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Community and Q&A

The Cost/Benefit of Energy Upgrades

aztecrsf | Posted in Energy Efficiency and Durability on

Greetings GBAs…

We’re building a home in coastal San Diego next year, and I really want to ensure energy efficiency and comfort. We’ve lived in a “cold” home before — yes, cold in balmy San Diego — and it was awful. No reasonable amount of heat could make the house feel warm from Nov-April, until I put in a superhuman effort to seal up a crazy amount of holes in the attic, insulate knee walls, etc….stuff that you wouldn’t believe in a house that was mostly rebuilt in 2005.

I get the basic concepts of efficiency. Seal, insulate, passive solar. We’ve done about all we can for designing passive solar; it’s essentially a two story box on a typical small lot, no room for rotating the house at all, but at least we have a good southern broadside with a decent amount of glazing. The north side has barely minimal windows. For sealing, I plan to spend a lot of time caulking/foaming up every penetration and along the sills before drywall goes up.

Insulation is where I start to wonder about cost/benefit. We won’t really have much attic access, mostly vaulted ceilings with 10″ joists/rafters. I figure spray foam for that. Walls? We could do deeper framing to get above R-19, say 2×8, but given the now high cost of lumber, perhaps using spray foam in 2×6 walls would net us more R value more cost efficiently? Or am I overthinking it entirely given the climate?

Then there’s HVAC. We’ll likely have solar, possibly a Tesla roof, so our crazy expensive SDG&E electricity becomes less of a problem. Well, outside of May through August when solar production at the coast is grossly overestimated!  But that’s also conveniently when we likely don’t need any heat (or cooling). So a heat pump seems like a better idea than gas furnace. I’m not very concerned about cooling given ocean breezes and the high likelihood of it being sunny (solar) when hot.

For water heating, I had been thinking on-demand gas heaters near the kitchen and bathrooms. But if I’m generating enough electricity, I’m wondering if an electric tank with an on-demand recirculation loop would be better.

One downside to all this electric stuff is… grid unreliability/vulnerability. So backup batteries. But I cringe at the thought of the environmental impact of manufacturing those batteries when they’ll get used so little (hopefully). I’m tempted to plumb in a natural gas generator for that. However, going into the doom scenario for a moment, gas might be out in a quake, while batteries would be fine. I digress.

What cost/benefit no-brainers am I missing? Thanks for any ideas and comments.

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  1. paul_wiedefeld | | #1

    Solar + right sized heat pump + electric water heating is an established path to low emissions. I think the high wall insulation levels are overkill for this climate, so focus more on the above and air sealing. Skip natural gas for heating and water heating, consider ditching it for cooking too. With your electricity rates, it’s more expensive not to install solar, so the cost of all the improvements is minimal, as furnace +AC is about what a heat pump costs. Think hard about electric reliability and if that’s actually worth insuring against in San Diego (ie I wouldn’t spend 5 figures to possibly save a fridge’s worth of food but other electric loads might be worth it).

  2. Expert Member


    It's an odd paradox isn't it - we seem to slightly underbuild in every climate. I grew up in cold Eastern Canada but was never as uncomfortable inside as I have been when I lived in Britain, or here in the mild PNW. Fortunately when I Iook back, almost all of that was due to air-leaks and single glazed windows, so the solutions houses anywhere should get will work well where you are.

    Houses in temperate places perform better when there is an architectural response to their climate. Here in the PNW that is things like covered outdoor spaces, lots of light brought into the interior from above, and deep overhangs. I would explore what the appropriate responses are to yours and incorporate them into the design.

    As Paul said, I wouldn't go beyond the typical building assemblies commonly used, but rather make sure they are executed well, and concentrate on the sources of heat and energy used. Heat pumps are not only very efficient, but future-proof your house. Solar, especially in your electrical market, also makes a lot of sense to invest in.

    Living on the highway with the most power outages in BC I'm a little more sympathetic to the desire for a back-up source. The most common solution here is a propane or natural gas generator, which supplies you light, heat and cooking on a barbecue, while still leaving the house all electric when power is restored.

    I'm still on the fence on heat pump water heaters. A well performing conventional one, like the Rheem Marathon might be a good choice.

  3. Expert Member
    BILL WICHERS | | #3

    Don't install batteries. Batteries are a big maintenance issue and a big cost. Yes, the newer lithium style are better in that regard, but there are still issues. If you do install batteries, I STRONGLY RECOMMEND installing them in a fire rated room, ideally more than a 1 hour rating. This isn't normally done on residential projects, but I think it's a big improvement in safety. Lithium batteries especially are a big fire risk, and while rare, a lithium fire burns like gangbusters, and is very difficult to extinguish. I would build a 2 hour room (double layers of 5/8" drywall on both sides of the studs), install a fire sensor in there that triggers a fire alarm in the main house, and I'd provide for ventilation to the outdoors for the room.

    Ideally, just go with a peak-shave solar system, with no batteries. Use a generator for backup power. A typical line interactive battery is only going to give you about a day (if that) of backup power, or less for a large home. A natural gas fueled generator is a better option for backup power, especially if you anticipate long-duration power outages (more than a day or so).

    If you can fit in enough solar for water heating, then an electric water heater makes sense. If you can't fit that much solar, then I'd go with an on-demand gas fired water heater. I would heat with natural gas too unless you want to use a multisplit system. Central heat pumps are a good option to, and if you're in a milder climate, they'll probably be able to provide all of your heating needs, so no need to worry about expensive electric "auxillary" heat on those extra cold days.

    If you won't be able to do all your water heating with excess solar power, and you expect to be heating your home much of the year (instead of cooling it), then a heat pump water heater is probably not the best option since they work by robbing heat from the home. That "heat robbing" actually helps you during the cooling season, but during the heating season it's less efficient than just heating the water directly. If you think you'd be in that situation, then an on-demand gas fired water heater is probably your best option.

    BTW, I entirely agree with Malcolm that it's imporant to do a good job putting the place together. That is especially true for air sealing if you want comfort. This is where attention to detail during construction is very important.


  4. Deleted | | #4


  5. user-6184358 | | #5

    Go on the San Diego Green building tour tomorrow
    See what others have done

    1. Expert Member
      MALCOLM TAYLOR | | #6

      Great idea. Looks fun.

    2. aztecrsf | | #8

      Bummer, I missed that. But I did spot that Aerobarrier link for one of the homes. That sounds a whole lot better than me running around with foam and caulk!

  6. steve_smith | | #7

    As far as concerns about electricity reliability and the need for batteries versus a natural gas water heater and furnace, consider that almost all newer natural gas appliances won't work without electricity. Natural gas isn't better in that regard. If anything, the heat pumps all for better load shifting. With the right heat pump water heater, you can set it up to only run when the sub is shining on your solar panels. I'm a bit north of you in the Inland Empire and have been pricing batteries. I don't think they are quite there yet for most Californians with a grid connection, but I'd leave space in the electrical panel and decide where you'll put the batteries in 5-10 years.

  7. aztecrsf | | #9

    Thanks, all, for the comments. I'm glad to see the emphasis on ensuring the "standard" construction is done well, rather than going to thicker walls, etc.

    Zephyr7, excellent point about battery fire risks/consequences. I have a good spot for the batteries that would be easy to 2 hour fireproof (a utility room). That said, I like the idea of a plumbed natural gas generator for serious blackout mitigation during a time of low/no solar production.

    Steve_Smith, the only price info I have on batteries comes from the Tesla roof package, where a modest amount is included. The roof + batteries look to be roughly the same as conventional roof + solar. Of course this assumes Tesla's estimate tool is accurate, AND that they can actually install it when I need it.

    Malcolm, true about that paradox. It applies to much more than building! In CA I think so much construction took place at times when energy was just dirt cheap. Plus, until recently, almost no one ever knew what to look for in a building that would indicate its comfort, and you don't get to test a house by living in it awhile first (unless you rent to own or something). Developers/builders didn't have any incentive to spend $ on ensuring tight, efficient buildings...and so they sure didn't. All the remodeling over the last booming 20 years or so can't have helped either.

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