Update: flap in the foam around the water heater?

[profdant139]

(Edit: SEE OCT 23 POST BELOW FOR SEMI-AMUSING UPDATE)


My trailer is so small (this sounds like the start of a joke, but it is not) that the water heater, by itself, almost puts out enough heat to warm the interior.

So this gives me an idea -- the water heater, which is below one of the dinette seats, is covered in a styrofoam jacket. Ordinarily, that foam is very useful -- it means that we use less propane to keep the water hot, plus it keeps the water heater from overheating the interior of the trailer in warm weather.

But if I could cut a removable flap or opening in the foam, I could get more interior heat from the water heater. It would be a "redneck heat exchanger." I would replace the flap when I no longer needed the extra heat. (At night, for example, we don't really care how cold the interior gets -- we just pile on the blankets!)

So that is my question -- is this idea feasible? Is there some hidden danger that I am missing?

Thanks in advance for your advice!

[BarneyS]

With the OP stating his new, scientific, and novel solution to the problem, it is time to put this thread to bed after three pages of replies. Than you everyone for your participation.
Barney

[Tin_Pusher]

Another happy ending 🙂

[profdant139]

I am sure the tank temp is not over 150. But the real issue is whether I want to mess with the insulation, when DW simply wants a hot water bottle in her lap.

Which, coincidentally, is the solution we've adopted! 😉

[Tin_Pusher]

Wouldn't think the tank temp would exceed 140 - 160 deg F, not likely any fire danger it seems to me. After all, how hot is your water?

[profdant139]

We could use hot tap water, but boiling water is much hotter - we will wrap the hot water bottle in a towel and it will stay hotter longer.

[herbhofmann]

profdant139 wrote:
UPDATE

So, I am getting ready to slice into the foam -- I was all set to create a velcro hinge for my foam flap, to drill into the cabinets for vent holes, yada yada yada -- and I decide (for reasons of diplomacy and domestic tranquility) to check with DW. I drag her outside to the trailer to explain the whole thing.

She nods and says (politely), "Good idea! But how is this so different from a hot water bottle? I could boil water on the stove, fill the bottle, and put it on my lap, under my lap blanket, while we are eating dinner or reading." (That's how cold it gets when we boondock -- we often use lap blankets and wear warm ski hats while we are inside.)

I sputtered a little, disappointed that I was not going to get to do yet another "mod." But she had a point -- yes, it is a little more trouble to boil the water and fill the bottle. And it might waste a couple of quarts of water per night. But it means that the water heater will not have to cycle on and off, I don't have to cut the insulation, I don't have to drill any holes, and the heat is right where she wants it -- under the blanket -- rather than indirectly warming the interior of the trailer.

Darn.

If you are going to use "water heater" heat to warm with, why take the time to boil water? Just use the hot water out of the faucet. Of course, if you are boiling water for dinner, you have it available anyway.

[westend]

JiminDenver wrote:
West
When I first started looking I saw dual purpose panels with a wet side under the PV side. It's what gave me the idea for a coil of hose under the panel you have now. I don't think it'll add too much weight.

Jim, the hose thing might work, I'll test it out in the next day or so.

Since I have a diversion load output on my solar controller and the batteries are completely charged, I'm still thinking of how I can use that potential power. That potential could be 180 watts for 4 hours/day and less during the shoulder hours. If I was going to heat water with that diversion the formula is Kw= gals. x temperature rise (f)/ 375 x heatup time. On a perfect day, I'd probably be able to heat my 30 gal. fresh water tank by 10f rise. That doesn't sound like much but if the water in the tank started at ambient, that would be a lot of stored heat to augment the propane heater. Also, that heat is free, basically, just using the yet unused diversion load available.

Lots of ways to get feline fur. Hitech was investigating using his excess solar to run computers and trade processing time for $$. Not too bad an idea but the payback for the capitol expense was about nine months, in the best scenario.

[JiminDenver]

West
When I first started looking I saw dual purpose panels with a wet side under the PV side. It's what gave me the idea for a coil of hose under the panel you have now. I don't think it'll add too much weight.

[westend]

JiminDenver wrote:
Even without cutting the foam the water heater puts out heat, A few small holes would allow some of it in to the cabin. A small computer fan would help, it just depends on how often the WH fires. Ours in under the bottom bunk and in the summer with the WH on it would miserable to sleep there. Quite toasty in the winter though.

I thought about doing a solar water heater diversified load and decided it would be a lot of money for hot water we don't need later on in the day. With a tank the size of a fresh water tank I think you would be better off with a hot water panel and do it old school. You could even paint a white hose black and coil it under your solar panel, pump your fresh tank thru it and pick up more BTUs than the PV can do alone.

Jim, this is another thing I've thought about, making a solar heater on top of the trailer. The downside is that I'd be adding even more weight to the roof and that isn't a good thing. Who knows, maybe we'll all be looking for portable solar heaters in the future.

[JiminDenver]

Even without cutting the foam the water heater puts out heat, A few small holes would allow some of it in to the cabin. A small computer fan would help, it just depends on how often the WH fires. Ours in under the bottom bunk and in the summer with the WH on it would miserable to sleep there. Quite toasty in the winter though.

I thought about doing a solar water heater diversified load and decided it would be a lot of money for hot water we don't need later on in the day. With a tank the size of a fresh water tank I think you would be better off with a hot water panel and do it old school. You could even paint a white hose black and coil it under your solar panel, pump your fresh tank thru it and pick up more BTUs than the PV can do alone.

[profdant139]

UPDATE

So, I am getting ready to slice into the foam -- I was all set to create a velcro hinge for my foam flap, to drill into the cabinets for vent holes, yada yada yada -- and I decide (for reasons of diplomacy and domestic tranquility) to check with DW. I drag her outside to the trailer to explain the whole thing.

She nods and says (politely), "Good idea! But how is this so different from a hot water bottle? I could boil water on the stove, fill the bottle, and put it on my lap, under my lap blanket, while we are eating dinner or reading." (That's how cold it gets when we boondock -- we often use lap blankets and wear warm ski hats while we are inside.)

I sputtered a little, disappointed that I was not going to get to do yet another "mod." But she had a point -- yes, it is a little more trouble to boil the water and fill the bottle. And it might waste a couple of quarts of water per night. But it means that the water heater will not have to cycle on and off, I don't have to cut the insulation, I don't have to drill any holes, and the heat is right where she wants it -- under the blanket -- rather than indirectly warming the interior of the trailer.

Darn.

[westend]

profdant139 wrote:
westend, a heat exchanger with a fan would be more effective. But also more work! (And the fan would use a little electricity and would make a little noise.) I am trying this halfway measure just to see if it works at all. If it does, maybe I will try something more elaborate -- maybe an old-fashioned radiator??

Yup, no free lunch, lol.
Forum member smkettner, along with others, have blazed the ground with hydronic heating. I am considering it as it's very efficient and quiet. I haven't pursued it seriously since my furnace/heater is silent and operates at fairly low consumption. I'm also thinking of stretching out my solar output, using a heating element in either the water heater or my fresh water water tank. I have a steel tank so am able to store quite a few BTU's in that tank.

Just with a few minutes searching: Heat exchanger $18. 120 mm computer fan $10. Misc. plumbing and wiring may push this project North of $50, might be worth it. This assumes that a pump won't be necessary because the exchanger is close to the tank and there will be circulation from heat differences.

Good luck with the passive model, it may be just what you need.

[profdant139]

Larry, that is a good point about the heat rating of the foam! I probably would not use the spray anyway -- too messy, and it would stick to the tank. And Gjac, you are right that this is not a free source of heat -- but I have propane to burn, so to speak!

[Gjac]

I think you have a good idea. It would save the main batteries and probably be more cost effective than a Buddy type heater. Also I would consider cutting a 4 in hole in the dinette seat vertical wall and installing a computer fan to distribute the heat once you have determined enough heat is coming off of the HWH. Just be aware that you are not getting free heat but the savings will be in battery power and using a cheaper source of propane than those little bottles.