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Old 11-09-2009, 10:27 PM   #11
Senior Member
Join Date: Apr 2007
Location: Reno, NV
Posts: 282
Re: flat plate versus propane hot H2O

My take is I really like my flatplate as long as it's mounted inside (see numerous threads about this). Yes, they now have a drain valve in the flatplate system, but if you forget to drain it when it's freezing ONCE,.... did you destroy it? How about twice? How often do you want to walk out in a 3' snowstorm to get on your knees and drain your flatplate? Then go out again to close it for hot water in the morning, only to go out and drain it again? Really???? This is clearly a solution suggested by people who do not winter camp. Thus, unless it's mounted inside (which SMB won't do for you), I'd worry about it.

One of the pros that several people have mentioned is the space savings of the flatplate. Do not underestimate the value of this! Think about how much people pay for the rear under vehicle storage bin, and how much extra storage that gives you. Applying that same $-per-square ft of storage value, deleting propane is worth a savings of well over $1k.

2006 RB50 6.0 Diesel
Flatplate water heater (mounted INSIDE), portable butane stove (no propane)
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Old 11-10-2009, 09:18 AM   #12
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Join Date: Oct 2009
Posts: 25
Re: flat plate versus propane hot H2O

A 6 gal marine water heater is a flat plate with six gallon storage (won't freeze fast) plus a 1500W electric heater for about $250-300. Reducing water storage by the same volume leaves little space difference. But in the morining, the marine heater is warm and the flat plate is cold.
SMB took the easy way with a flat plate under the vehicle. It requires no design adjustment. But in a more custom design where the water tank is purchased for the vehicle I don't think it's the best choice.
There are cylindrical marine WH that could be put under the vehicle in an insulated box. I believe someone here did a build that way. An electric tank heater could be added to ensure against freeze. Actually preventing all water freezing with electrical heat might be a good way to go for winter camping. Instead of guessing what to set the thermostat at to prevent freezing when not used, just plug the vehicle in.

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Old 01-20-2023, 12:57 PM   #13
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Join Date: May 2018
Location: Arizona
Posts: 373
Originally Posted by warholic View Post
So - pros and cons of propane hot H2O versus flate plate. Any/all comments appreciated.
So I know this is an old thread, but I was investigating how the SMB heat exchangers were utilized. I had previously designed a solar heater system using rooftop PVC along with a heat exchanger and circulation pump to add additional heat content to the "luke warm/hot water supply for the sink and outside shower.

As has been discussed here, you get more hot water out of your system with a circulation pump, but the thought occurred to me to do better than that if you have a hot water tank heater. It doesn't necessarily need to be a water heater but perhaps just an insulated water tank (e.g. 2- gallons).

In the attached figure I'm assuming there is a heater water tank and the idea is that that tank contains pressurized water from the fresh supply. This probably does not do much of anything for a "Tankless" water heater because of the overly limited storage capacity.

So the use case for this is that while you are on your way to your campsite, and have a hot engine. You can flip on the temperature controller which will recirculate the hot water supply through a Normally Closed Solenoid valve till the outlet water hits a predetermined temp.

You could also locate the "T" where the recirculation draws water directly from the sink so you won't be wasting water reheating the water line to the sink/shower. The net result will be that your hot water tank/heater will be full of hot water and the hot water line to the sink/shower will stay hot but you would not waste any water because the water gets recovered by the freshwater supply (from the NC solenoid valve).

Even for a tankless system, the recirculation temperature control is a way to skimp on the water since you will have instant hot water at the point that you "T" off from the hot water supply.

This is still in the concept phase. Since my new build has a Tankless water heater, the heat exchanger may be unnecessary but the recirculation would still offer a nice way to save on fresh water.

One other feature of this system is that by adding a second temperature controller (they are cheap) you could use the circulation system with a tankless system to keep the cold water supply from freezing. Depending upon your system configuration you could sense temperature at the coldest spot and set the temperature accordingly. Just wire the Temp Controller output together in parallel. The low temp circulation would be powered off of House power that is constant ON.
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