input, Snidely. I've actually been asking my friends if anyone knows someone in SF with radiant floors so I could ask how well these systems fit in, in our unique climate. SF is tricky because even in the winter, I find that I will want to heat the house during one part of the day and open the windows wide open to let in the fresh air during another part because even in winter it can go from being frigid cold to t-shirt warm outside in the same day. Do you know if your friends are generally happy with the radiant floors or would they go with a different system given the choice to doing it over?

Thanks again!

I don't share your view about SF weather being unique, much of coastal NorCal is the same. In the city, the incessant breezes over most of the districts provide lots of fresh air. Unfortunately the fresh air is too often cool and damp.

Of the two nearby houses I know, both are about 40 years old. Both are built on slab foundations, not all that common here. One had a leak, maybe 15 years ago, that was a mess to find and fix. The other works fine, it's my friends' house and I'm there a few times a month. They aren't the original owners, they bought the house as it is.

They like it very much, I've had several discussions with them about it since it's somewhat unique. They don't touch the thermostat, leaving it on all the time during the winter. They will turn it down only when they'll be gone overnight, because otherwise the warm up time is so slow. I don't know if the same boiler also produces hot water for their house, that's one feature (called an indirect water heater) that's more common in the colder (and older) parts of the US where hot water heating is very popular.

If you like to open windows for fresh air and then want a relatively fast warm-up afterwards, radiant heating may not be the best choice. What kind of heating does the unit have now? You might get more comfort by spending less on the heating system and using the savings to beef up insulation and air sealing.

If you're set on hot water heating, it might be cheaper and more flexible for you to use radiators.

R19 ceiling and R13 walls doesn't sound nearly high enough even in a mild climate like SF. If you want lower heating bills double those values, esp the ceiling. You could double the ceiling with blown in cellulose for a few hundred dollars.

Radiant floors aren't the right option if you're cold one minute and opening windows later in the day.

Interesting information, thanks.

The house previously had one wall heater located in the center of the house, which was terrible. It was deleted and I am deciding on the new system. I am going through a down-to-the-studs remodel so the insulation was already updated. I could only do R-19 on the roof because it is a shallow, flat roof.

The floor is actually open from underneath so installing hydronic radiant between the joists wouldn't be too bad but I am just not sure if the costs are justified. The quotes I have seen were in the $20k range (does that sound right?) even though this is only an 800 square foot house.

Radiators are an interesting idea. How do those systems work and are they a lot cheaper than radiant floors? Does it require a boiler and all the other equipment that radiant floors need? The house is very small so I was never serious about this because placing the radiators in the rooms gets tricky and there are aesthetic concerns - although I just saw some pretty cool modern ones online.

Thanks for the inputs!

Oh, sorry I missed the part about the new insulation. It's probably adequate under the circumstances, day and night temps in SF as you know are rarely lower than 45 or higher than 65 and are most often in the middle.

It's your house, if you plan to stay there forever and radiant floors is what you want, now's the time. An alternative would be forced air at maybe one-third the cost or less, if there's room for a furnace somewhere. The ducts could be exposed and hung from the ceiling or run along the tops of walls, like you see so often in industrial spaces converted to homes or offices or other space in SOMA, for instance.

Radiators are very flexible and I'm sure a MUCH cheaper alternative to in-floor heat, with many of the same advantages and disadvantages. But perhaps more expensive than forced air, you can get quotes to find out. Personally, I like flat European styles and units that hang on walls (I lived in Europe some years ago). Depending upon how your space is divided into rooms, I wouldn't think you'd need more than 3 or 4 small radiators. Each can be sized for the needs of the room it is in. Small boilers can be attached to a wall, but as with a furnace, you'd need an adjacent space (like a garage underneath or attached?) to allow placement and openings for combustion air and exhaust.

Good luck.

@aramaram I'm also in SF and doing a "to the studs" renovation - exploring hydronic vs electric radiant, if you have any good vendors to talk to that would be greatly appreciated. Or any advice as well.