setting up pump and hot water heater

[decodancer]

Right now I have a 20 gallon water tank hooked up to a pump which goes right to my 2 1/2 gallon on demand hot water heater. I have a spray hose from the heater to my bathtub/sink. The pump is run to my van battery and I can get cold water even without hookups.
My problem is that when I am plugged in and turn my hot water heater on, I cannot regulate the temperature. I have to remember to turn the heater off after five minutes or the water is scalding. Then I have to run it until it cools off which wastes water and also gets too cold to be comfortable very quickly.
I'd like to use pvc pipe with a shutoff valve to be able to add cold water to the water from my hot water tank. I have done this (on my dog grooming van) before but just can't remember how. Here is a picture of my current setup.

 

[GRC]

Are you saying you have a 2.5gal, 110v hot water tank you are using when plugged into shore power? Tee into the pump discharge line that feeds cold water to your tank and run a new line bypassing your hot water tank to the cold water side of a new shower valve. Run your hot water tank discharge line to the hot water side of the shower valve. If I understand your situation that will allow you to adjust your water temperature.

You might watch video of PEX water lines and fittings on youtube. You can get that at Lowes and Home Depot. Pretty quick and simple.

 

[highdesertranger]

ok not really sure about what you have. on demand hot water heaters are not rated at just 2 1/2 gallons. they would be rated at 2 1/2 gallons per minute. do you have a pic of your heater. on an rv on demand system you do have a little control of the temp with the flow rate. the higher the flow the cooler the water(less time in the heater to get hot). if you have a residential on demand water heater with an rv pump supplying the water your flow is way short of what should be. you could put a blend valve in but you really shouldn't run a residential on demand water heater off a rv pump. we need more info maybe some pics of what we are dealing with here. highdesertranger

 

[SoulRaven]

First I'd make sure there isn't a temperature adjustment hiding under the cover.

Since I understand your case is a little unusual, I would add a T in the line both before and after the water heater. Switch to run the cold water straight through, with an added faucet in line, and run the water heater off the new T'd line.

After the water heater, also put an inline faucet in the hot line so you can regulate both hot & cold, and and thus flow rate separately.

Good Luck

 

[Reducto]

Looks like a point of use water heater, not an on-demand water heater. They're made to put under bathroom sinks and such so you get instant hot water instead of having to wait for it to get there from the other end of the house.

Here is how I would set it up:
Put a T in the line after the pump. One end goes to the water heater, the other goes directly to the cold inlet on your faucet. The line coming out of the heater goes to the hot inlet on your faucet

Obviously you'll need a faucet with hot and cold inlets if you don't have one already. You don't need a shutoff valve - it now just works like a basic household system. If you prefer to just have the sprayer you could probably use a bathtub control to mix the temperature.

Offgrid is right though - you may have an adjustment in there somewhere which might get you down to 100 degrees.

 

[Zil]

There are tempering valves that auto mix cold water into the hot water for use on hot water from your home heating system. Plumbing supply store.

 

[decodancer]

Thanks everyone. You are right Reducto, It is a point of use water heater. It does run on 110 which is fine since I will usually have hookups. I do need the spray hose as I do dog grooming as a way to make extra cash. I think I understand what I need to do. T off after the pump and then a T again after the hot water heater. If I put a valve at the second T, I can control the cold water. There is an adjustment on the heater but I want to be able to set it as hot as possible and regulate with cold water so that I have warm water for a longer time. Both for dog grooming and my own use, ice water in winter is no fun.

 

[Donedirtcheap]

The temperature should be adjusted at the faucet. The water pump should be plumbed to the water heater and the cold side of the faucet. Its a balancing act between the two faucet handles, just like in your house. Overall I would use a bath shower fixture. Go from the tank to the pump, then have two lines off the pump, one to the water heater and one to the cold side of the shower fixture, then from the water heater to the hot side of the shower fixture. Yes you can try to adjust the temperature of the water heater but the safe way to do it is just like in a house and that is through a shower fixture because they have SCALD GUARDS built in. If the water heater malfunctions, young or old people fumble with the fixture, no one is scalded.
Not yelling at you with those words, just want you to know how important it is. It goes without saying that you dont want an accident with an animal or get sued or bit when the dog flips out.
The scald guard is probably now code is all areas now.

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Thats also the reason you dont bath in your kitchen sink or laundry sink. People usually want very hot water for good dishwasher operation and other things so water heaters put out very hot water. The scald guard is an excellent device in a bath tub/ shower. I know you are not running a dish washer but you still absoluetly want the safety feature. The other reason you actually WANT very hot water is because you are using a small water heater. If you start out with a water heater full of say 100 degree water you will only have that much water for the dog. If you start out with 130 degree water you will be blending cold water with it and ending up with maybe 15 to 20 gallons of 100 degree water. The hotter the starting temp the less likely it will be that you run out of the DESIRED temp water that you want. The hotter the water the longer and more consistant you delivery temperature will be.
This is an area that you want to do correctly and not be fooling around.