Bob the Builder Posted May 20, 2023 Share Posted May 20, 2023 Just curious, has anyone tried running water through a flat coil of pex tubing on the roof and circulating it through the water heater during the day so as to have water already heated in their hot water heater when they stop at night for a shower, etc? Quote Link to comment Share on other sites More sharing options...
WME Posted May 20, 2023 Share Posted May 20, 2023 (edited) Ya mean something like this...https://www.ebay.com/itm/403825171004?hash=item5e05db1a3c:g:dkgAAOSwzLpi80Wa&amdata=enc%3AAQAIAAAA8EsXCGvB3foDvNY6Uw%2BX8QVLHepIIEm9heT5n52vfajjAp4uQWPnsYnnTck6HglTSHNY5RwQj9B3xtZnsR1lM1yvw2FgsQPr3rToSbIpQHCjlSTIglJmsK%2F3XhNE7hTOjw4MnTLAx%2BPuzmH%2FFgccIRuGpE61lOPAYirq%2F5XtiZ8y%2F2nlE8s6tcfBO%2BABki3DcjbPNEJNMT6RkAnFoRw1CWW45cy%2FJxuoqxie2qiFJz2B6koikiTHll2aPuqWh5c1e9lPw2xUDnl0dTI%2Bcy5cxTy5Exw26Xn8Fak5hm0ZfDDhB%2FeoEqHWjhgw5oD5y0dZVQ%3D%3D|tkp%3ABk9SR8qC7euGYg It is only going to add a gallon of hot water but will help reduce propane use If you DIY something don't forget Solar on the roof. Edited May 20, 2023 by WME Quote Link to comment Share on other sites More sharing options...
Bob the Builder Posted May 20, 2023 Author Share Posted May 20, 2023 Yep. I was thinking a coil of pex, paint it black, laying flat in a flat frame laying on the roof under plexiglass to keep wind off of it and a small fountain pump or similar with valves to circulate entire hot water heater volume slowly through it. Would probably heat all of the water enough for a shower or so when you stop for the day. Three-way valves to control flow through system normal or through roof solar heater. Panel to run little pump. Keep it low and no wind resistance to speak of. Quote Link to comment Share on other sites More sharing options...
linda s Posted May 20, 2023 Share Posted May 20, 2023 It sounds like a lot of work for not much energy or time savings. The water in your heater and your fresh water tank are already at ambient temperature, so your heating 70 degree water, summer, to 98 at the most. A standard 6 gallon gas water heater should be able to accomplish that in about 15 minutes. Light it when you stop and by the time camp is set up it's hot. No more holes in the fiberglass roof and less stuff to break. Simple is always better Linda S Quote Link to comment Share on other sites More sharing options...
fred heath Posted May 20, 2023 Share Posted May 20, 2023 (edited) I saw a rig a long time ago that had several copper heater cores connected in series on the roof. Owner painted them flat black. Not sure what was used to circulate the water, but he seemed very happy with this setup. Edited May 20, 2023 by fred heath Quote Link to comment Share on other sites More sharing options...
Bob the Builder Posted May 20, 2023 Author Share Posted May 20, 2023 With my bare to the walls shell, I'm starting with nothing. I do not plan on carrying any propane for anything, so I'm relying on alternate methods for heating the water. In my other little camper I had a 7 gallon water heater and ran a 2000 watt gen or shore power for heating the water. It is sufficient, I'm just looking for a possible alternate to that. Using the coils like I'm describing has been proven to heat the water from 70 or so degrees to start up to 140 passively depending on your volume. I'm just curious as to what the 7 gallons could be heated to with a coil on the roof and traveling for the day. It's the overnight stops enroute to somewhere that I'm trying to not use the gen for. Too much going on with the build right now, but was garnering info in case it was worth plumbing for it. Keep the ideas coming and thanks to all. Quote Link to comment Share on other sites More sharing options...
linda s Posted May 20, 2023 Share Posted May 20, 2023 OK I get it. Problem is with volume. 100 feet of 1/2 inch pex only holds one gallon so you're going to have to be actively heating up a tank during the day. You're also going to need a solar, 12volt pump to move the water and it needs to be strong enough to handle the rise. A pump can only push water up so many feet. I made one of these to help heat my hot tub. Didn't work, needed to go much, much bigger. On the roof of a trailer " much bigger" might be a problem so that's why I suggest a tank. Have no idea what kind of tank to use. Linda S Quote Link to comment Share on other sites More sharing options...
Bob the Builder Posted May 20, 2023 Author Share Posted May 20, 2023 Yep, looking to heat up approx 7 gallons or so. One quick shower's worth will do. Using the hot water heater for "tank" during the day. A 12 volt fountain pump is fairly low volume and will pump 3 meters of "rise". I'm thinking how ever many feet of pex will coil flat in maybe a 4ft x 4ft square flat frame on top, painted black, and under an acrylic top surface to keep the wind off. Should only stick up an inch at most on the top. Just an idea, lot to do before then. I will probably plumb in the inlet/outlet, cap off and revisit when the big build is done. Thanks Quote Link to comment Share on other sites More sharing options...
WME Posted May 20, 2023 Share Posted May 20, 2023 Propane is energy dense, 91,000 btu per gallon or 27 kWh per gallon. Solar isn't near as dense. SO maybe a bigger water tank, Get a 5 gallon tank insulate it and circulate your solar hot water through it. The tank would act as a preheated going in to your actual water heater. Then you could have 2 showers a day Quote Link to comment Share on other sites More sharing options...
Maineah Posted May 20, 2023 Share Posted May 20, 2023 I'll never swap out my propane water heater it's fast enough, it's hot and yes get over a long hot shower in any camper! There is just not enough room to make it much better. Both my Toy home and the camper will recover during the night for plenty of heat for a bed time shower and even dishes. They make flash heaters they suck up propane and are wicked noisy. Quote Link to comment Share on other sites More sharing options...
linda s Posted May 24, 2023 Share Posted May 24, 2023 So Bob, the hardest thing to find when making the passive solar thing I made was the right size container. This would be perfect for you. Not cheap but the light weight, about 15lbs, is important. https://seresag.com/products/active-aqua-low-rise-flood-table-black-4-x-4?currency=USD&variant=41015383162937&gclid=CjwKCAjw67ajBhAVEiwA2g_jEPzwOGC6dhx3qe9uZaNbZanXCtJ-9Z3v-s8DeQtzLP6UOntuuNfdqBoCfwoQAvD_BwE From your other posts I already know you can build just about anything Linda S Quote Link to comment Share on other sites More sharing options...
mpanzar Posted May 24, 2023 Share Posted May 24, 2023 you could wrap a copper tubing around your exhaust for a cheap heat exchanger. Quote Link to comment Share on other sites More sharing options...
extech Posted May 24, 2023 Share Posted May 24, 2023 yea and add a check valve and let the heat do the circulation Quote Link to comment Share on other sites More sharing options...
mpanzar Posted May 24, 2023 Share Posted May 24, 2023 Regarding the pump for the solar dome, if pumping to the roof and assuming the water will come back down to the pump level, head is reduced significantly. The caveat is that the pump must have enough power to overcome the initial lift or priming . Once the water is on the downhill side it will begin to pull vacuum and head loss will be reduced. I believe the pipe system is better than a tank system in this case. you'll have better baffling with a pipe system, the CG of the system/camper will be lower, and it should be less weight on the roof. My personal opinion is that the effort is not worth the heat output, id boil a pot of water and add it to some ambient temp water. Quote Link to comment Share on other sites More sharing options...
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