Better hot water heater expansion solution?

Old 06-01-16, 08:31 PM
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Better hot water heater expansion solution?

i have seen and read about POPPET type valves and expansion TANKS.

i have been in this house for many years...when i moved in there was no water expansion tank or relief valve (except the usual one on the side of the water heater).

at time of water heater replacement, a WATTS POPPET type relief valve (set at about 95psi) was added.. the normal pressure is set at 65psi.

the poppet started to drip (at all times) a couple years later, had it replaced, now about 2 years later that one drips constantly too.

so questions, before i take the next step-

1. do i need an expansion device?

***NOTE i looked at my neighbor's and a couple other friends' houses, they don't have any expansion relief device either.

2. if yes, is better to have an expansion tank? i am concerned about water standing in contact with rubber diaphragm...(may be not an issue).

3. is there a better relief valve than the usual WATTS brand commonly available online?

Old 06-01-16, 09:05 PM
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I had missed the part that you are referring to a second relief valve rather than the one mounted in the hot water heater.

Set to 65psi it may be very close to system pressure.
After we hear your replies to Paul's questions we can reply further.

Last edited by PJmax; 06-02-16 at 11:08 AM. Reason: misread op
Old 06-02-16, 05:47 AM
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Are you a well system or utility water? Well systems rarely need DHW expansion tanks because the well tank serves the purpose. Utility systems may need an expansion tank depending on whether or not there is a pressure reducing valve (PRV) in the line from the utility.

It doesn't hurt to have an expansion tank even if it's not really required. I wouldn't be concerned about the rubber/water contact. There are millions of well pressure tanks out there and most of them have rubber membranes. Yes, they do eventually wear out, but it will usually last a lot longer than the water heater itself.

I'm not sure why a second relief valve was added unless this is a well system. Well systems usually have a cold water relief valve to protect against rare pump-stuck-on situation where the water pressure can climb really high.

Do you know what the normal water pressure is in your house? An inexpensive pressure gauge that attaches to a hose bib can tell you and will help diagnose your problem.
Old 06-02-16, 11:29 PM
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pj max and carbide tipped....

1. i have city water (not well)

2. the inlet to the house is thru a pressure reducer set at 65psi...i.e., the normal system is about 65 psi.

3. a while back i added a pressure gauge with a T so i can always see the pressure without having to hook up a temp gauge

4. the POPPET relief valve was set at about 95 psi and would drip a bit after the the hot water heater had been firing for some time...the pressure (as expected) would slowly rise from 65 till the POPPET started to drip and the system pressure would stay at 95 till any of the tap is opened..

5. the recommendation to add an expansion tank (or a relief device), as i recall was in the installation manual of the water heater to cap the pressure rise due expansion...and the poppet did did its job very well...except it started to wast water by dripping even at the normal 65 steady state pressure.

6. appreciate the note on use of expansion tanks...i.e., millions of well-water systems use it and i should not be concerned.
Old 06-03-16, 12:31 AM
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Having a pressure reducing valve on the incoming water makes your house a "closed system" because the water cannot "back up" to the city main in case of pressure rise downstream (house side) of the pressure reducing valve. Installing a separate pressure relief (safety) valve with a set pressure a bit higher than the nominal setting of the pressure reducing valve used to be common to prevent excessive pressure rise due to heating a full tank of water from cold.

The problem with using a safety valve is that it will likely lift slightly and discharge a few dribbles of water each time there is a significant input of cold water to the heater, meaning every time that a significant amount of hot water is used. This could happen several times a day in a large household. Eventually the seating surfaces (seat and disc) of the safety valve will erode to the point that the valve will leak constantly. At that point the valve needs to be replaced.

By substituting a properly sized and pressurized expansion tank for the safety valve you eliminate the periodic discharge of water and the wearing of the valve. The ONLY reason for the safety valve is that it is less expensive than the expansion tank. Expansion tanks are sized according to the volume of the water heater tank and the maximum temperature differential from the incoming water and the outgoing water. Too small an expansion tank will still allow an excessive rise in pressure whereas a larger-than-necessary expansion tank merely has a higher capital cost and possible problems in the mounting of the tank.

The air side of the expansion tank needs to be pressurized to the same nominal pressure from the pressure reducing valve or just a fraction higher. The air pressure on an installed expansion tank can only be measured when the water side pressure is zero. The air pressure should be checked every year or two.

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