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Community and Q&A

New house build – hw and heat system choice – cost vs payback?

gordsid | Posted in Mechanicals on

My wife and i are retiring to a new build 1150sqft one level with icf walkout basement (for boat storage and shop space) in zone 6 with a couple snaps at -35c on lake waterfront west facing (windows…windows). We are deciding stickbuilt vs modular and are at the design point of mechanical systems – we are not rich so upfront cost is a real concern.  We have no natural gas and favour electricity for all systems to be inline with the future of energy (diesel backup).  We get that we can upgrade insulation, triple pane windows, , adjustable window shades, icf etc…. to reduce the demand passively at a high frontcost and then choose a hitech mechanical system at a high cost and both together probably are out of our price range upfront…… are we bad people to then say that we will be dead before these costs catch up to less passivity and cheap baseboards at higher electric bills and no maintenance wrt payback? (to be extreme on the low tech side) – so, where is the line of appropriateness in today’s costs vs payback? We dont want to use carbon but may concede to a small wood burning free standing glass enclosed unit (we are in a forest) as a helper and ambience factor.  what to do? heat pump, split systems, sdhv, boiler, conventional forced air,….. sigh (also consider code for return air and fresh air to all rooms required in code….. more cost more sigh). much thanks for any help on finding the affordable – front end cost, operating cost, maintenance cost, lifespan, resale value, payback time, comfort, – lol 

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  1. Expert Member
    Dana Dorsett | | #1

    A usually cost-effective compromise on heating/cooling is to use two half ton or 3/4 ton ductless mini-splits (one per floor) to cover the larger open spaces, with electric baseboard for the doored-off rooms. During the shoulder seasons even into the warmer parts of the winter the mini-splits can cover the ENTIRE heating load using about 1/3 the power of baseboards, and even during the dead of winter any heat it provides would be using only about half. But if your electricity is dirt cheap, and even cheaper at night under time-0f-use rate structures even that might be a "pays never".

    Run a net present value (NPV) calculation of future energy cost savings using the current interest rates as the discount rate. If it's present-value-positive by the end of your (or the mini-split's) expected lifecycle it's "worth it". There are lots of variables about future energy costs, future weather, etc. introducing large error bars when looking decades out, but it's at least a framework that helps get a handle on it.

    With windows, insulation & air tightness issues there are factors beyond NPV that have to be considerered, such as comfort, code minimums, etc. Building to IRC 2018 code minimums (somewhat higher-R than the NBC in Canada) may not be NPV+ within your anticipated lifetime if you're on your third round of cancer treatments or if you have 5 cent electricity, but in most locations it will "pay off" well within the lifecycle of the building, even if leveraging the heating energy use with heat pumps. But building to those minimums is at least going to be somewhat comfortable. An ICF foundation beats IRC code minimum performance requirements even for above-grade walls.

    Then there are the personal values issues. Concrete had a fairly hefty greenhouse footprint, so building the at-grade walls of the walk-out basement could be a "pays never" on a carbon accounting basis if heating with low or zero carbon electricity sources. Even if the grid power is currently high-carb, the carbon content of grid electricity has to come down dramatically within the lifecycle of the house (or even the lifecycle of a mini-split) it the world is going to avoid 2C warming by 2100. Upfront carbon footprint matters now more than ever, since the hit is taken now, and any future carbon "savings" are well into the future, and may even never come to pass. Tuesday's blog piece on this site is instructive:

    https://www.greenbuildingadvisor.com/article/a-better-path-to-a-low-carbon-future

    The referenced white paper using a Toronto for the modeled examples lives here:

    https://gallery.mailchimp.com/e23b9c67f814f1b3b3eb2d741/files/036b0c11-3033-456d-9eb2-895a46e69f32/Buildings_as_a_Climate_Change_Solution_White_paper_2019.pdf

  2. Expert Member
    BILL WICHERS | | #2

    You may want to consider propane instead of diesel for your backup generator. There are several reasons for this:
    1- Most residential generator systems are available for natural gas or propane, but not diesel fuel. Using propane allows you to use more common systems that are targeted for the residential market. I would look at Kohler's units here.
    2- Diesel fuel needs some maintenance. There are issues with watering and algae growth in the fuel. This means that for long-term storage, you sometimes need to have a company come out to "polish" the fuel (dewater and clean it). Yes, this is a real issue.
    3- Diesel engines sometimes have issues starting in very cold weather. The solution to this problem is to run a block heater all the time, but then you're paying for electricity to keep an engine warm all the time even though you might not need it anytime soon.

    Propane does not degrade and has an unlimited life in storage. This is why remote telecommunications sites often use propane fueled backup generators. Propane fueled generators usually only heat the carburetor and not the engine block which requires much less energy to keep the engine ready to go in cold weather.

    Propane also gives you the ability to use a propane fired furnace or other heat source as a backup, assuming you'll be using some kind of heat pump as your primary heat source. I think you'll find propane to be MUCH lower maintenance for your backup power system compared with Diesel.

    Bill

  3. gordsid | | #3

    much thanks for a quick reply Dana - i hear you on the carbon.... and i like your blue collar limits sensibility on where a bit of lowtech is ok - and yes, we are in bc with water based electricity....
    What is your thoughts on the small in-wall duct high velocity system? and does it and the mini splits still need fresh air ducting to rooms?

    1. Expert Member
      Dana Dorsett | | #7

      >" yes, we are in bc with water based electricity..."

      Electricity rates tend to be pretty cheap in B.C. too, which tends to steer the numbers away from higher cost system such a ground source heat pumps or best-in-class fully ducted heat pumps.

      >"What is your thoughts on the small in-wall duct high velocity system? and does it and the mini splits still need fresh air ducting to rooms?"

      Combining ventilation with heating is usually a bad idea, since ventilation requirements don't rise & fall with heat load. High velocity ducted heating/cooling tends to be more expensive and less efficient than ductless mini-split solutions. While the heating distribution is better, if your backup on the remote rooms is hydro powered baseboard on a mostly-hydro grid it's hard to make the case for that approach.

      In new construction it's possible to make the house net carbon negative ( net sequestered-carbon rather than a carbon footprint) if you have full control over the materials choices. In conventional stick built construction it's hard to beat cellulose insulation & wood siding. I'm not sure if MSL's SonoClimat Eco4 insulating fiberboard sheathing is an option near you (it's made in Quebec), but it too would be net-carbon negative insulation and has reasonable structural sheathing capacity. With a walk-out basement there's no avoiding some amount of embodied carbon footprint in the foundation & walls, but that too can be engineered to be less than typical standard practices.

      These sets of slides from the last NESEA conference (covering some of the same stuff in the white paper) can be useful for shaping your approach to embodied vs. sequestered carbon. This is even more important in your case, since the carbon footprint of YOUR energy use in an all-electric house is very small compared to the typical which makes the up-front CO2e far & away the dominant lifecycle carbon footprint of the house.

      http://nesea.org/file/22951/download?token=fMweHJwB

      http://nesea.org/file/22952/download?token=rOjJ2VNV

  4. m854 | | #4

    I was going to suggest more reliance on burning wood, but it turns out it's more complicated than I thought. In theory burning wood is carbon neutral. But done on an industrial scale it probably isn't, unless it's done with wood that would otherwise be wasted, or unless the forests are carefully managed. https://www.smithsonianmag.com/smart-news/epa-declares-burning-wood-carbon-neutral-180968880/

    If you can harvest fallen and dead trees on your property I think it would be a reasonable option. But it's a huge amount of physical work, and that might be hard after retirement age.

    I also wouldn't suggest wood in an urban area, where even an efficient EPA certified woodstove will make enough pollution (mostly particulate, I think) that it would be a problem if most people did it.

    1. Expert Member
      BILL WICHERS | | #6

      The big downside to burning wood is you get all kinds of nasty stuff coming out and not just CO2. CO2 is really pretty benign, but a lot of those other "nasty" things aren't. If you do burn wood, you need to use one of the gasifiers to keep emissions down (I think the EPA regs are gradually making gasifiers the only permissible option for wood boilers), but they cost a lot more.

      It's like I like to say: it's the SYSTEM you need to think about, not just any one particular aspect of that system. One of the big advantages to natural gas (or propane) is that they burn clean, pretty much just CO2 and water as combustion byproducts. Burning wood releases all kinds of other things, many of them FAR worse than CO2.

      Bill

  5. gordsid | | #5

    i bow to your propane benefits Jim - thankyou

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