Adding expansion tank to water heater

Question

I need to replace my water heater tank since it’s leaking. I’d like to add an expansion tank at the same time. Since space is limited, I’d have to install it horizontally. How high do I need to install the tee adapter on the cold side so the expansion tank can spin during install? Also, it looks like I would need a shorter flexible feed line. What’s the minimum length they’re available in (12 inches?). Would teflon tape and pipe dope be adequate to seal the tee connection and the rest of flexible feed lines? I plan on using a brass tee connector. Should I use a different material? I’m not home and unable to measure the amount of room I have above the tank so I apologize if my questions sound silly. Just trying to get a head start on this. Thanks. enter image description here

Answer 1

The expansion tank can be anywhere that's convenient on the cold water plumbing, so long as there isn't a check valve or PRV between the expansion tank and the water heater.

It does NOT need to be anywhere near the water heater. You don't have much space at all there, from the pictures.

If using pipe dope, don't use tape - pick one, and use it. I currently prefer modern pipe dope. I used to prefer tape .vs. old-fashioned pipe dope. Don't use either on a threaded joint with a sealing washer.

Consider providing a ball valve so you can easily change the tank when it fails in a decade or two.

Answer 2

I wouldn't use flexible lines. I've never seen that on a water heater, only at the end of the line (washing machine, toilet, sink, etc.). The pipes are always under full pressure and a break (and flexible lines are much more prone to bursting than regular pipe) means cutting off hot water to the whole house.

The usual standard for decades in the US has been copper pipe, which means a lot of sweating (soldering) of fittings, but now there are copper press fittings and battery-powered tools to do all the work and it is amazingly fast. I was really surprised what a difference it made when I got my water heater replaced.

As I understand it, the pressure tank can be anywhere because the cold water line is under pressure. With things relating to drains there are a lot of constraints because everything has to be gravity flow. But with water under pressure, location of different components doesn't matter much.

But most important, in my mind, is to do something about the exhaust. Check the installation manual for a new water heater before you buy. And measure carefully. Many have particular rules (which may themselves be part of the plumbing code) regarding (a) vertical distance required before the first turn of the exhaust duct, (b) distance between any exhaust duct and walls, ceilings, etc. What you have right now doesn't look very safe to me.