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Discussion Starter · #1 ·
Hi All,

As I've been floor planning i've realized the isotemp is going to be hard to fit with our current design. The actual dimensions are fairly small (22in x 12in OD) and I was wondering if anyone had mounted it under their van with a shield or something to protect against road debris.

I've read about the thermostat being an issue and I realize I'd have to crawl under the van to reset it (though there is a resettable thermostat?)

Other than that, is this feasible? I don't have my Promaster yet to go out and measure...
 

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The thermostat is only a thing if you want to use electrical to heat the water. But it is indeed a thing. When heating via the heat exchanger, the water gets so hot that it trips the reset every time. Doesn’t affect heat exchanger heating, but you have to push the button if you want to heat electrically. Maybe it could be remotely mounted?
 

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Discussion Starter · #4 ·
It can be done, but I would go beyond a shield and build a sealed box to keep out road salt/rain slush/etc.
I'll have to see what my options look like. I've seen people mounting propane tanks undercarriage so I'm assuming it can be done.

I feel like it is a lot easier to run cold + hot water + electrical than running coolant lines....

Although then I have to worry about the water tubes freezing. So maybe not a good idea.
 

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I'll have to see what my options look like. I've seen people mounting propane tanks undercarriage so I'm assuming it can be done.

I feel like it is a lot easier to run cold + hot water + electrical than running coolant lines....

Although then I have to worry about the water tubes freezing. So maybe not a good idea.
You technically would t have very much water line below the van. Would be easy enough to wrap with a heater pad if needed. Also - that ish gets HOT! So I’m not sure freezing is even a real concern as long as it’s not sitting for a long period.

another benefit of under mount is keeping those hot coolant lines out of the van space. I’m in Florida, and my heater is inside - it noticeably warms the space and my large fresh water tank during the summer. It gives off quite a bit of radiant heat. All of the brass fittings are like 250 degrees.
 

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Discussion Starter · #7 ·
Literally exactly what I was looking for. Saved in my ever expanding spreadsheet of items and install tips.

Not sure how it'll fit beneath the promaster but some awesome tips here.
 

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I share the concern about dirt and road debris. These things are not designed for outdoor conditions. The electrical box is not water tight and the mixer/relief valve will not be happy caked with road dust.

Running coolant lines is actually no worse than water lines, maybe easier since coolant lines are low-pressure and connections only require hose clamps. I ran coolant lines under the van all the way back to my Isotemp over the rear axle. It was relatively easy. No freezing worries either.

Isotemps do radiate a lot of heat. I wish I had gone with a 4gal instead of 6gal for that very reason. Still, the extra heat can be nice sometimes. Mine is under the bed, in the garage space. It really stays warm under there.

After a coolant-based HWH, a propane-fired instant (on demand) HWH would have been my second choice. There weren't many of those back then. There might be more now. It also depends on how you camp. If you are always on the move like me, a coolant-based HWH works well. But if you plan on parking for several (3+) days at a time without shorepower, it makes a lot less sense.
 

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I share the concern about dirt and road debris. These things are not designed for outdoor conditions. The electrical box is not water tight and the mixer/relief valve will not be happy caked with road dust.

Running coolant lines is actually no worse than water lines, maybe easier since coolant lines are low-pressure and connections only require hose clamps. I ran coolant lines under the van all the way back to my Isotemp over the rear axle. It was relatively easy. No freezing worries either.

Isotemps do radiate a lot of heat. I wish I had gone with a 4gal instead of 6gal for that very reason. Still, the extra heat can be nice sometimes. Mine is under the bed, in the garage space. It really stays warm under there.

After a coolant-based HWH, a propane-fired instant (on demand) HWH would have been my second choice. There weren't many of those back then. There might be more now. It also depends on how you camp. If you are always on the move like me, a coolant-based HWH works well. But if you plan on parking for several (3+) days at a time without shorepower, it makes a lot less sense.

Thanks for the @SteveSS

While being in hot environments I have thought of the additional heat escaping HWT into the already hot van.

I have thought of the propane (on demand) HWH instead of a "Hot Water Tank" HWT. Since all we have is a sink it makes sense.

My only concerns about going with an instant(ish) on demand propane are;

1) Water conservation on board - depends how well they work (ie how much cold water gets wasted down the drain waiting for "instant hot water)
2) Where / How the intake and exhaust for the combustion of propane is handled (prefer floor penetrations rather than wall).
3) That the equipment just works without being finicky


This is on my radar for my new build. If you know of or come across any such on demand propane equipment that looks good to you I am "all ears" or "eyes" in this case. Please post any gems you come across - much appreciated 👍
 

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I have a propane instant(ish)/on-demand water heater in my Airstream, and it’s a love-hate relationship. I have the PrecisionTemp, which comes in a floor vented version.
What bothers me about it in the 26k Airstream might not be a big issue in the van, due to shorter water lines.
  • Hot water takes some time to get to the farthest faucet In the kitchen. My shower gets hot much faster. Might not be an issue in a van, but if it is perhaps you can collect the water and pour it back into the fresh water tank.
  • PrecisionTemp RV-550 NSP vents through the floor
  • in 3 ½ yrs of full time living in the Airstream it has performed without problems. The burner turns itself on for a little while when temps go below 38° or so to prevent it from freezing
  • it can be finicky to mix the proper temperature. I’m about to change my shower fixture from one handle to 2 separate hot and cold handles so that I can mix the water better. The hot water should be fully open and you regulate the temp by adding cold water.
I have been eying the Truma systems for a while now, but they are even more expensive than the PrecisionTemp. Truma makes a combination cabin/water heater. It’s a German company with an excellent reputation.
 
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IIRC, it's possible to add a cold return at a faucet to divert the initial cold stream from a HWH back into the fresh tank. I think I first heard about it years ago on FitRV.com. I've seen it mentioned other places, too. Try Googling "RV cold water return". My IsoTemp is only a few feet from the faucets. I maybe waste a cup of water, so I didn't bother with a diverter.

I was leaning toward PrecisionTemp (propane) before I went with IsoTemp (coolant). Truma (propane) was only available to NAmerican RV manufacturers at the time. I could have ordered one from the UK, but without a warranty. All the RVs we've rented in Europe had Trumas. They are really nice dual air/water heaters. IIRC, Webasto and Espar also make dual heaters (gas, diesel).
 

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Our gravity fill for the fresh water tank is mounted flush on the counter next to the kitchen sink so we can swivel the kitchen faucet over the fill and run the water back into the tank until it runs hot so no water is wasted.

In the shower we run the water into plastic juice pitcher until it reaches the desired temperature and then we can pour that water back into the tank using the gravity fill by the kitchen sink so again no water is wasted adjusting the water temperature.
 

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So ref the Isotemp heat...has anyone built a insulated box inside the van for it? Or an enclosure with a computer fan to exhaust the heat through the floor?
 

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I just got back from the first trip with the Isotemp slim up and running. I was concerned about heat as well since it’s mounted under the bed, and I believe the “slim” is slim due to less insulation. After 5 hours of driving I was surprised at the temperature of the stainless casing, it was only mildly warm to the touch. My ambient temperatures were kind of cool so this wasn’t a definitive test by any means, but some what encouraging. I figure if I have issues I can use the valves I installed to isolate the unit on long drives in warm conditions.


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Hi All,

As I've been floor planning i've realized the isotemp is going to be hard to fit with our current design. The actual dimensions are fairly small (22in x 12in OD) and I was wondering if anyone had mounted it under their van with a shield or something to protect against road debris.

I've read about the thermostat being an issue and I realize I'd have to crawl under the van to reset it (though there is a resettable thermostat?)

Other than that, is this feasible? I don't have my Promaster yet to go out and measure...
What is your battery capacity? How much solar? How long will it take for solar, BB charger to replenish your usage?

Depending, you may wish to skip the alternatives and just use the excess solar/BB to heat your water. Diversion load once your battery bank is full. Simple, and you can save yourself a few hundred $$ and the space.
 

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I just got back from the first trip with the Isotemp slim up and running. I was concerned about heat as well since it’s mounted under the bed, and I believe the “slim” is slim due to less insulation. After 5 hours of driving I was surprised at the temperature of the stainless casing, it was only mildly warm to the touch. My ambient temperatures were kind of cool so this wasn’t a definitive test by any means, but some what encouraging. I figure if I have issues I can use the valves I installed to isolate the unit on long drives in warm conditions.


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I thought the slim was slim due to the rectangular shape. Its not that much slimmer than the cylindrical ones.
 

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So ref the Isotemp heat...has anyone built a insulated box inside the van for it? Or an enclosure with a computer fan to exhaust the heat through the floor?
We have a 4 gallon Spa model under our bed with the water tank, batteries and inverter and don't notice any extra heat coming from the Isotemp. We had a 6 gallon stainless model in a previous camper and never noticed any extra heat either.

I think they are well insulated and along with the thermostatic mixing valve is why we've had hot water for 36 to 48 hours after stopping depending on the size and usage.

The coolant hoses give off a lot of heat so I ran them under the van until they reach the Isotemp and then bring them up into the van as direct as possible. I insulated them with split foam pipe insulation from HD.
 

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I thought the slim was slim due to the rectangular shape. Its not that much slimmer than the cylindrical ones.
The slim, in the 4 gallon size, is available in both the cylinder or square configuration. I have the cylinder, the OD is 11.25”. The square version is about $250 more, must be more involved to manufacture.



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