Water Heater, water lines

[larryburt5@icloud.com]

Next month my 1500 136WB high top is due to start conversion. Classic VW Westfalia layout, with open center, kitchen behind driver, folding seat/bed with utilities and storage underneath.

Hot water has been the most interesting challenge.
Their standard build uses a Precision-Temp propane on-demand heater, located on the passenger side back near the rear doors, right behind the fresh water tank. Seems like a high quality US-made unit, and with the NSP option (No Sidewall Penetration) it vents below the van, making placement easier.
However, the high minimum flow rate (.4 gal/minute) for this heater and all the other on-demand heaters I've looked at means a substantial waste of fresh and gray water space, waiting for the hot water to arrive.
Typical propane tank water heaters all vent out the side, requiring a large opening in the van exterior.
I've found two propane units with small tanks and small venting systems, but neither is currently available and certified for the US. Propex Malaga and Whale Expanse. I'd go for either of these if they were available, so maybe someone knows where to get a US certified model?
With propane out of the picture, I'm left with an electric option. Most of the small tank 120V AC units, like the Bosch 3000T, are designed for home use, not ideal for an RV. The Bosch 3000T and others use a 12 Amp, 1440W element, which would be okay when plugged in, but too much for 12V (120Amps!). Winterizing is also compromised by lack of a drain.
I started looking at marine systems and found IsoTherm makes several small tank models with a 750W element and proper drain valves.
Isotherm 601521 Isotemp Slim Round Electric Water Heater - 4 Gallons
Isotherm 601623 Isotemp Slim Square 4.2 Gal/16L Electric Hot Water Heater
So I'm having one of those installed, probably the slim-square model, likely in the same spot under the bed, rear passenger side.
This will be primarily for plug-in use, though I think I can also pre-heat water while driving through 200Amps of lithium battery and a 2000W inverter.

Water Lines are the next issue.
Pump is a Seaflow, which I believe is 55 PSI. Faucet is a Dometic AC542. GTRV uses 1/2" pex lines for hot and cold water lines to the sink behind the driver and to an outside shower right rear behind the door and adjacent to the water heater.
My calculations show that 1/2 inch lines hold 70% more water (per foot of line) than 3/8, so more wasted cold water waiting for hot to arrive. I've asked them to use 3/8" lines, at least for the hot water lines to the sink and shower. 1/2 inch lines from the fresh tank to the pump and to the water heater. Not sure whether it matters if the cold supply lines to the sink and faucet are 1/2, maybe having 3/8 inch hot and 1/2 inch cold would affect the faucet mixing?

Any thoughts about this setup?

Larry
Portland Oregon

[avanti]

1) Have you considered using a fuel-fired hydronic setup such as an Espar? You can use it both for cabin heating and DHW. With a water-water flash plate heat exchanger, you can have true instant hot water.
2) For long hot water runs, consider installing preheat loop. Just get a little solenoid valve and a push-button timer. Tee in another line from the faucet to somewhere upstream of the water pump. Press the button and the valve opens and circulates hot water to the faucet without wasting a drop.

[GallenH]

Originally Posted by avanti

1) Have you considered using a fuel-fired hydronic setup such as an Espar? You can use it both for cabin heating and DHW. With a water-water flash plate heat exchanger, you can have true instant hot water.
2) For long hot water runs, consider installing preheat loop. Just get a little solenoid valve and a push-button timer. Tee in another line from the faucet to somewhere upstream of the water pump. Press the button and the valve opens and circulates hot water to the faucet without wasting a drop.

I’m assuming that you’re talking about a system where the initial cold water in the hot water line gets put into the fresh water supply and displaces water exiting the hot water tank?

[avanti]

Originally Posted by GallenH

I’m assuming that you’re talking about a system where the initial cold water in the hot water line gets put into the fresh water supply and displaces water exiting the hot water tank?

Yes (if you have a hot water tank; else it comes from the heat exchanger).

Looks like this:

preheat_loop.jpg

Note that you don't have to go all the way back to the tank, just upstream of the pump.

[GeorgeRa]

If you have large fresh water tank ½” lines should be OK. I have Isotemp 15l mounted under the van, plumbed with ½” lines and short runs of 3/8” to the sink faucet, with two sources of heating:

1. 120V 750W
2. Hot coolant from hydronic heater also located under the van. I tend to keep water hot in the Isotemp with electric heater or hydronic heater which gives us instant hot water. Hydronic heater is 5000W so with water hook-up I have no limits with hot water.

For space heating I use Espar Airtronics, located under the passenger seat.

Both unit are control with Eberspacher EasyStart Timer.

[GeorgeRa]

Originally Posted by avanti

Yes (if you have a hot water tank; else it comes from the heat exchanger).

Looks like this:

Attachment 13434

Note that you don't have to go all the way back to the tank, just upstream of the pump.

How do you know when to stop recirculation to prevent hot water going back to fresh water tank? , a temperature senor?

[avanti]

Originally Posted by GeorgeRa

How do you know when to stop recirculation to prevent hot water going back to fresh water tank? , a temperature senor?

I just timed it the first time to see how long it took to get hot. Then I set the timer to that. It was 10 sec in my rig.

I don't think the hot water would ever go back to the fresh tank, no matter how long you ran it. It will just go round and round in the pipe. It could get dangerously hot, maybe. But one or even two button presses is no problem.

This one of the best, easiest, and cheapest mods I have made in our rig.

[ks@yvr]

I have the isotherm slim square heater and frankly never use the electric element. I have it so it can be run on shore power or off the inverter. In almost 2 years the only time I used electric was once at home in the driveway. The tank in my case is heated from the return portion of the dash heater core that goes to the water tank then back to the radiator. We have hot water for at least 2 days when in camp and the hot water is replenished within an hour of running the van engine (probably less but any short drive tends to have the water hot pdq). All our water lines are 1/2 pex and I really don’t think 3/8” would make much difference in preheat of lines to any significant amount of extra water. We have a rear shower and sink plus inside shower curtain and pan also. Plenty of hot water without waiting long for it to get to tye faucet or shower head(s).

[jrobe]

If all I had was an outside shower, I wouldn't spend much time or money on a water heater, even more if it had to be an electric water heater that required shore power or hauling around a generator to even use it. I might even just buy a small portable outside propane water heater since you have to be outside to use the shower anyway.

I have an outdoor shower hookup and an electric heating element on my RV propane water heater and I haven't ever used either one of them. The whole point of my van is to be able to clean up inside in private with warm water without an electric hookup.

[avanti]

Originally Posted by jrobe

I have an outdoor shower hookup and an electric heating element on my RV propane water heater and I haven't ever used either one of them. The whole point of my van is to be able to clean up inside in private with warm water without an electric hookup.

Agree. We also have an outdoor shower, and have literally never used it. I resent it every time I have to winterize it.

Our new van has an indoor shower only.

Might be different if we had a dog who regularly turned up covered in mud, but we don't.

[ks@yvr]

Ah the hot water debate; I for one like a hot shower whether it be outside or inside. I am past the stage of cold showers - call me a whimp if you want but I really like the luxury of a hot shower after a strenuous hike, long bike ride or just at the end of the day. If the sun is up well a ‘cool’ (not cold) shower could be ok but I prefer a ‘hot’ shower. When the sun goes down often the temperature also falls quickly. It’s hot shower time!

We have had the VW Westfalias (3) and we did McGiver a propane heater to the water faucet for showering on our last VW Westfalia, it worked fine but I found it a pain to set up to use for a shower. Our Pleasure Way had both an outside shower and an inside wet bath. We used the outside shower infrequently but often enough that I wanted one in my custom van at the back doors rather than by the drivers door. We do have a dog and although we haven’t had to hose the dog off normally, we have had occasion where the dog has needed a bath due to getting into mud or worse. Since bathing a dog (at least our big dog) ends up being a group bath warm water is preferred - the dog probably couldn’t care less.

In the 2 years we have had our current setup surprisingly we tend to use the rear outside shower more than the inside shower. In the cold we use the inside shower but probably 75% of the time we have used the outside shower.

Where the hot water shines is for washing up the dishes and pots and pans plus for your hands and face between showers. I could live without hot water but I choose not to and we really like that our Isotherm hot water heater always has the water hot through the heat exchanger from the van engine. We are recycling what would be wasted heat. We don’t have to worry about propane or electric but then again the electric element is always there anyway. Generally we don’t just sit in one place for more than a couple of days without moving and as soon as we move and fire up the van engine we start heating the hot water tank again. The hot water stays hot in our Isotherm for about 2 - 3 days, day 3 it is loop warm but still not glacier. The electric water element (750 watt) gets it hot in 20 minutes or if driving for less than an hour does the same.

I am a whimp and I like my hot showers. I think I’ve earned it by now - no more glacier showers if I can help it - been there and got the t-shirt

[GeorgeRa]

We use our outdoor shower very often as a source of hot water for multiple needs. We are not much different than average users of RVs as they are very common on all RVs, it will likely be difficult to find an RV without an outdoor shower or at least a faucet. We had outdoor showers on all RVs except our first 2 Westfalias, I would call it a standard feature on an RV.