What is Thermal Expansion?

-  When heated, water expands

-  Under normal circumstances, a 40 gal hot water heater creates roughly an additional half gallon of water when heated (with no demand)

-  In the past this expanded water would flow back into the public water supply

-  However, in many counties, where applicable by code, a backflow preventer is required, creating a closed system and a new problem as this extra half gallon of water must go somewhere since water is not compressible


Zilmet Thermal Expansion Tanks provide a safe, reliable solution for hot water thermal expansion.  Zilmet thermal expansion tanks all come with stainless steel connectors, all have 150 psi max pressure rating and are all NSF 61 certified.


Zilmet Floor Mounted Thermal Expansion tanks all have a side connection for a quicker, easier installation.

Table for pressure v volume for the ZEP1:


Air Pressure (psi)  Volume (mL)
0 173
20 150
40 136
60 91
80 73
100 55
120 18
140 5
150 0