Buffer Tank Question

Roland_18

Hi All,

If I were to use a garden variety "glass lined " water heater as a means to increase the thermal mass of my heating system, would it be necessary to use an expansion tank as well? Also, assuming the water heater is to be used only as a storage tank (electric elements/burner disabled) , how long could I expect the W/H to last? There would be no regular additions of fresh water as it would be a closed system.

TIA, Roland

Mark Eatherton

Tank volume must be taken into consideration on expansion tank sizing...

And you COULD put the exp. tank on the additional storage, but you must make sure that there is only one point of no pressure change (connection point of the actual expansion tank).



Most tanks have a limitation on the tank tapping, which can work against you as it pertains to required flow. You may have to consider piping it in in parallel as opposed to in series..



The tanks should last as long as all the other steel components in the system, in fact longer due to glass lining and sacrificial anode.



ME

Roland_18

W/H Buffer Tank

Thanks Mark.

How do you mean "pipe it in paralell" ?  Also, would I need to install a T/P valve ?

Thanks, Roland

Mark Eatherton

Parallel...

The return main goes past the tank, and both the hot and cold lines of the tank are connected to the main. It would probably be a good idea to put a venturri tee in either the hot or cold connection to insure circulation between the tank and the main while the pumps are on. Otherwise, you'd need a small circulator to move water betwixt the two.



No T&P required as long as there is a pressure relief valve on your heat source.



ME

aemeeich

Parallel Buffer Tank Connection

I just did this exact thing at my own house this spring (still a work in progress though).  I used a 40 gal tank from sears. 



I used the element tappings for the supply/return water piping since they are 1".  I just capped off the 3/4" tappings on the top of the tank.



It is piped in parallel with its own pump so that I can tweak the flow rate and turn it off if it isn't needed.

Roland_18

W/H Buffer Tank

How is the buffer tank circulator controlled?

aemeeich

Buffer Tank Pump

When I hook it up in the next couple of weeks or so, I'm going to start by running the buffer tank pump whenever a zone is calling, it'll be piggy-backed on the system pump terminal of the boiler.

NRT_Rob

if you "turn it off"

you lose 40 gallons of heated water at some point.



I think you'd be best served by just keeping it inline at all times.

aemeeich

Not truly lost in a conditioned space

In my particular case, since all the equipment is located in a conditioned space, it wouldn't truly be lost.

NRT_Rob

ok

then you could say the same thing about the jacket losses of the tank, and then the question is, why take it offline at all?