Expansion tank requirements

nytech28

hay techs got a random call ,with expansion tank with no air , it's installed on a 73 gallon domestic hot water tank, the 73 gallon tank is serving 2nd flr apartment & installed in the same apartment , tananet also saying his water pressure is high at his faucets & thinks it should be lower , know my questions is, 73 gallon tank for single apt is it over kill ? does he really need expansion tank on the DHW-tank ? does he need some type of pressure reducing valve on his cold water feed to his apt ? , i haven't seen the job yet , but any good info would help 

Intplm.

First, find out why he thinks the pressure is too high. What making him think that?

Bring a pressure test gauge (see below) with you and check the number. There is plenty of debate on what the usable pressures should be. Some code books will not even give a number. Premature mechanical issues can arise from high pressures. If a PRV is needed I like to set them up at sixty-five psi. But is a PRV really needed? Is there one currently installed?

As for the expansion tank. You usually only need one if you have a "closed system". A system becomes closed when some type of check valve is installed near or at the water main. The tank will absorb shock when a check moves when the system is activated. It will also absorb thermal expansion. Meaning, when water is heated the pressure rises.

If there are no checks of any sort, this would be called an open system. The water main/water supply is uninterrupted by a check, of back-flow-preventer (PRV) or Vacuum breaker (VB) and should not create any issues.

A common thing I like about having a expansion tank on a water heater is that it absorbs the shock and does not allow my relief valve to leak or spit water or ware it out to soon.

Intplm.

Oh, and one other thing. Yes. The size of that 73 Gallon ?? Tank is over kill.

nytech28

I would have to check the pressure for accurate information, & see if prv are inatalled

nytech28

yes I figured i 40 gallons would be just fine

Intplm.

https://forum.heatinghelp.com/discussion/comment/1848467#Comment_1848467

Great. Hope you will come back here when you get a look and share what you find.

nytech28

yes i.ll update thanks for responding

hot_rod

I think all the plumbing codes list 80 psi max. Which is faucets and plumbing fixtures sometimes show in the spec.

Codes used to show 15 psi minimum, maybe still do?

EBEBRATT-Ed

40-50 lbs is more than enough

nytech28

i am scheduled for tomorrow i.ll check & update you , also I am looking to add air to the expansion tank that's on the DHW-tank seems like no air , do u recommend adding same air as bldg pressure ? also can I add air to ex-tank while it's installed on pipe ?

hot_rod

you will need to shut the water off, drop the pressure, then check and adjust the air in the tank

First push in the air stem, if water comes out, the diaphragm is ruptured

You also need to know the water pressure, run a faucet for a few seconds then check, in case there is some thermal expansion

Most prv are set between 45-50 from the factory, that should be plenty

73 gallon is an odd size, 75 for gas, 80 for electric typically

nytech28

ok will check it out ,tnx

nytech28

update i visited the job today , the pressure @ the hot water tank was 65psi , i added about the same air to the expention tank , i don't see any PRV on the pipes thats visible to me , owner wants to replace the DHW-tank with smaller size preferly wall hung units to save space in the closet , in near future. there is no issues so far ,so I toke pictures & material if he wants to further do work in near future .

pecmsg

when you pressurized the X-tank was the water pressure zero?

What’s with all the rust on the exhaust piping?

hot_rod

This is a handy gauge to have, it will capture pressure spikes.

If the home is on a public system, most often there is a backflow device somewhere. It could be built into the water meter yoke out in a pit in the yard?

This red hand in the gauge will capture that thermal expansion increase pressure.

Intplm.

https://forum.heatinghelp.com/discussion/comment/1848592#Comment_1848592

@pecmsg That rust looking stuff? Maybe high temp caulk or duct seal? Thats what it looks like to me.

nytech28

the red stuff on exaust pipe is hightemp sealent done slopy , i checked the pressure with gauge with city water line open to water tank & reading @ 65psi & i mentioned before i added air to ex-tank to tank pressure, want to know if I really need to add ?? Pressure reducing valve cause the tanent saying the pressure is to high for him , i would have to redue some of the piping to fit the PRV ,the horizontal pipe with ball valve in middle of pipes in picture is the cold water feed coming to apt. also any recommendation on a tankless water heater that's good for single apt ?

Kaos

Looks like there are check vavles on the cold water feed. With the expansion tank improperly charged and such a big water heater, the pressure would skyrocket each time the tank cycles. I'm pretty sure that was the issue.

Assuming the expansion tank works and now properly charged, the high pressure issue should go away.

nytech28

yes exactly like you mentioned , the tananet wants to save space & reduce tank size , he wants a tankless water heater to be hung on wall , any recommendations?? & i truly aprecaite everyone helping out with there suggestions.

Intplm.

https://forum.heatinghelp.com/discussion/comment/1848626#Comment_1848626

I would not reduce the pressure if you really don't have to.. Ask the tenant from what fixture is the water pressure too high? Is it the shower that is the complaint? You can fix that by changing the shower head.

Most always a tenant will complain about the pressure being to low, not to high. That being said, if the tenant cannot turn the water on half way at a isolated fixture or the pressure is to high everywhere go ahead and add a PRV.

nytech28

i would have to get in touch with him after adjusting air to ex.tank if water pressure feels less , while I was there it seemed it was all house on cold & hot water lines.

hot_rod

the expansion tank may be a bit small for that size water heater. What temperature does it run?

With the two check valves I suspect the pressure increases as the tank warms. That is why you add a gauge with the recording hand as shown a couple posts up.

The incoming pressure may be steady at 65 psi. As the water heats in the tank, the pressure downstream of those checks will increase, as it cannot push back into the main line.

nytech28

the hot water temp felt around 140° plus , seemed hoter then that, I acually lower its set.pt on the DHW-tank gas valve , & yes the EX-tank seems to be smaller , it's 5gallon probably 9-10 gallon would be fine, but tananet wants to repalce it soon with 40gallon.

hot_rod

just be careful with a tank set that high, especially a rental!

There is usually a label on the tank warning of temperature in excess of 125F. At the very least the shower valve should be limited.

Check with the local inspectors for their interpretation of the code regarding DHW supply temperatures