Expansion tank- DHW

Kungur · Post by **Kungur** » Mon. Dec. 24, 2018 9:11 am

I was just watching a video about potable water expansion tanks.
My boiler has a coil that I have connected to my electric hot water tank,the elements are switched off, via a small circulator. We have warm/hot water coming out of certain cold cold water faucets. So now I understand that the hot water is expanding and the expansion tank deals with it.
So how crucial/important is this tank? Is it something I "must/need" to do?
Thanks!

lzaharis · Post by **lzaharis** » Mon. Dec. 24, 2018 9:15 am

Typically an expansion tank on a hot water heater is used on a municipal water hook up with higher pressures. I have never needed an expansion tank on my hot water heater loop.

nepacoal · Post by **nepacoal** » Mon. Dec. 24, 2018 9:19 am

I wouldn't think hot water expanding is the cause. I would think hot water rises, and hotter water rises even faster. Plus, could the small circulator you are using be pushing water up into the cold water pipes (like ghost flow).

Post by **StokerDon** » Mon. Dec. 24, 2018 9:34 am

Kungur wrote: ↑
Mon. Dec. 24, 2018 9:11 am
My boiler has a coil that I have connected to my electric hot water tank,the elements are switched off, via a small circulator.

I don't understand why you would have to pump water from the DHW coil to the water heater. Normally your well pump or municipal water pressure would handle this. Your going to have to give us a bit more info so we can understand your system.

In general, DHW expansion tanks are only needed when there are check valves in your domestic hot water system. In this case you also need a PRV.

-Don

hotblast1357 · Post by **hotblast1357** » Mon. Dec. 24, 2018 11:01 am

Really the only reason for a expansion tank is on a system fed by a well, so that the well pump does not cycle every time water is used.

Post by **StokerDon** » Mon. Dec. 24, 2018 11:07 am

hotblast1357 wrote: ↑
Mon. Dec. 24, 2018 11:01 am
Really the only reason for a expansion tank is on a system fed by a well, so that the well pump does not cycle every time water is used.

That is something very different than a domestic hot water expansion tank. If there are check valves in the hot water system the heated water needs a place to expand.

-Don

CapeCoaler · Post by **CapeCoaler** » Mon. Dec. 24, 2018 10:08 pm

He has a coil circulating the DHW to a storage tank...
Probably a Taco 006-4b...
Bronze pump no rusting...
Usually has a check valve installed to prevent back flow into the cold supply...
Expansion tanks are recommended in this case because...
The heated and now expanding domestic hot water...
Has no cushion of a private or municipal water system...

A potable hot water expansion tank may be required to offset heated
water expansion. If there is a back flow preventer or any other type
of no return or check valve in the system a thermal expansion tank IS
MANDATORY. The expansion tank must be sized for the entire water
volume of the hot water system. A weeping relief valve indicates the
need for an expansion tank. See the Typical Expansion Tank example
in the Piping section for details.

The 2012 International Residential Code (P2903.4.2) requires the installation of an expansion tank on a hot water tank where thermal expansion may cause an increase in pressure. The tank is only required when the water supply system incorporates a backflow prevention device, check valve or similar device. Similar language can be found in the Uniform Plumbing Code under section 608.3.

Kungur · Post by **Kungur** » Tue. Dec. 25, 2018 8:42 am

I am not on a municipal water supply. We have a well and my pressure tank is an 80 gallon unit.

CapeCoaler · Post by **CapeCoaler** » Tue. Dec. 25, 2018 12:29 pm

If there is no check valve or backflow preventer on the circulation loop...
The well tank acts as an expansion tank...
Same if you are on municipal water...