Will having an expansion tank on the hot water pipe cause any problems?

Question

I want to replace my water expansion tank and I just found out that it is installed in the hot water pipe coming out from the water heater. From what I've read, it should be installed in the cold water supply. I want to know if this will cause any problems

Answer 1

The only 'problem' is that it fills with hot water. The water sits there and will get cold if not being used.

When the hot water is turned on again, this cooler water will mix with your hot water.

Your hot water will change in temperature a bit until the water in the tank, and the metal of the tank get hot.

Nothing will happen that will ruin your plumbing.

Answer 2

The hot water line is a normal-enough place to install one for hot water expansion (especially if there is a check valve on the line entering the hot water tank, for preventing thermo-siphoning.) It's not be the best choice from a hot water efficiency point of view, though (since the water in the expansion tank will tend to cool, and that means a slug of cold-ish water will come out before any hot water does.)

If using a tank for hot water expansion it can be on the cold feed line, but must be after any check valve. If there's no check valve, it can be anywhere on the cold side.

The cold water line is the typical place to have one for a well-pump pressure system, but that is presumably not the situation you have if the current tank is on the hot water side.

Be sure the tank you replace it with is designed to work with hot water; or move it to the cold side if that's not too inconvenient.