Expansion Tank

I've read a lot of good advice on this board about expansion tanks, and I'm figuring my case is just different enough to warrant a thread...

My main is running into a manabloc pex distribution system, which feeds the cold inlet of the water heater and this then sends the hot back to the manabloc for distribution but not before the hot supply is Tee'd to feed my radiant floor application.

I KNOW I need a expansion tank, and per the Takagi TH1 heating/domestic plumbing map it shows it mounted on the cold main inlet tee'd with the return from the radiant floor application, with check valves throughout the system.

This all makes sense to me, and I was already to put my tank on the main-in side near the water heater, but the guy from Manabloc mentions the expansion tank should go on the HOT outlet line.

My questions are:
1) is this guy correct?
2) Do i need 2 tanks one cold line, one hot?
3) Would you recommend the expansion tank before or after the manabloc distribution system?
Thanks!
kurt

If the heater is stictly used for radiant heating and not for potable water, then you need an expansion tank on the hot (closed) side that is rated for hot water. You shouldn't need one on the cold side. If the heater provides both, then you need a potable water one on the cold side and a boiler one on the hot side (this assumes there's a heat exchanger keeping things separate). Make sure that the pressure is adjusted properly in each...the potable water one typically would be much higher pressure than the boiler side (often around one atmosphere - 14-15#).

hmmm.

OK, so my water heater will supply both domestic supply and radiant flooring. And I don't have a heat exchanger, Takagi didn't mention anything about it, so I need 2 tanks and heat exchanger?

Maybe a visual would help? Will this config work?

tank

IF the domestic water system does not have a pressure regulating valve or a check valve after the water meter, then you do NOT need a domestic expansion tank. AND if the heating system runs at the same pressure as the domestic water lines and does not have a regulator/automatic feeder valve, then it also does NOT need an expansion tank. Expansion tanks are ONLY required when something is installed to make a closed system preventing thermal expansion from being disipated into a larger system. The expansion tank can be installed ANYWHERE in the closed system since pressure is equal everywhere on the same level in the system .

hj said:

IF the domestic water system does not have a pressure regulating valve or a check valve after the water meter, then you do NOT need a domestic expansion tank. AND if the heating system runs at the same pressure as the domestic water lines and does not have a regulator/automatic feeder valve, then it also does NOT need an expansion tank. Expansion tanks are ONLY required when something is installed to make a closed system preventing thermal expansion from being disipated into a larger system. The expansion tank can be installed ANYWHERE in the closed system since pressure is equal everywhere on the same level in the system .

Click to expand...

This is a great reply, thanks! I have check valves throughout the system after the water meter.

The heating system will be supplied by the water heater, but forced through the zones by a Taco 008 series pump, I have a differential bypass valve between the hot supply and cold return on the radiant floor system (cold supply leads to the expansion tank noted in the visual above).

I'm hoping that takes care of it, thanks!!