Are expansion tanks needed because newer heaters are weaker?

[Seth_Hambrick]

Hey, LLP self employed here. I live in a city where expansion tanks aren't required, although they are in the neighboring city (which has super high water pressure on their main in most areas like 120-180lbs coming in from the main in some areas) and I was wondering.

Expansion tanks are relatively new and Ive noticed all the water heaters ive installed in the past few years tend to leak out the T&P valves without them. But the older models never do this. Has the T&P valves or the water heater tanks themselves just manufactured weaker than they used to be? Or is this all a coincidence? Because I'm starting to think this is just a way for companies to save money on the heater manufacturing and forcing the customer to buy more parts.

 

[RS]

If the incoming water pressure is that high then a regulator is required, and the regulator has a check valve in it. So, when the water heater is filled with cold water, and heats up it expands. Without an expansion tank to absorb this expansion the T&P valve has to relieve the pressure.

 

[Seth_Hambrick]

If the incoming water pressure is that high then a regulator is required, and the regulator has a check valve in it. So, when the water heater is filled with cold water, and heats up it expands. Without an expansion tank to absorb this expansion the T&P valve has to relieve the pressure.

 

[Seth_Hambrick]

Yes, I'm well aware of pressure regulators and install them myself regularly. My question though is why do the new models seem to need them but not the old models? Even with the same pressure

 

[Twowaxhack]

Expansion tanks are for closed systems to give room for expanded heated water. It’s a method of thermal expansion control

Pressure reducing valves are to reduce incoming pressure.

When incoming street pressure is above 80 psi and subsequently regulated by a pressure reducing valve thermal expansion control is required to maintain pressures downstream of the pressure reducing valve when water is heated and expands.

Without thermal expansion control when the water is heated the pressure will spike because the water expands and physically takes up more space. If you don’t provide that space then the pressure will spike.

For the pressure to spike the system must be closed without any leaks.

Any closed system that’s heated will need thermal expansion control even without elevated street pressures.

 

[MicEd69]

50 gallons of water at 70 degrees F will be close to 50.5 gallons of water at 120 degrees F.

If there is a check valve on your incoming water line, like at the meter or internal to the house, you have a closed system. Starting with an empty 50-gallon water heater, that 1/2 gallon of increased volume has to go somewhere. Any water hammer arrestors in the system will take some of the increased volume, and every time you use water, hot or cold, releases a volume of water that has expanded until things come to equilibrium.

So, installing an expansion tank that has an air chamber that is inflated to the inlet water pressure allows the compressible air to keep any pressure spikes at a minimum.

 

[breplum]

Expansion tanks are not relatively new. Not all PRVs have check valves, look for models with Bypass if static pressure is not too bad, like 95psi

 

[MicEd69]

Expansion tanks are not relatively new. Not all PRVs have check valves, look for models with Bypass if static pressure is not too bad, like 95psi

But some water meters have check valves integral or installed by the water company separately. So, in those cases, you will still have a closed system even with a PRV with a bypass.

 

[Twowaxhack]

Technically if your water pressure is above 80 Psi you’d need a PRV and thermal expansion control.

A bypass doesn’t “ count “ when the street pressures are above the max before the bypass becomes active.

Most codes that I’ve read typically do not allow over 80 psi inside the building foundation.

Any closed system that’s heated needs thermal expansion control.

 

[Ludington]

This expansion tank stuff is interesting. I think i understand the need when hooked to an external supply with a check valve. That pressure has no where to go. But when hooked to a system that has a well tank, the well pump has the check valve so extra pressure is going to be absorbed by the well pressure tank. I don't see the need for an expansion tank in this type system. However I've seen it recommended here. Not sure why ?

 

[RS]

No, you don't need an expansion tank on a typical well system, if the pressure tank is large enough. We have always had our own well, and never had a expansion tank for the water heater.

 

[Twowaxhack]

Plumbing code doesn’t recognize a well bladder tank as thermal expansion control. There could also still be a closed system within a private water supply that’s isolated from the well tank and that would require thermal expansion control.

 

[Ludington]

Plumbing code doesn’t recognize a well bladder tank as thermal expansion control. There could also still be a closed system within a private water supply that’s isolated from the well tank and that would require thermal expansion control.

I can't think of how that would be, heater has to get its water from the well tank, which provides the pressure to push it through the system. You would have to cut that connection off to make it be seperated or closed.
Unless you had a seperate pump for extra pressure that pushed it around somehow.
I would think those instances would be very few and far between.
But then.. I'm not a plumber in the real world..what do I know.

 

[Twowaxhack]

I can't think of how that would be, heater has to get its water from the well tank, which provides the pressure to push it through the system. You would have to cut that connection off to make it be seperated or closed.
Unless you had a seperate pump for extra pressure that pushed it around somehow.
I would think those instances would be very few and far between.
But then.. I'm not a plumber in the real world..what do I know.

You could have a hot water circulating system that’s top fed return at the water heater and that requires a check valve to isolate the cold supply from the hot side.

Thats a prime example of how a well system could have a closed hot system.

 

[Ludington]

You could have a hot water circulating system that’s top fed return at the water heater and that requires a check valve to isolate the cold supply from the hot side.

Thats a prime example of how a well system could have a closed hot system.

See, what do I know... , I wouldn't think it would be code, unless something like this was employed. But code is code.. but I wont have one in my house. Not needed in my standard setup.

 

[sarg]

See, what do I know... , I wouldn't think it would be code, unless something like this was employed. But code is code.. but I wont have one in my house. Not needed in my standard setup.

It was also common practice to have a "check valve" installed before the pressure tank ....... that's the way mine was for many years until I learned better and replaced it with a CSV.
The only advantage to that layout was it held pressure in the tank and disguised the fact the check valve at the pump was faulty.

 

[Ludington]

It was also common practice to have a "check valve" installed before the pressure tank ....... that's the way mine was for many years until I learned better and replaced it with a CSV.
The only advantage to that layout was it held pressure in the tank and disguised the fact the check valve at the pump was faulty.

Or a leak in the supply line

 

[Twowaxhack]

If you had 2- 50 gal water heaters with an incoming water temp of 45 and a thermostat setting of 160 degrees and a Constant pressure valve with a small tank, would you need an expansion tank ?

 

[Ludington]

If you had 2- 50 gal water heaters with an incoming water temp of 45 and a thermostat setting of 160 degrees and a Constant pressure valve with a small tank, would you need an expansion tank ?

I'm going to guess no.. because the cpv would regulate the pressure to whatever it was set at. And the well tank should handle the over pressure once the csv stopped pumping. But just a guess

 

[Seth_Hambrick]

If the incoming water pressure is that high then a regulator is required, and the regulator has a check valve in it. So, when the water heater is filled with cold water, and heats up it expands. Without an expansion tank to absorb this expansion the T&P valve has to relieve the pressure.

Yes, I am well aware of this and always instal a PRV to curb the incoming pressure. I should have made this more clear in my post, My problem is even when I get the pressure down to 50psi coming in they still leak overnight