Connecting outside hot water source to low point hot water drain

[Jacovite]

I have a Forrest river Puma that has both a cold water and hot water low point drains. I would like to connect to a tankless hot water tank which is in the building close to the RV. there is a cutoff valve for the hot water at the RV hot water tank. My question is wether or not I can run hot water into the low point drain (would put a pressure regulator in line as well.

 

[Rene T]

Welcome to the forum.
I don't see any reason for that not working. Good luck and let us know how you make out.

 

[Henry J Fate]

In theory it will work but without a piping diagram, it would be difficult to be certain.

Your best approach would be to be sure that the tankless hot water feed flows into the onboard hot water tank which essentially would replace the cold water feed into the onboard tank. The connection to the onboard tank should be made between the tank and the cold water IN check valve. The check valve (which should be in the cold water make up to the onboard tank) prevents hot water from migrating from the onboard tank backwards and into the cold water lines that feed your sinks and showers. This occurs primarily due to thermal expansion of the water being heated.

This plumbing will basically place your tankless heater in parallel with the onboard tank and allows you to heat the water with either or both.

This would also require an additional check valve to be placed between the tankless heater and the onboard tank to prevent water flowing from the onboard system to the instant hot water system and beyond.

 

[Phil-T]

Sounds reasonable.  Some units have a hot water bypass valve, (used for when winterizing/draining the hot water heater).  If you have the bypass valve, you could easily use the outside hot water source. My hotwater system has that bypass valve.

 

[John From Detroit]

There are two or 3 different how water systems in RV/s when it comes to the valving

1 Valve
2 Valve
3 Valve

If you have a 3 valve system they are HOT COLD and Bypass and work the way you want.
Close all 3 and drain the water heater tank if it's an Atwood pull one of the wires off the ECO and it's protected against accidental turn on  (Wow that was easy)

In the 2 valve system still pull that wire. but set one valve to use (Cold) and the other (Hot) to bypass that should do it.

In the one valve system.. There is a check valve on the hot water outlet so in THEORY but. no matter which way you set the bypass vavle water flows either to the water heater or to the bypass line and into the hot lines. I'm not sure how you can prevent it.

IN all three cases (this might work)

The connections to the water heater are 1/2 inch IPT threaded connectors.. A couple brass plugs from ye old hardware and you simply disonnect the thing, plug the lines. pull the wire if it's an atwood  (Can not tell you how to protect a surburan as I don't have one) and done.

 

[Rene T]

A suburban usually has a switch in the lower left hand corner of the heater behind the access door and it may have a dedicated circuit breaker.

 

[mel s]

In theory it will work but without a piping diagram, it would be difficult to be certain.
Your best approach would be to be sure that the tankless hot water feed flows into the onboard hot water tank which essentially would replace the cold water feed into the onboard tank. The connection to the onboard tank should be made between the tank and the cold water IN check valve. The check valve (which should be in the cold water make up to the onboard tank) prevents hot water from migrating from the onboard tank backwards and into the cold water lines that feed your sinks and showers. This occurs primarily due to thermal expansion of the water being heated.
This plumbing will basically place your tankless heater in parallel with the onboard tank and allows you to heat the water with either or both.
This would also require an additional check valve to be placed between the tankless heater and the onboard tank to prevent water flowing from the onboard system to the instant hot water system and beyond.

Henry J Fate
Logic and common sense dictate that the OUTPUT, FROM the external tank less water heater, should go INTO the existing RV hot waterline at the OUTPUT of the RV water heater tank....

(If "between the tank and the cold water IN check valve" you will have to run all of the unheated water in the the RV water heater tank OUT before hot water can reach any hot water faucet).

 

[Henry J Fate]

You are correct Mel but there would have to be an assumption that the instant hot water feed would be adequate to supply enough hot water for all intended usage with a good steady temperature and flow rate especially for showers. Since we don't  know what the instant hot water system is or the capacity and the fact it is located in a different building.... using it as the cold water make up for the existing tank would eliminate all of those issues.

My piping suggestion was based on the most likely scenario which probably finds that the tankless hot water feed would not be suitable for all usage. Yes, the onboard tank will need to be heated sparingly but the onboard tank could hand off duty to the instant for the remainder of the usage and provide stable temperature.

It may work as you suggest but unless the math is done, who knows. I guess hook it up and try it. It may be fine for what he needs and apparently totally free but the sure way is to use it as a feed to the main system.

One other issue with this sort of modification is volume. Volume becomes dependant on the instant hot water feed. If the instant does not provide enough volume for the usage then it becomes necessary to mix in an additional source (probably cold water in this case) before the instant makes up the tank water or in your suggestion, the main hot water feed. This would increase volume which would be mostly an issue for showers.

 

[grashley]

As I read the OP, the instant HW was in the building with the RV AND near the RV.  Whatever...

The biggest danger here is if the hot water got into the cold water lines and scalded an unsuspecting user.

My approach would be to plumb the HW to the RV heater DRAIN PLUG with appropriate fittings.  Hopefully, it has a 3 valve bypass setup, and you can close the incoming cold water valve and bypass valve.  This would not allow hot water into the cold piping.

Let us know what you do.

 

[CharlesinGA]

A hose capable of hot water will also be needed, not your usual garden hose.

Charles