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Community and Q&A

Please recommend an HVAC system for retrofitting a 2-unit Victorian in San Francisco

Pamela FAULK | Posted in Energy Efficiency and Durability on

Both units in my building currently have natural gas wall panel heaters.

I have available attic space and a mostly unfinished basement area. I am considering switching to some form of solar for one or both units. I’m also looking into heat pumps and high velocity ducting. I’m concerned about air quality, noise and the possible compromise of the historic character of the house. My current electric bill is under 50. per month. My gas bill increases by about 50 per month in each unit in the colder months. It seems like solar is still too expensive in that I’m also looking at the expense of additional insulation and heating appliances. I would like to use whatever insulation would provide the best sound transmission reduction between the two units. What would you recommend?

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, I'm not sure what you mean by "natural gas wall panel heaters." I'm guessing either:

    (a) Natural-gas-fired space heaters with through-the-wall venting, or

    (b) A hydronic heating system with wall-mounted radiators.

    I'm also unsure of what you mean by "some form of solar" in reference to space heating. You could be referring to either:

    (a) A solar thermal system that uses solar collectors that circulate fluid, and then uses the warm fluid to heat that house.

    (b) A photovoltaic system that reduces the home's electricity bill.

    Most contractors can recommend ways to reduce sound transmission between your two units. If you have specific questions about which materials reduce sound transmission, you can post those questions here.

    There are lots of different ways to provide space heat. Since your building has access to natural gas, it's going to be hard to beat natural gas for affordability. (Natural gas is an inexpensive fuel.) Our advice will depend on whether your building already has a boiler, or whether you have wall-mounted space heaters.

  2. Pamela FAULK | | #2

    Thanks for your prompt reply.
    The building has wall mounted space heaters, one in each unit located in the hallways where the heat gets trapped in the high ceilings.

  3. GBA Editor
    Martin Holladay | | #3

    I suggest that you contact a contractor to get some bids. Most contractors will probably recommend one or two natural-gas furnaces to heat your duplex.

  4. Expert Member
    Dana Dorsett | | #4

    Running ducts in an old Victorian is sometimes next to impossible, but plumbing in some radiators can usually be done without wrecking the structural or aesthetic integrity of the place.

    Your heat loads are probably within the range of a cheap gas hot water heater based combi heat/hot water system, but is also within the capacity of a small air-source hydronic heat-pump/chiller. Done correctly with sufficient radiation area the thing could both heat & cool at similar efficiency to ground source heat pumps, without duct or blowing air (but wall-mounted coils could also be used, if desired.)

    To get to the "right" solution starts with calculating the heating & cooling loads. Only when you know the load is it possible to zoom in on what makes the most sense. Hiring an energy nerd to run a "Manual-J" load calculation, using fairly aggressive assumptions on the R-values/U-factors would be the right thing to do. IIRC under CA Title 24 rules equipment has to be sized with a Manual-J calc, but when performed by contractors there's usually a number of errors (or thumbs intentionally on the scale), which can lead to some large "garbage-in = garbage-out" inaccuracies, which is why an independent evaluator is a better way to go.

    Since you have a heating history on the place, it's possible to use fuel-use correlated to weather data to put an upper bound on what the heating load is, which would at least be a start. A January-February gas bill with exact meter reading dates and gas quantities, and the ZIP code (for looking up the nearest weather station on, and the input/output BTU numbers on the wall furnaces would be enough information to work with.

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