Radiant heating/woodstove

Discussion in 'HVAC Heating & Cooling' started by Supervisor, Feb 28, 2012.

  1. Dana

    Dana In the trades

    Jan 14, 2009
    Drainwater heat recovery units of this type rely on the surface tension of the water inside the drain to spread it out into a thin film covering the interior surface of the drain, maximizing surface contact for better heat transfer. That surface tension doesn't cut it against the forces of gravity if you lay the thing on it's side. They make some pretty stubby versions (as short as 18" from some manufacturers), but the total surface area of the center-bore drain counts- fatter & longer ==> higher return efficiency. To get ~50% heat returned at 2.5gpm flow you need about 48" potable wrap built onto 4" copper drain drain, or 60" wrap on 3" drain. Natural Resources Canada maintains a list of models that are third-party tested for efficiency under standardized conditions for apples-to-apples comparisons, and for different levels of government subsidy.

    EFI in Westborough is a US distributor for Renewability ( PowerPipe), but the shortest one they list as standard product is 36" long. (They'll open an account and sell them onesie-twosie quantities over the phone if you have a credit card number, and they don't hose you bad with handling charges on the shipping either.) If that's too long, Renewability has a 4 x 30" that you can order off their website (at a full retail type price, so as not to compete with their distributors).

    There is one vendor with a plate-type HX designed for horizontal apps, but I'd be inclined to think that the clog risk and loss of performance to sludge would be considerable with any plate type system. They don't have any NRCAN-third-party tested units that qualify for Canadian subsidy (yet), and the design seems to be evolving from an expensive all-stainless version from a couple of years ago to something else:

    was: [​IMG]


    From a cost/benefit point of view, the payback on any of them is dead-slow for 1-2 person families heating hot water with natural gas, but for a showering family of 4 heating hot water with propane, oil, or electricity it's a pretty good investment. Since the drain has to flow while the hot water is running to get any heat return, it works great for showers, but not at all for baths.
    Last edited: Mar 8, 2012
  2. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    quote" Originally Posted by Dana[​IMG]
    Pressure cookers are legal in MA, "

    They might be legal today, but by tomorrow, I suspect they may NOT be!!!!!!!!!!!!
  3. Dana

    Dana In the trades

    Jan 14, 2009
    Not even at yard sales... :-(

    I personally know at two people who were close enough to feel the heat of the first blast. Fortunately their bodies are intact, but the pschological bits are still TBD. (One is the mother of a 3 year old, who was gladly at home with her dad.)

    I'm sorry to report that the other drainwater heat exchanger manufacturers don't seem to be listed on the MA Accepted Plumbing Products online listings (not that it would let that stop me from installing a GFX, Retherm or Watercycles or Thermodrain or EcoDrain product- even if it took a variance or a heart-to-heart with the inspector & a note from my mom.)

    It probably doesn't take a huge effort to get on that list though, if the manufacturing & materials are up to code for other locations, but it probably WOULD take a variance to get it approved by many inspectors, who are on the hook if for some reason it becomes a hazard after they sign off on it without higher approval. I'd be pretty happy to see more competition in this market- it's not as if there's rocket science behind the designs. At some point I'd think the price of copper would drive the retail numbers as much as anything, but it's a tiny market with but a handful of players, and they all seem to be sniping at one another.

    It's good to know I have no credibility on this forum though, I was worried that I might actually start making sense or that people might take me seriously. :cool:

    I've never bothered counting my drainwater heat exchanger discussions, does this one count as 201?
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