Gas tankless water heater for hydronic heating - San Francisco

vicsj

We are remodeling our house in San Francisco. Title 24 and the San Francisco city's regulations are not clear to me. My understanding is the City building code has a heating requirement for all habitable space. Has anyone installed hydronic heating in their house? Do you know if the city allows gas tankless water heaters for hydronic heating? Any advice greatly appreciated.

Larry Weingarten

Hi, You'll likely find people here think using a domestic tankless heater is not a good idea for space heating, for many reasons. I'd begin by doing a heat loss calculation to see what's needed. Some sealing of air leaks and maybe insulation can help. Alan Forbes @Alan (California Radiant) Forbes would be a good one to contact to see if he can help you do it right.

Yours, Larry

Alan (California Radiant) Forbes

I see tankless water heaters used for hydronic heating, but they usually don't last long because tankless heaters like a large ΔT, otherwise they short-cycle themselves to death.

But to answer your question, I don't know if SF allows tankless water heaters to be the heat source for hydronic heating. I would call the plumbing or mechanical department before proceeding.

Some tankless manufacturers will void their warranty if their product is used only for hydronic heating. They will keep their warranty if used for both hydronic AND DHW.

Jamie Hall

First question is -- does San Francisco even allow new naturel gas hookups or appliances at all?

EdTheHeaterMan

Second question is -- Do you really want to live in California, let alone San Francisco?

As far as Tankless DHW heater for use on a closed loop system, I would not recommend it. Get a Wall Hung Mod-Con boiler. That is what they are designed for. The control system is different that that of an Open System tankless water heater.

Otherwise you will be back here asking: why you can't get it to work properly

vicsj

Thank you everyone for your advice. Our house is small and space is limited. If there is a space saving alternative, please let me know. Thank you.

EdTheHeaterMan

You might want to look at these products. Some will heat two rooms if placed on the adjoining wall. Other's have a vent thru an outside wall. Many are thermostat equipped. some even operate when the power goes out.

https://cozyheaters.com/direct-vent-wall-furnace/

vicsj

Thank you Edward. I considered these before but city regulations require an offset from windows, so it does not work for us.

hot_rod

Do a heat load calc first, then you can start exploring options.

Larry Weingarten

Hi @vicsj , @Jamie Hall brought up a good point. Unless you plan on selling soon, gas will likely be thought of as a negative. You might want to look into heat pump technology. There are mini-splits and other, under the window technologies in addition to the air-to-water approach. Redwood Energy has put together some resources here: https://redwoodenergy.net/research/ Also the Building Decarbonization Coalition has put together some resources here: https://www.buildingdecarb.org/for-design-teams.html

Yours, Larry
ps, another good article on this just came out. It's written by Allison Bailes: https://www.energyvanguard.com/blog/1-reason-have-all-electric-home

JakeCK

San Francisco seems like such a mild climate to need a gas boiler or furnace. Like Larry said above research heat pumps.

Do you even see sub 32f there? If not you could get a monobloc unit and not even have to worry about freeze protection. Honestly I would strongly consider the smallest mini split possible. 

vicsj

Hello everyone, I looked into getting mini-splits, but the cost of installing air handlers in each habitable space (living rooms and bedrooms) add up. We also have a 2 story house with flat roof, so I was told we will need a condenser on the roof for our upstairs. That is not ideal when it comes to repair/maintenance. Not to mention penetrating the roof for the refrigerant lines and control cables. I sincerely appreciate everyone's input.

Hot_water_fan

@vicsj Hydronic heating isn't a great fit for this application because you're in a mild climate, small house, and AC might be desirable. Hydronic heating would require fitting pex throughout the house - instead of that I'd add ductwork and add a central heat pump (notductless minisplits).