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HVAC conundrum

user-7327173 | Posted in Green Building Techniques on

Hi Everyone,
I live on the Central Coast of California in a 1905 2 bed/1 bath house with a natural gas furnace in the wall in the living room. I’m going to add a bed and bath totaling 450 sq. feet and am looking at different HVAC options. There’s a fireplace that will be closed off, as it doesn’t work, and I’ll be adding spray foam insulation in the attic and under the floors, even though it rarely drops below 45 and rarely goes above 93 here. The old single pane wood windows will remain and I plan to add inserts to seal off the drafts.

So, I’ve hired a local energy advisor who likes the idea of adding a Sanden water tank and hydronic baseboard heating, but then I wouldn’t have any cooling. It would also require me going back to the architect to figure out a place for an 80-gallon water heater (I currently have a tankless system). I’ve been holding off on filing all the permits until the HVAC question is resolved.

I like the Unico system for the looks. There’s just one contractor about 1 hour away who does those installs. Spacepak isn’t available here. I’m thinking about adding solar within 2 years, and so I’m leaning toward a heat pump rather than doing the more economical FAU, but I’m wondering if I’m just going to be wasting money because my house is small and it’s just me and my daughter. I definitely am avoiding the ductless because those heads would look bad in my vintage house. Besides the Unico I’m just wondering in general about ducted systems and how much heating and cooling I’ll realistically need in my house, as the heating and cooling will be going to rooms that aren’t necessarily occupied.


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  1. charlie_sullivan | | #1

    The Sanden is a fantastic product with terrific efficiency for heating and hot water. But I agree that the lack of cooling is a drawback. I'm a fan of the Chiltrix system which is a similar concept but includes cooling. It can be tricky to find a contractor who is skilled with that system, and in particular with dealing with chilled water and insulating pipes to prevent sweating, as well as a designer who can competently spec a system with it. But by the time you are done, either Chiltrix or Sanden will be expensive and a little hard to justify with such a low heating and cooling requirement.

    If the look of mini-split heads is out, consider a "ducted minisplit". A typical installation might be the head of that installed in the top of a closet, with the closet ceiling lowered a bit, and then very short ducts running through the walls to adjacent rooms.

    If you care about global warming, you should be aware that standard closed cell spray foam using a "blowing agent" that is >1000X worse than CO2 for the climate. Fortunately, you have options: you can use newly available "HFO" closed cell spray foam, or you can use open-cell spray foam.

    Under floors is not often a good use of the expense of spray foam--if you have a crawl space, insulating the perimeter of the crawl can be much less expensive for the same energy and comfort improvement.

    1. user-7327173 | | #4

      Hi Charlie,
      Thanks so much for the notes. I'll look closer at the different spray foams available now. I am definitely looking at the ducted mini-splits. My only thought here is that you can't close the vents, right, so I'll be heating and cooling areas that don't necessarily need it. Meaning, 90% of my time in the house is in the living room, I probably don't need to be conditioning the bedrooms, especially the guest bedroom that gets used 1 week out of the year.


  2. Expert Member
    Dana Dorsett | | #2

    Until you actually calculate the loads there is no way to come up with the optimal solution. Hopefully your "energy advisor" knows how to perform a Manual-J, or knows how to hire such a person. Without it you're just shooting in the dark hoping for a bullseye.

    Are you looking for a solution that gets rid of the wall furnace too, or just something for the addition?

    1. user-7327173 | | #3

      Hi Dana,
      The energy advisor will be doing the Title 24 work, as well as the HERS testing. I do have the load numbers provided through Wrightsoft. And, yes, the solution would be house-wide.

      1. Expert Member
        Dana Dorsett | | #5

        ...and the Manual-J numbers are....


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