Add recirc to tankless water heater

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PancakeBill

PancakeBill

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Apr 9, 2005
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ecently replaced my aging Atwood water heater with a tankless water heater. There is a delay in getting hot water, and the cold will either be collected to use for something or gp into the gray tank. I want to add a recirculation system to save the waste. I have seen some that just put the water back into the fresh tank, and I guess this is OK, but don't really want to warm that water up. Another option would be to use solenoid to insert back into the feed, but it seems this might hasten the heating, what happens when you turn off solenoid and cold from tank is fed in?
Has anyone come up with a method? If putting water back into tank, from vent line or from drain line, or new port into tank?
 
While that will fix one issue, of many with tankless water heaters (and I wish I could add that to my 2022 Class A) I still would prefer the system I have here in this Y2K RV. A simple six-gallon tank with a Hot Rod. Works perfectly and wastes nothing, not even using any propane and I have hot water in a few seconds with no temp changes.

-Don- Tucson, AZ
 
Adding recirculation to a tankless heater amounts to having a tanked heater - the plumbing becomes the tank. For a limited capacity system like a camper there's only so many places for this water to go. How it's plumbed might reduce the cycling but it would be a pretty intricate/complex system to mitigate it. All to mimic the operation of a tanked heater. Tankless brings limitless hot water as a feature but I think a bit misapplied in a system with a ~50 gallon supply.

Mark B.
Albuquerque, NM
 
The 240VAC/6,000 Watt electric/propane tankless water heater prototype we are currently testing has recirculation built into it. In other words, it only allows water to flow once it has reached the setpoint temp. We also only use a short length of 1/4" diameter Type A PEX to move our hot water which results in the wasted water being less than 4 ounces at our furthest shower head location. We modified our kitchen to use an induction/propane cooktop arrangement too. We like not having to use any propane when we have 50A shore power and being able to do long-duration dry camp camping when we don't. And we only need a 100AH LiFePO4 battery, 200 Watt portable solar panel suitcase and 3,000 Watt Inverter to accomplish this in a 17 foot, 3,500 pound max weight fiberglass trailer.
 

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It doesn't take long for warm, and 30 secs for max, but I only have a 30 gal fresh tank. I remeved a failing 6 gal water heater. If we were in a FHU CG no biggie. but boondockng, don't want to waste. My concern was plumbing it back to the water tank and increasing the temp of the tank, but I think now it is a non-issue.

I found one setup that uses a temp sense switch, so turn on water, it starts flowing, temp switch activates solenoid, and sends cold back to tank, as it reaches set temp it turns solenoid off sending water to faucet. Minimal plumbing. Would work for both shower and kitchen.
 
Recirculating the water in a tankless means the flame will go on and off even when not using water. You would also have to have the recirc line connected to the furthest hot water line.
 
DonTom said:
Not an issue in RVs AFAIK. There is an on/off switch for the tankless. Simply turn it off when not in use.

-Don- Tucson, AZ
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Precisely... A properly designed tankless water heater doesn't use any significant electrical power or any propane at all until there is a call for hot water. So no need to even turn it OFF. The tankless water heater that we are currently testing only initiates the recirc process internally before releasing water at the exact setpoint temp. Thus far, we have found this tankless water heater to be game changing for dry camping water savings when using propane and for taking long showers when hooked to 50A 240VAC with continuous dump out capability. We only have a 25 gallon potable water tank and 32 gallon gray water tank. Under a NDA so unfortunately can't say any more at this time.
 
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When I built my cargo conversion, I installed a tankless water heater. After a couple of trips I took it out and installed a conventional 6g propane/electric water heater. The tankless would only work if the hot water was turned on almost all the way. We like to take showers, and wash dishes, at reduced flow. The tankless would not cooperate with this. I like having the option to use shore power or propane to get hot water.
 
SuwanneeDave said:
When I built my cargo conversion, I installed a tankless water heater. After a couple of trips I took it out and installed a conventional 6g propane/electric water heater. The tankless would only work if the hot water was turned on almost all the way. We like to take showers, and wash dishes, at reduced flow. The tankless would not cooperate with this. I like having the option to use shore power or propane to get hot water.
Click to expand...
True. All the RV tankless water heaters currently available in US are poorly designed, poorly manufactured and don't meet RV requirements. And I fully agree, if a RV tankless water heater doesn't operate perfectly for RV needs using both propane and 240VAC electric, it is totally worthless RV water heater.
 
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SuwanneeDave said:
The tankless would only work if the hot water was turned on almost all the way.
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Often all the way or even past that (meaning it will not work at all). Needs to have the flow to turn on and sometimes cannot get that much flow at an RV park, or the RV water pump. Everything has to be perfect for them to even work poorly! But if you turn the shower on to waste even more water, then you will most likely get your hot water at the sinks.

I wonder whose stupid idea it was to start using tankless water heaters in RVs. Whoever it was, needs to be forced to use one for the rest of his life!

-Don- Tucson, AZ
 
I have one in my sticks and brick. Minimum water flow for the burner to come on is 1/2 to 3/4 GPM.This is so the coil doesn't over heat and burst. Max, depending on the burner BTU, is about 10 GPM. Ours is a single use at about 4 GPM. DON"T run the dishwasher is someone is taking a shower.
 
gwinger said:
I have one in my sticks and brick. Minimum water flow for the burner to come on is 1/2 to 3/4 GPM.This is so the coil doesn't over heat and burst. Max, depending on the burner BTU, is about 10 GPM. Ours is a single use at about 4 GPM. DON"T run the dishwasher is someone is taking a shower.
Click to expand...
I had a Takagi Tankless water heater installed in my old house in South San Francisco. It worked perfectly in every way possible—better than tanked! Perhaps because it was located right behind the bathroom and computerized to keep the temperature exactly where set.

If they could only get them to work like that in RVs.

-Don- Tucson, AZ
 
SuwanneeDave said:
After a couple of trips I took it out and installed a conventional 6g propane/electric water heater.
Click to expand...
I have been thinking about doing that in my 2022 Class A. It would be great if it worked as well as the tanked in this Y2K Class C, which is a simple six-gallon with a Hot Rod heater:
1731168502031.png

How much trouble was it to change over from tankless to tanked? What brands did you change from and to?

It shouldn't be too difficult in my Class A because it can be tanked or tankless when new. But I didn't have that choice besides, I didn't then know the tankless worked so poorly in RVs at that time.

-Don- Tucson, AZ
 
Tankless hot water heaters have to be sized properly to be effective and location is an important consideration in the calculation. Since you will probably be using the rv in different parts of the country results will be less consistent than in a house.

Every manufacturer sells units with different flow rates and btu settings to account for this. You really have to know what you are doing to install one in an rv to get good performance.

www.thinktankhome.com

What Size Tankless Water Heater Do I Need? (With Calculator) - Think Tank Home

Use this sizing calculator to determine what size tankless water heater you need. Plus other helpful buying advice.
www.thinktankhome.com www.thinktankhome.com
 
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