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Tankless and recapture and solar oh my...

I am getting way ahead of myself here project wise, but it's always fun to plan out the future ;) I have recently moved into a house that has a crawlspace into which I could fit a shower drain heat recapture device. I am excited about this for the relative ease of install here (previous house was on a slab with showers on first floor, not going to happen)! That will reduce costs for hot water for showering, but wont help with the fact that the hot water heater we've got can barely fill the tub if you happened to be washing dishes at the same time. To increase that comfort I'm thinking that a tankless might be the first big purchase but can the 2 work well together? If my water input to the tankless is pre-warmed by the recapture it will throttle back and keep heating right? Or if I send the warmed water up through the cold to the shower will I mix in less and less of the hot water until the demand is too little and it shuts off? Do the newer ones handle varied loads well?

Then in the far distant future I want to capture some of the huge amount of solar energy that falls on the roof just a few feet from where the current water heater is in the attic. but that will need a storage tank. Should I keep the current water heater tank in line before the tankless heater and run the solar loop through that? So that whatever temperature is in the tank the tankless heater will add only enough to bring it up to the set temp until it runs out? Or is that asking too much from the control systems of these devices.

I understand these are vague desires at this point, but I dont want to lock myself out of doing the recapture or the solar in the future by purchasing the wrong tankless now.

Thanks for listening to me wax poetic about future projects!

This is a great site :)


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited February 2011
    Great ideas...

    There is a device that can recover waste heat from the drain line. It is called a GFX Heat Recovery unit. Additional information at http://www.gfxtechnology.com/faq.html

    As for cooling the attic and utilizing that energy in your DHW stream, a bit trickier to do to avoid freeze potentials, but great idea at http://www.solarattic.com/

    If you wanted to consider ripping your old roofing off and replacing the plywood underneath with a very efficient system, consider www.warmboard.com . Again, you will need to use antifreeze to avoid freeze damage, but it would work well with a dark shingle.

    Also, as for the tankless, make certain that it is compatible with preheated water or you will be back here asking about cold water sandwiches...

    Welcome to The Wall. The Worlds LARGEST information resource for hot water and steam systems.


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  • Larry Weingarten
    Larry Weingarten Member Posts: 3,338
    to your question of preheating...

    ... water feeding the tankless heater:  You might simply run the cold supply to the shower through the shower heat exchanger.  This prevents any long runs and feeds the tankless with plain cold water so it is less likely to misbehave.  As the benefit of the heat exchanger is felt in the shower, you simply adjust the mix to use more "cold" water.

    Yours,  Larry
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