Hot water heater question - anybody have a thought or two?

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PopPopT

PopPopT

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Deer Lodge, Tennessee
Maybe not a question for every homestead but I'll be most have a hot water heater. Ours happens to be a standard electric hot water heater, sits in a closet, the water heater is about 20" around and about 5' tall. (It came with the house when we bought it and hasn't caused us any problems.)

I have been noticing that pressure seems to build in the water lines when no one uses the water for a while. I don't particularly like that. And I was wondering about what might be causing it. I know of a couple of things it could be...

The reason the water heater came to mind was because of living in an RV for a decade. That little 5 gallon hot water heater was built in such a way that there was a bubble of air in the top of it. It was supposed to be that way. Over time, that bubble of air would dissolve and go away and when it did, the water would do something very much like what I am seeing at home. Pressure would build when no one ran the water for a while.

So I got to wondering whether a home hot water heater is kinda the same? Does it need that bubble of water to act as a "pressure tank" of sorts? It's been over a year since I drained it, so I really should do that anyway. But I wondered about the air bubble thing.

Mr. Google was no help at all and kept trying to tell me about air bubbles in the water that was coming out of the tap. Related subject, but that wasn't what I was asking about. (sigh) Sometimes he can be quite dense. Anyway...

Anybody know? I just get curious about such things.

:)

Thanks!
 
havasu said:
How have you confirmed pressure is building in you W/H? Is it blowing out you TPR? Have you considered adding an expansion tank?
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Pressure at the tap. Easy to see and hear. It doesn't take long with water running to bleed off the higher pressure.

The relief valve is plumbed to drain under the house. I have seen it drip a little when down under there but it's been a while since I looked.

I'm thinking an expansion tank may indeed be a good thing to look into. Wouldn't be difficult to install. I actually did that in our RV because I got tired of putting air back into the hot water tank to basically do the same job. I have just never heard whether the hot water heater has such a thing pretty much built in by design. But inquiring minds... :)
 
PopPopT said:
Pressure at the tap. Easy to see and hear. It doesn't take long with water running to bleed off the higher pressure.

The relief valve is plumbed to drain under the house. I have seen it drip a little when down under there but it's been a while since I looked.

I'm thinking an expansion tank may indeed be a good thing to look into. Wouldn't be difficult to install. I actually did that in our RV because I got tired of putting air back into the hot water tank to basically do the same job. I have just never heard whether the household hot water heater has such a thing pretty much built in by design. But inquiring minds... :)
Click to expand...
 
I know in my area, they increase water pressure in the morning to compensate for all the morning flushes. It is imperative you have a pressure reducing valve if you are on city water. In fact, I personally believe everyone, on grid and off grid, should know what pressures they have at the spigot. For $10 bucks, you can purchase a pressure tester at Home Depot, Lowe's, or online, that you screw onto a water spigot to determine your water pressure. If it is above 55-65 PSI, it needs to be reduced. My city is known to bump it to over 100 PSI in the AM, and without a pressure regulator, you chance blowing your water lines at the weakest point. I know you are probably aware of this info, but I am putting it out to others who have not paid much attention to their water systems.

Remember, this forum has a sister forum, where I am also an administrator, called plumbingforums,com, We have several plumbers ready to answer any questions related to plumbing issues, septic tanks, vent systems, new construction plumbing, etc.
 
kd4ulw said:
Wouldn’t an air pocket in the hot water tank expand more than the water itself causing an increase in pressure? Those tanks aren’t supposed to have air in them.
Click to expand...

Air will compress. Water won't. In the RV, it was like a built in pressure tank. I just didn't know if the same thing happened in household water heaters by design.
 
havasu said:
It is imperative you have a pressure reducing valve if you are on city water.
Click to expand...

Yup, we are on city water. And we have a pressure reducing valve installed. I actually do have a new one of those and that is my second train of thought with what may be causing the higher pressures. A very small leak in that PRV could do what I'm seeing, couldn't it?

I am NOT looking forward to replacing it, mostly because of having to crawl through the dirt and crud of a crawl space to get to it, back out for the tool I forgot, back in to change it, back out to turn the water back on, back in to check for leaks... you get the point. LOL!! I can do it if I hafta...
 
PopPopT said:
Air will compress. Water won't. In the RV, it was like a built in pressure tank. I just didn't know if the same thing happened in household water heaters by design.
Click to expand...
Modern installs include a small expansion tank that has about 1 gallon capacity and has a seal air bladder in it to handle the water expanding when it heats up. My brother gave me one but I never got around to installing it. So the over pressure valve on the side of my heater triggers.

So what you have described is normal.

Pressure regulators

The one on my son's place went bad. He noticed found and fixed a pipe that sprang a leak and soon after another one went. Lather rinse repeat. My brother recognized the symptoms and we measured 165 psi .

Ben
 
PopPopT said:
The relief valve is plumbed to drain under the house. I have seen it drip a little when down under there but it's been a while since I looked.
Click to expand...
I believe that is prohibited by code, since you have no way of verifying increasing pressure. Many also don't realize that some will open the relief valve to test it, but once they do, they rarely will seat without getting sediment in the seal, causing your valve to leak, which causes it to be ruined and will need replacement.
 
havasu said:
I believe that is prohibited by code, since you have no way of verifying increasing pressure. Many also don't realize that some will open the relief valve to test it, but once they do, they rarely will seat without getting sediment in the seal, causing your valve to leak, which causes it to be ruined and will need replacement.
Click to expand...

To be honest, I'm not sure how code sets up a water heater pressure relief drain. There pretty much are no codes here and the house kinda shows that in numerous ways. Whoever did the electrical did a really good job, better than I would have expected. Whoever did the plumbing left a lot to be desired, in more ways than one. (No drain venting for one, which never even showed on an inspection report (sigh)... but that's a different topic.)
 
in my area the code requires a expansion tank on a water heater that is on a system with a pressure reducing valve. Which that is usually a municipal system.
The vast majority of the systems in my area are a private well. We like to install a t&p valve drop about 4 inches from the floor and then take a 3x2 reducing coupling and put that into the floor so to speak, the 2" will go through the floor and the 3 " will be above. Much like a funnel. This way if the t&p drips it will drip into the crawlspace, Also the drip can be seen from above the floor, in addition when the t&p is tested we can see if it shuts properly.
 
Why don't you just shut off the valve on the water heater overnight? By removing the heater from your system you will see if it's the cause of the spike. If you leave the heat on, the T & P valve may release. Turning the heat off or at least down to vacation is probably a better (and safer idea) idea, because your old T & P may not be functioning, since you haven't mentioned it's releasing before and you know your temp got up over it's release point.
I got this answer after I did a search for "hot water pressure increases over night".
 
How can the pressure in your water heater increase? The pressure in the tank cannot exceed the line pressure fed into it. If the water expands with heat (it does marginally) the pressure moves water from the tank back into the cold water supply line equalizing the pressure.

If you are experiencing faster flow when you turn the water on and then it reduces you must have a partial blockage in the hot water pipe. The flow starts out faster because the water fills the pipe beyond the restriction but the restriction slows the flow once the tap is on.
 
SheepDog said:
How can the pressure in your water heater increase? The pressure in the tank cannot exceed the line pressure fed into it. If the water expands with heat (it does marginally) the pressure moves water from the tank back into the cold water supply line equalizing the pressure.

If you are experiencing faster flow when you turn the water on and then it reduces you must have a partial blockage in the hot water pipe. The flow starts out faster because the water fills the pipe beyond the restriction but the restriction slows the flow once the tap is on.
Click to expand...
Water meters have check valves to prevent back flow and possible contamination of the supply lines.

Ben
 
OK, I've never had one apart. Something for my "to do" list. :)
 
The pressure/temperature relief valves on water heaters is generally set low, water heaters are considered "boilers", I ran across this issue when I worked for the local school district, I got dinged by the fire martial for having a p/t relief valve that had too high of a pressure setting. In our home water system I had installed a check valve on the outlet of the water heater to keep heat loss to a minimum, I ended up having to drill a small hole in the valve due to pressures building up in the water heater because of water hammer, never had any pressure problems after that was done. Our water system is gravity flow, the regular pressure is 25 psi but because of the distance from the water cistern to the house, water pressure can go up for a very short period of time, the check valve on the inlet of the water heater kept it from equalizing back to the 25 psi.
 
Once or twice a year you should drain your water heater, turn it off first. at the same time you should test you T&P valve. This is a safety valve that releases if it gets too hot or too much pressure builds up. Scale builds up and will either not close completely or in an extreme case the scale can be bad enough to prevent the valve from opening. In either of these cases your valve is bad and needs replacing. This is normal maintenance. The alternative is to eventually blow up your water heater. When this happens it will take a good portion of your home and anyone who is near by. Testing this valve regularly will delay replacement.

Yes, replacing the T&P valve is a minor aggravation but replacing half your home and family is far more problematic. I've never seen one go but I have seen videos, one of which was of a water heater taking the roof and back wall out of a brick house. A T&P valve is a safety device. Not having a good one is like not having brakes on your truck.
 
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