We were replacing a hot water heater the other day and the thing had a little check valve on the coldwater line. Homeowner said that it was to prevent warm water from mixing with the cold.
My boss finally convinced him that he didn’t need it. Anyone ever hear of such?
Webby
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Replies
Sounds dangerous to me. It could allow the hot water side to become highly pressurized.
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"{ounds dangerous to me. It could allow the hot water side to become highly pressurized."
What?
Wouldn't the relief valve on the tank prevent dangerous pressurization? I think the OP is talking about some sort of a backflow preventer on the water line feeding the tank.
If the TPV works right it is relatively safe, but who wants the wants it releasing pressure? If there is an expansion tank on the HW side, it's OK, but without one as the water heater heats the cold water it will expand and build up pressure.No one said anthing about a pressure tank being on the water heater.A heat Trap is a different animal from a check valve though.
Edited 3/8/2009 7:23 pm ET by Dam_inspector
Ahh gotcha. Yah no one wants the relief valve going off. Once they go they like to drip a little once they return to normal pressure. At least the ones I have seen.
I assume that if a "heat trap" is installed a expansion tank should be installed on the HW tank's outlet side? Then everything is good to go?
Edited 3/8/2009 7:36 pm by Pebble
Heat traps have a built in pressure relief. Pressure in the tank will vent to the cold water line. A check valve, not so much.
I think that you're right, Pebble. This sounds like a backflow preventer to me, too.
Right, this was on the incoming cold line. I think what the homeowner was saying although I believe incorrectly that it was to prevent the lighter heated water from migrating up the incoming coldwater line.
If this is the case the check valve would be unnecesssary because the cold water doesn't just dump into the water heater it enters the WH at the bottom via the fill tube. Webby
Ever heard of convection?
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
It helps keep the heat in the water heater. There is a kit of two valves one with a ball that floats up and stops heat traveling up the inlet and the opposite for the outlet side. The claim is that you save some heat $.
Someone may come along and expound on if they are worth the expense. I think that they are dielectric connections too.
i always use a spring check valve then an expansion tank on all hwh i install
It was a heat trap to prevent warm water mixing with the cold. Required by code in some areas, and always a good idea.
There should also be a similar one on the hot water line.
(If you've never heard of heat traps should you really be replacing water heaters professionally?)
I am just the helper. Never seen a check valve on a water heater in these parts. That was why I was asking for varied input.
Around here it is basic. incoming cold water to water heater, temp. and presssure protected and piped to a drain then outgoing hot water.
It is unreal though how much homeowners don't even know. My feeling is that the homeowner, or whoever installed it misunderstood how the system works thought a check valve would keep warm water from migrating up the cold line.Webby
What you saw was probably a heat trap fitting, which has a ball inside that floats up to nearly seal off the cold supply when no water is flowing, thereby helping to reduce "thermo-siphoning", a process where the hot (less dense, lighter weight) water rises in the center of a pipe, and cooler water on the outside of the pipe sinks. This process wastes energy--not a lot, but still a waste. The ball does not completely seal off flow, so that heat-expanded water can still get past.
The hot water outlet has a ball that sinks during no-flow times to do the same thing.
You can accomplish the same thing (defeating thermo-siphoning) by simply making a heat trap in both the inlet and outlet pipes of the water heater. This is nothing more than a loop in the flexible connectors that you bend by hand, or, if you're using all rigid pipe, you form the loop with fittings.
As for the points that have been raised about expansion tanks and temperature/pressure relief valves:
Basics: water expands as it heats, and if water heaters have no way of relieving the pressure from expanded water, there is danger even in normal operation. ("Normal", meaning that the thermostat works properly to shut off the energy supply--gas or electric.) The danger is that the expanded water creates pressure that the tank was not designed for, and this can result in pinching or crushing the fire tube on the inside of a gas water heater, thus preventing proper flue action. In both gas and electric tanks, the flexing caused by excess pressure will crack the glass lining that is there to protect the tank from corrosion. Also, the excess pressure will be relieved by T and P relief valve. This might seem OK, but the T and P is not designed to operate as a day-to-day control device, and regular, small spurts and leaks will eventually cause it to seize in the closed position. (Hard water deposits, corrosion are the cause.) When this happens, you have a very dangerous water heater, subject to explosion if the t'stat fails to shut off the energy to the tank.
In an open system, the excess pressure can push back into the main, but most systems are closed by virtue of the check valve on the water meter, and there is no place for the expanded water to go.
You need an expansion tank any time the water heater is in a "closed" system.
Sorry guys I should have been more clear.
We did put in heat traps, my boss convinced the homeowner that his litle check valve would do little to stop the heat loss. He had to show him what we were going to use and explain that they were much better.
Thanks for all the input and opinnion.
Webby