Hi Jay, I agree with Brad that Evacuated tubes are not a good (or even a reasonably possible) candidate for a drainback retrofit. If they are pass-through tubes, then they cannot fully drain as piping connections typically come through header connections at the tops of the tubes. If they are sealed heat-pipe tubes, then not only is the header unlikely to drain properly, but the tubes themselves will stagnate at a very high temperature without heat transfer fluid flow.
I recommend a diversion heat- dump arrangement such as Todd suggests.Use paralleled runs of conventional hot water baseboard fin tube for the heat dissipator. This stuff is readily available at almost every plumbing supply house and it works well. Diversion can be activated by either an electric 3-way valve and a set point controller, or the passive wax-thermostat 3-way valve that you mention. I have used both methods extensively with good results. The wax thermostat will probably be significantly harder to find. Some years ago I ordered them through Low Energy Systems in Denver. Reach out to me off list and and I can supply some contact information. -Luke Luke Christy Renewable energy consultant NABCEP Certified PV Installation Professional™: Solar Gain Services, LLC PO Box 531 Monte Vista, CO 81144 719.588.3044 sgsrenewab...@gmail.com > On Jun 17, 2025, at 3:46 PM, jay via RE-wrenches > <re-wrenches@lists.re-wrenches.org> wrote: > > In doing research today I found the following, not sure where I can buy them > at this point. > > 1. solar dissipation tubes. that will do about 12,000 btu or at least this > one does. > > 2. 3 way thermostatic valve which uses a type of wax that opens and closes it > at a specific temp and routes the heat through the dissipation tube vs the > heat exchanger down below. >
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