You cannot oversize an expansion tank however you can undersize them.To get the supply pressure inside a home, a home owner can either call a Contractor or follow the steps listed below:Turn off every plumbing fixture in and around the home, including faucets, the ice maker, the automatic pool filler, sprinklers, the dishwasher, the washing machine and the evaporative cooler.Locate the outdoor water spigot closest to the front of the house. If a home owner raises the temperature higher than 140 they may want to opt for a larger size tank. (Factory set point is typically 120 degrees). However, if for some reason a customer has a check valve between the well tank and the water heater they should consider installing a thermal expansion tank between the check valve and water heater.There are a few factors to consider when sizing a thermal expansion tank: Water Heater Size, Water heater set temperature, Incoming Water Pressure, and Air Pressure Set Point in the thermal expansion tank.Water Heater Size & Temperature Set Point:Below is what BackStop, our line of thermal expansion tank recommends for their tanks with the water heater at a 140 degree set point. A well has a well tank that acts as an expansion tank.

The optimum range is 55 to 65 pounds per inch (PSI).Air Pressure Set Point in Thermal Expansion Tank:Once the supply water pressure has been determined the air pressure in the thermal expansion tank should be set. YouвЂ™ll probably see some variation each time. It will land at the number that indicates the water pressure.Repeat the test three times in one day: early in the morning, when you get home from work and at bedtime. They can purchase the pressure gauge from us.Watch the needle on the gauge move.

Cold Water Expansion Tank Installation