Phoenix propane fueled unit for Radiant and DWH or something else

hillesMarch 24, 2011


We have new construction on a 4500' 5BD 3.5BA 2nd home in Northern California. Our HVAC sub is recommending an all-on-one Phoenix 199kBTU/119g propane-powered DHWH to heat our radiant floors (through a heat exchanger) and provide domestic hot water directly. Our 14 zone radiant is 60% in our concrete floor topping slab, 40% in gypcrete under hardwood or carpet.

Phoenix has only been briefly mentioned on these forums .. curious as to why.

With our PV array, we expect to near zero out our electrical bill at year's end so are reluctant to go 100% propane. I've seen suggestions on these forums to go with a low-mass boiler (Munchkin?) and separate electric DHW.

How much we would lower propane use by separating the DHWH? We may be bumping up against our electrical service ceiling .. not sure what an electric DHW connected load would look like.


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I am shocked that anyone would do PV and be considering electric DHW. You do realize that solar hot water is about 5x the efficiency of PV (it might be closer to 10x)?

I am curious what your estimated heating needs are? Propane matched with PV seems strange to me. Ah - but you are in CA. I guess that might make sense with your electric rates. But please heat your water with solar. I would consider solar for running the radiant.

200k btu seems like a lot. I'm assuming you are at elevation. But even still that seems like a lot. I am in a similar size house and I am under 100k btus and only because a/c drives the sizing here. We get under 10 degrees (but not often).I think man J puts our heating needs closer to 50k btus.

I am similarly surprised that PV makes sense in a second home situation unless you rent. But typical second homes used 10-20% of the time are hard to justify PV even at $.40 a kwh. I'm curious what you get to sell at, because around here we just get $.15/kwh. So even with Fed and state rebates and a subsidized selling market, it takes a good sized southern roof to justify PV (in a $ sense).

    Bookmark   March 27, 2011 at 6:26AM
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