Advice on water heaters and air sealing
I am building a two-story house, 24 X 40'. The 1st floor is below grade on 2 sides (poured concrete with 3" of Roxul below grade and 4.5" covering any above grade concrete)) and exposed to the south and east . All walls above grade are 2 X 6 sheathed with 1/2" CDX (semi-advanced framing using double top plates) to be filled with cellulose and covered with 3" of Roxul. The roof is to be made with 2' heel trusses to allow 2' of blown cellulose insulation.
The first floor is to be heated via radiant floor system 1/2 pex in a 6" thick slab sitting on 4" of Blueboard with heating supplied by domestic water heater (I wish I had read more GBA blogs before this was poured e.g. excessive thermal mass and perhaps not the most efficient system, but the slab is poured and pipe in place).
I live in central Virginia in the foothills of the Blue Ridge Mtns with winter sun hitting the house from 9am to 4 pm. My widows are mostly south-facing with appropriate overhangs for my latitude. I will have a wood stove (with exterior air intake) on the first floor, I hope to have 2 chases with appropriate fans to draw air from the 2nd floor down to the 1st and install grills in the interior doors to allow airflow. I will install a dehumidifier probably a Santa-Fe, on the 1st floor for summer humidity and have an Tamarack attic fan (not to be used at the same time). I plan on using passive ventilation with bathroom fans and kitchen ventilation run by humidity sensors.
Right now I have just finished the exterior framing and am awaiting the trusses I mentioned. I work full time and am building part time and paying as I go.
1) Is a hybrid heat-pump/resistance water heater worth the expense as I would only use the heat-pump 6-8 month out of the year as this is one of my heat sources during the winter?
2) What would be a good air-sealing approach as I am building slowly (tape the plywood, Tyvek only, caulking interior wood joints before insulation is applied, air tight drywall, or some hybrid)? I plan on using Tyvek under the Roxul and addressing this along with siding/flashing/ windows, one wall at a time.
Posted Thu, 08/15/2013 - 23:52
Edited Fri, 08/16/2013 - 05:14
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