Thread: Expansion tank on Tankless water heaters in attic

Should not the expansion tank have a catch/drip pan underneath it?

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Is that an incoming water line or a hotwater line from boiler or water heater?
If its cold water incoming line the line itself should be insulated to prevent condensation. No drip pan required under expansion tank.

A thermal expansion tank should be mounted vertically ... that one looks to be at an angle (which puts a lot of stresson the ffitting and can break the fitting).

You cannot not trick us with which how you you speak....

Let me me rephrase your question...still the same question, just easier to grasp:

Should the expansion tank have a catch/drip pan underneath it?

Because of the reason Jerry identified above, yes, it SHOULD have a very large drip pan under it. Had it been installed correctly (vertically), it should not need one...nor is it required. Check your local jurisdiction.

Do you have any other photos? I suspect there are other items that aren't just right.

This begs the question...should there be a drip pan under THIS tankless water heater?

Originally Posted by Bill Bryan

You cannot not trick us with which how you you speak....

Let me me rephrase your question...still the same question, just easier to grasp:

Should the expansion tank have a catch/drip pan underneath it?

Because of the reason Jerry identified above, yes, it SHOULD have a very large drip pan under it. Had it been installed correctly (vertically), it should not need one...nor is it required. Check your local jurisdiction.

Do you have any other photos? I suspect there are other items that aren't just right.

This begs the question...should there be a drip pan under THIS tankless water heater?

And you can't fool me with an answer like that. Just what are you trying to impart. Sounds like double talk to me.

The unasked question is: Does a tankless water heater require an expansion tank?

The answer to that would be: Why would it require an expansion tank?

Originally Posted by Jerry Peck

A thermal expansion tank should be mounted vertically ... that one looks to be at an angle (which puts a lot of stresson the ffitting and can break the fitting).

Thanks, Jerry.

Yes, it is at an angle. it is about 4ft from the waterheater

An expansion tank is recommended if there is a one way valve installed on the incoming water line. Several manufactures recommend installation or to local requirements.

Here is an example
http://www.trailappliances.com/catal...NG_install.pdf

Raymond,

That's interesting given that tankless water heaters only operate when the water is flowing - at least that is my understanding of how they operate and why they are not subject to the same requirements that "storage" tanks and water heaters are.

Thanks

Originally Posted by Jerry Peck

Raymond,

That's interesting given that tankless water heaters only operate when the water is flowing - at least that is my understanding of how they operate and why they are not subject to the same requirements that "storage" tanks and water heaters are.

Thanks

Some of the newer models have a recirculation feature and the unit actually has a pump that circulates the water through it. I found one in a home a few weeks ago it has an expansion tank. https://www.rinnai.us/tankless-water...tion-solutions

Originally Posted by Scott Patterson

Some of the newer models have a recirculation feature and the unit actually has a pump that circulates the water through it. I found one in a home a few weeks ago it has an expansion tank. https://www.rinnai.us/tankless-water...tion-solutions

Scott,

That would make it a hot water storage' unit, which would then require a T&P relief valve instead of just a pressure relief valve, wouldn't it?

My 2 cents. There is no need for a thermal expansion device if there is not a storage tank with enough water to expand enough to cause excessive pressure.
My guess is that expansion tank was a leftover from a previous tank style heater.
The drawings I saw of Rinnai installation instructions showing an expansion tank also show a storage tank "sized to meet the standby losses" which would need and expansion tank.
As we know, the expansion tanks should be sized based off the storage capacity of the tank style heater... No storage capacity means no need for an expansion tank whether flowing with a recirculating pump or not. Just my logic and opinion.

That's a Navien unit. The "A" series have a buffer tank and an internal pump to keep the buffer tank up to temp. It prevents the "cold water sandwich" effect, and allows for a trickle of hot water, instead of the .5 gpm normally required to fire a tankless. Because the unit can fire, without an actual draw of water, it's considered a closed loop, and requires an expansion tank.

Similar to the Rinnai, when a recirc line is used, an expansion tank is required.

Originally Posted by Raymond Wand

An expansion tank is recommended if there is a one way valve installed on the incoming water line. Several manufactures recommend installation or to local requirements.

Here is an example
http://www.trailappliances.com/catal...NG_install.pdf

This is the recommendation if you have a water tank. If you do NOT have a water tank, and there is a much smaller volume of water in your system, then how much expansion and therefore how much additional pressure do you expect when the water is heated? If 40 gallons expands to 40.6 gallons (according to another reference I've seen), then how much expansion would you see in a tankless system? Not very much, I would say.

I've read LOTS of comments from professional people saying that an expansion tank is required, and only a few comments that detail the actual requirement for when one is truly required. One thing is for certain though, this "requirement" is good for business. It's good for the initial install, and it's good again a couple of years later when the expansion tank leaks.

A little thread deviation...
I rarely see expansion tanks, maybe a couple a year. I wonder, for those of you that see them regularly, do you check them to determine appropriate air pressure coincides with existing water pressure or disclaim them? If you check functionality, what procedures do you follow? Thanks

If it's a closed system then it needs an expansion tank. Otherwise not. Done.

To check a diaphragm tank it must be isolated from the water pressure. Since very, very few installers think to install an isolation valve between the tank and the system, there is no way to accurately measure the charge in those cases. If you can isolate it, then a simple air gauge will determine the charge, which should be compared against the system pressure. If water squirts out of the schrader valve, the diaphragm blew so it must be replaced.

Ian,

Like Bob stated, difficult to check. Like the condition of the water heater tank or many other items that we just cannot report on in a practical sense. These will typically last as long as a water heater and should be replaced when the water heater is replaced. Other than that...

Originally Posted by Gunnar Alquist

Ian,

Like Bob stated, difficult to check. Like the condition of the water heater tank or many other items that we just cannot report on in a practical sense. These will typically last as long as a water heater and should be replaced when the water heater is replaced. Other than that...

Gunnar, thanks...Do you see them often in N.Ca? Do you disclaim them when you do and move on (With a recommendation to replace when installing a new WH) or at least try to establish some degree of functionality? Obviously if water ejects from the valve the tank is shot. Even some pressure would prevent that but insufficient for the e.t. to be completely effective. Though I suppose anything is better than nothing...

Not to go off thread but I think thermal expansion tanks should be on all water heaters.
For one, to eliminate or reduce water hammer and the effects of water hammer.

Catch pans belong under all water heaters IMO. TPR valves have a way of leaking over time.
If installed in an attic they required by code?
In California they are: 508.4

I jumped on professor Piebody's time machine and
Jerry McCarthy pointed this out in 2008.
professor pie body.JPG

They tried using expansion tanks and air chambers to lessen water hammer but the only things that work are putting water hammer arrestors right at the offending appliances and teaching humans how to close a valve more slowly. Fast closing valves, such as the solenoids on washing machines and dishwashers are big offenders.

Originally Posted by Bob Harper

They tried using expansion tanks and air chambers to lessen water hammer but the only things that work are putting water hammer arrestors right at the offending appliances and teaching humans how to close a valve more slowly. Fast closing valves, such as the solenoids on washing machines and dishwashers are big offenders.

Good point about solenoids, Bob.
Closing valves quickly is not the only culprit as you are aware.
Pipe vibration can be caused by poor plumbing installation practice to worn seats & washers.
Reducing water viscosity to a set pound rate coupled with expansion tanks at/on the hot water side, and arrestors were mechanical equipment is located would limit, even prohibit pipe fitting failures.
The extra cost would be negligible at best.

Thanks Bob.

Originally Posted by Ian Page

Gunnar, thanks...Do you see them often in N.Ca? Do you disclaim them when you do and move on (With a recommendation to replace when installing a new WH) or at least try to establish some degree of functionality? Obviously if water ejects from the valve the tank is shot. Even some pressure would prevent that but insufficient for the e.t. to be completely effective. Though I suppose anything is better than nothing...

Hi Ian,

I see expansion tanks installed on maybe 1 in 10 water heaters... possibly a bit less. I don't think I have ever seen one on a tankless though. I am having trouble figuring out why one would be needed.

I just let them know it is there or let them know if I believe one should be installed. I don't recommend testing or that they will need to be replaced at some unknown point in the future.

Originally Posted by Gunnar Alquist

Hi Ian,
I see expansion tanks installed on maybe 1 in 10 water heaters... possibly a bit less. I don't think I have ever seen one on a tank-less though. I am having trouble figuring out why one would be needed.

Not to answer for Ian but I thought this was covered in a previous thread but I could be mistaken.

From what I understand there are 2 types of tank-less systems. Open and closed.
When there is a closed system with a heating source, there is a chance of pressure increase due to thermal expansion. This is the case with tank-less water heaters installed with a re-circulation loop and a storage tank.

The section 607.3 of the 2012 International Plumbing Code (IPC) provides requirements when controlling pressure from thermal expansion.

Robert,

Thank you. I had not considered a tankless system with a circulation pump. Actually, never seen one. Seems kind of goofy to do that. When someone wants hot water more quickly to the far end of the house, they typically add another tankless. At least, around here they do.

Originally Posted by Gunnar Alquist

Robert,

Thank you. I had not considered a tankless system with a circulation pump. Actually, never seen one. Seems kind of goofy to do that. When someone wants hot water more quickly to the far end of the house, they typically add another tankless. At least, around here they do.

Seems odd to me too, though I suppose there could be an application which might warrant it. Nothing comes to mind (not unusual in many circumstances). The operative word in 607.3 is 'storage' which would not be included in a tankless system.

The question is, still..Does anyone follow a set procedure to determine the efficacy of an installed thermal expansion tank and/or whether its internal pressure coincides with water pressure?

Originally Posted by Ian Page

Seems odd to me too, though I suppose there could be an application which might warrant it. Nothing comes to mind (not unusual in many circumstances). The operative word in 607.3 is 'storage' which would not be included in a tankless system.

The question is, still..Does anyone follow a set procedure to determine the efficacy of an installed thermal expansion tank and/or whether its internal pressure coincides with water pressure?

Actually, there are a growing number of 'tankless' water heaters with a storage tank. So many of these heaters are undersized or under gassed to where they just cannot handle the load in some cases. So, instead of replacing it with a bigger system or increasing the gas piping size or changing it over to a 2 psi system, they simply install a super insulated storage tank and no more cold showers. The WH takes its draw from the tank, which is a lot warmer than the cold inlet. It has a recirculating loop so it can also 'top off' the storage tank. Since these tanks typically lose about 1/4 degree F per hour, the WH rarely has to fire between uses. Also, these tanks can be much smaller than usual.

I don't like tankless for a number of reasons. They are expensive. They require much, much more gas than most contractors will provide or customers pay for, they require annual descaling, which most homeowners bitch about paying for after their first time, the main parts, such as the board, are typically not stocked at supply houses and are very expensive. The venting is often not done properly at best and at worst, a disaster. Oh, yes, unless you have a tank, you won't have potable hot water if the power goes out.

"Actually, there are a growing number of 'tankless' water heaters with a storage tank"

Oxymoron comes to mind....(which, in my case is also one)🤔