Water Heater Expansion Tank Pressure

AnthVale

My water heater was 16 years old and knocking/banging a lot. I assumed there was a buildup of sediment, considering the water is very hard where I live.

I bought and installed in a new water heater and there's still some slight knocking. I don't believe there's a water feed regular or check valve anywhere but the issue is the entire main feed is in a crawlspace that's a mess right now and it's completely covered with insulation. Tough to tell but there could be a check or prv somewhere in there.

Either way, I want to add an expansion tank just because.

The water heater manufacturer wants me to set it at 10-15PSI higher than the incoming water pressure. I pushed back, saying I thought it was supposed to be equal to the incoming pressure…

What are everyone's thoughts here? My incoming pressure is 70 PSI. I planned to set the tank to 70 psi.

The Rheem technician also mentioned that they recommend the pressure be no higher than 40 PSI inside the water heater. And I said, "Well, that would be very low water pressure at the faucets wouldn't it?"….She wasn't sure how to respond and then mentioned that alternatively, they recommend having an Xtank instead to alleviate some pressure.

So, I'm hoping adding this Xtank will eliminate the knocking entirely.

Thanks in advance.

leonz

It sounds as if you are dealing with water hammer. is there a water pressure regulator after the water meter? You should reduce the incoming system pressure. Reducing the incoming water pressure will reduce the water hammer. My water pressure is set at 20/40 PSIG at my well tank and I have plenty of water flow with no water hammer.

Jamie Hall

70psig is legal — but pretty high for plumbing. 40 to 60 is better. However, if you are not certain there is a pressure reducing valve or check valve on the system, of if you know there is, an expansion tank on the hot water is required. I'd set it about at the lowest incoming pressure you see, but there is no harm to setting it a few pounds higher.

I doubt that it will do anything for the knocking — water hammer. But reducing the incoming pressure might.

hot_rod

maximum pressure on most faucets and toilet valves is 80 psi

Typical PRVs are factory set at 45 or 50 psi

If that is sufficient pressure, no need to fun 70

Often times removing the flow restriction in the shower heads allows you to run lower pressure and get a good flow.

Set the expansion tank to match the regulator pressure, according to the tank instructions

Water hammer starts when a valve closes quickly, wash machines , dishwashers, lawn sprinklers. The expansion tank should help, or add water hammer arestors st the machines

SuperTech

I always measure the water pressure and set the tank pressure to match. 70 is a little high but not uncommon. If you have a reducing valve I would lower the pressure to 60. Try to flush the new tank annually to avoid sediment buildup and kettling. Inspect the sacrificial anode rod every 2-3 years and replace it if becomes 1/3 depleted. A powered anode is usually an upgrade from a sacrificial anode rod.

AnthVale

Thank you everyone. @SuperTech I have to go into the crawlspace and check for a prv. I do not believe there is one so I think I will leave it at 70PSI if you think that's ok. I've been fixing the plumbing for a month now and I just need to get the heat on (I'm in New Hampshire, it's 50 every morning in my house).

Perhaps I can revisit next spring/summer and put a PRV somewhere to take it from 70 to 50-60psi?

As far as the location for the new PRV (if there isn't one already), would I want it just where it enters the crawlspace from the street or where it enters the house? My meter is right when it enters up into the house from the crawlspace.

@hot_rod It's not making noise when valves close quickly (although this was a problem with old water heater when I turned faucets off..weirdly it's stopped with new heater), it's making noise sorta… randomly periodically. It's a very faint knocking. With my old water heater it was much louder and more often. Now, it's much softer and way less agressive.

I do not have the time or energy to add another PRV at the moment. Is it safe to run this water tank for the time being at 70psi with my expansion tank set to 70psi? Everything I google is saying 50-70PSI is ideal for home water pressure.

EDIT: Went down in the crawlspace and I found what looks like a potential PRV. It also seems very old and it was a bit moist on the part on the right side. It does get moist in the crawlspace (i know, totally other horrible issue i'm dealing with), so I'm not sure if it's that or if this is leaking. There is no valve before it so I'm guessing it would require the town to shut off the water to replace this.

Looks like i will wait till next year maybe.

Thanks,

Larry Weingarten

Hi @AnthVale , You've been given some good advice above.👍️ The photo you share is of a gate or maybe globe valve, not a regulator. A test you can perform is to put a pressure gauge on the water heater drain valve and then fire up the heater. Do not use any water during this test. As the water heats, it expands, so if you see the pressure rising you know something is preventing the expanding water from flowing backwards into the supply line. If pressure doesn't rise, it suggests there is no regulator.

Also, code requires regulators if pressure is at 80 or higher. If you buy a gauge to test pressure, get one with the added red pointer. It will tell you what the maximum pressure has been. Leave it on for 24 hours and see if it ever goes uo to 80 psi. If so, a reducer makes sense.

Yours, Larry

SuperTech

I'm not familiar with what you have in the picture. Doesn't look like any PRV that I have seen. I have measured 70 PSI before and set the precharge to 70 PSI without any problems. From what I have learned that is on the high end of what is acceptable.

AnthVale

@Larry Weingarten Fantastic! Could this valve go anywhere on the main feed or does it need to be on the water heater drain valve? I only ask cause I have plans to add a gauge to the main feed.

Thank you.

AnthVale

@SuperTech thank you.

Also, there is the letter K on the side of the valve. I think Larry may be right saying it's a Globe valve. Don't these just reduce water pressure too?

Thanks,

Larry Weingarten

Hi, You want the regulator on the main feed line, so everything in the house is protected. Also, if a regulator is installed, you'll want an expansion tank in the cold line, somewhere downstream of the regulator. Allison Bailes at Energy Vanguard is replumbing his house now, and has this very setup with gauges and regulator pictured. Might be worth looking him up. Globe valves can be used as shutoffs and for throttling flow. They simply act as a flow restrictor and won't regulate pressure.

Yours, Larry

AnthVale

Thanks Larry. I ment the gauge. Not the PRV.

Cheers, @Larry Weingarten

Larry Weingarten

Hi, Here's Allison's post. https://www.energyvanguard.com/blog/a-plumbing-feature-every-home-should-have/

Yours, Larry

AnthVale

Thanks, Larry. I actually have a similar setup for my closed loop heating system with gauges on either side of the prv. But, there is no PRV on my domestic hot water or any of the main feed coming in so I was just going to ignore it for now and let it operate at 70psi. Perhaps next spring I can remove that globe valve and replace it with a PRV???

For now I'm going to monitor the incoming pressure and keep the expansion tank for the water heater at that same pressure.

Perhaps, next spring I could put a pressure reducing valve in place and set the PSI to something like 60 and add some valves/gauges perhaps.

Thank you

Larry Weingarten

Hi, I'm a fan of keeping things simple, so there is less to fail. As long as 70 psi isn't hurting things, and as long as you have verified that pressure doesn't go higher, I'd skip the regulator. Is there anything in the supply to prevent water from traveling back to the main? If not, you don't need an expansion tank. 🤔

Yours, Larry

AnthVale

Unfortunately, there's about 30 ft of heavily insulated main feed pipe in the crawl space before it gets to my mechanical room and I am not entirely sure if there is a check valve hiding somewhere in there. The globe valve I found I was very lucky and it was right inside the bulkhead door. It was also heavily insulated and I just noticed a different shape so I peeled back the insulation.

If I had to guess there is probably no check valve. As that's what the town states in their documentations outside of a few scenarios like sprinkler systems etc.

I already plumbed in the expansion tank. Everything I've read mentions it will at least relieve some stress on the water heater if there is any increase in pressure.

Oh well. It's going in! And it's going in at 70psi so I can move on haha!

Thank you

AnthVale

Update. I put a pressure gauge on where the expansion tank is supposed to be going and it's reading 62 PSI. I'm wondering if my other gauge, which is on half inch pipe after my PRV for my heating system, is higher in pressure because of the pipe size? It was also in a very small area maybe about 6 in of pipe before another valve was shut off.

This new gauge is about 1 ft away from the water heater on 3/4-in pipe.

Anyways, why do I have this slight knocking with 62psi. I'm gonna see if it goes away with the xtank

Larry Weingarten

Hi, Can you describe the knocking in more detail… when it happens… tank heating or not… concurrant water usage 😉

Yours, Larry

hot_rod

The issue can be the water pressure supplied to your house may spike or increase. Could be the water supplier has a faulty main line regulator. Or the level in their elevated tanks changes your pressure. Some cities have fire pump that can spike main line pressure when they exercise them.

A PRV is a wise investment to protect your entire system. Possibly save water also.

I think current plumbing codes suggest 20 psi minimum, 80 psi max.

Get one of these and connect it to a hose bib for a week, see where the pressure peaks.

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