2 water heaters piped together

I’ve never seen this with two water heaters. The hot water of the first goes to the cold water of the second. Is this allowed?

water heaters.JPG

Not a problem though I like to see more isolation valves.

Yes see …http://www.nachi.org/forum/f79/two-water-heaters-79107/#post1002968

What you’re showing is called Series Installation. It’s allowed. There are different opinions of it’s value of operation.

It’s looks like these are 40 gallon tanks. Unless the hot water demand at this house requires that much hot water to be available, you may recommend turning off the gas supply to the upstream water heater.

This link describes both series and parallel WH installation.

It’s OK, a common application is in a multi-unit property. Like a complex where there’s one water heater for several units. For a single family likely overkill, but allowed just the same.


When using the residential sizing, you will find 2 water heaters recommended quite often with larger homes and a family of 4 or more.

Most single family homes that I inspect have multiple water heaters.

Typically 3, 3 1/2, or 4 full bath’s will have 2 wh’s.