Expansion Tank for Two Independant Water Heaters

[walton80]

I recently installed a water pressure booster pump which contains an internal check valve, thereby creating a closed system in the home. I understand that an expansion tank should be installed for hot water expansion between the check valve and hot water heaters.

Our home was Buit in 1978 and contains two independent hot water heaters each with dedicated plumbing lines. There is a 50 gallon tank dedicated for downstairs and the kids bedrooms and a separate 75 gallon tank that provides hot water to the upstairs master bathroom and laundry room. This configuration seems neither series nor parallel if I understand correctly.

My plumber said that we would need to install 2 separate expansion tanks, one for each heater, which does not make sense to me. It seems to me that one larger expansion tank would be sufficient because the pipes are eventually connected in the same system.

Can anyone offer some advice if one large expansion tank would offer the proper protection for thermal expansion of both heaters?

 

[RS]

I would think one expansion tank would suffice, as long as it's big enough, and there are no other check valves in the system. I believe it should be in the cold-water line near one of the heaters. We have 2 water heaters in series, but we have a well with a pressure tank that acts as an expansion tank, and it works fine.

 

[MicEd69]

I recently installed a water pressure booster pump which contains an internal check valve, thereby creating a closed system in the home. I understand that an expansion tank should be installed for hot water expansion between the check valve and hot water heaters.

Our home was Buit in 1978 and contains two independent hot water heaters each with dedicated plumbing lines. There is a 50 gallon tank dedicated for downstairs and the kids bedrooms and a separate 75 gallon tank that provides hot water to the upstairs master bathroom and laundry room. This configuration seems neither series nor parallel if I understand correctly.

My plumber said that we would need to install 2 separate expansion tanks, one for each heater, which does not make sense to me. It seems to me that one larger expansion tank would be sufficient because the pipes are eventually connected in the same system.

Can anyone offer some advice if one large expansion tank would offer the proper protection for thermal expansion of both heaters?

You have 125 gallons of hot water that needs to be considered. You will likely need at least a 5-gallon expansion tank for that system. The plumber may be thinking a 2-gallon tank for the 50-gallon water heater and a 3-gallon tank for the 75-gallon water heater would be better/easier than a larger single tank. But as long as you have ready access and no check valves in the piping system that would isolate the water lines, a single tank would seem to work provided it is sized right for your operating conditions.

 

[Twowaxhack]

I’d use one tank and I’d install it inside the closed system in a location that wouldn’t be damaged when it eventually leaks. That’s my best advice.

Sizing the tank depends on several factors and depending on how the manufacturer designed the “ recommended “ size tank will dictate the size.

Size of tanks/system
Temp of incoming water
Temp of water at thermostat setting
Operating pressure
What you ate for breakfast
Etc etc. you get the idea.

 

[sawsaw]

[QUOTE="MicEd69, You have 125 gallons of hot water that needs to be considered...

125 gallons?? Wow! That makes me curious ... my family, numbering six on average, had no issues being supplied hot water from a 40 gal. HWH. That, coupled with a mother who washed, washed, washed has me wondering why 125 gal. of hot water has been installed. Anybody???

 

[RS]

[QUOTE="MicEd69, You have 125 gallons of hot water that needs to be considered...

125 gallons?? Wow! That makes me curious ... my family, numbering six on average, had no issues being supplied hot water from a 40 gal. WTH. That, coupled with a mother who washed, washed, washed has me wondering why 125 gal. of hot water has been installed. Anybody???

That's my first thought, I can't imagine needing that much hot water! Maybe they are on off-peak power, so they are not energized at peak times?

 

[Twowaxhack]

Big tub

Teenage girls

Frequent guests

Etc etc

Many reasons for big demand and that’s where a tankless shines.

 

[MicEd69]

[QUOTE="MicEd69, You have 125 gallons of hot water that needs to be considered...

125 gallons?? Wow! That makes me curious ... my family, numbering six on average, had no issues being supplied hot water from a 40 gal. WTH. That, coupled with a mother who washed, washed, washed has me wondering why 125 gal. of hot water has been installed. Anybody???

With a 75-gallon water heater supplying hot water to the Master bath and laundry, I'm thinking perhaps a Jacuzzi tub in the Master Bath. And if the "kids" are teenage girls, that 50 gallons of hot water could be for a single shower, LOL!

 

[Twowaxhack]

The thermostat setting and the incoming water temp play a part in how much standby capacity you need.

100gal at a thermostat setting of 120 and incoming water temp of 50 degrees isn’t going to go far.

100 gal at a thermostat setting of 150 and incoming water temp of 75 would be a world of difference.

 

[GReynolds929]

A 40 gallon water heater will supply two 5-10 minute showers back to back at best, if showers and laundry are staggered it can keep up fine. With today's general use a 40 gallon is small.

 

[RS]

A 40 gallon water heater will supply two 5-10 minute showers back to back at best, if showers and laundry are staggered it can keep up fine. With today's general use a 40 gallon is small.

At our winter home in Arizona, we only have a 20-gallon heater, and we get along just fine, 2 people showering, laundry, and a dishwasher, but here in Arizona we shouldn't be wasting water!