Thermal Trap - Plumbing Zone

Miguel · 01-27-2010, 12:21 AM

Oh I remember now! I just read a post about thermal expansion and it jogged my tired old head into what it was I wanted to find out before thursday!

We all know the principal of thermal traps on water heaters and such, ie: make a drop 18"-20" on the CW and HW on a water heater and it'll prevent thermal cycling, or migration.

But does anyone here know of an actual formula or what-have-you that would dictate the actual drop required based on a certain temp. rise?

The reason I ask is that a buddy of mine who just lost his best heating guy has asked me to step in and help with a boiler install he has planned this week. It's an awesome job in a 150 yr old brick house with an old pancake style coal-fired gravity HW sytem. Really cool setup and exquisitely maintained over the years. (I tried to get pics but I'll need better lighting and a better camera).

So the problem is we'll have water heated to potentially 185°F at an ambient of about 68°. The boiler will be setup to maintain heat dependant on an outdoor temp of -40°.
Space is limited so what's my minimum trap depth (height?) to prevent migration of the heated water?

Edit: We're deep-sixing the old pancake boiler, FYI.

breid1903 · 01-30-2010, 02:33 PM

go over to www.heatinghelp.com. the wall. do a search. i can't remember and i'm to lazy to look in my books. 36" on boilers? i think. i will tell you that boilers don't always read the book. i had and only one that had a 40" loop on it. didn't work. had to bust piping and a check valve. lol. breid...............

01-27-2010, 12:21 AM	#1
Miguel Drained Professional Join Date: Aug 2009 Location: Sunset Country, Ontario Posts: 709 My Photos	Thermal Trap Oh I remember now! I just read a post about thermal expansion and it jogged my tired old head into what it was I wanted to find out before thursday! We all know the principal of thermal traps on water heaters and such, ie: make a drop 18"-20" on the CW and HW on a water heater and it'll prevent thermal cycling, or migration. But does anyone here know of an actual formula or what-have-you that would dictate the actual drop required based on a certain temp. rise? The reason I ask is that a buddy of mine who just lost his best heating guy has asked me to step in and help with a boiler install he has planned this week. It's an awesome job in a 150 yr old brick house with an old pancake style coal-fired gravity HW sytem. Really cool setup and exquisitely maintained over the years. (I tried to get pics but I'll need better lighting and a better camera). So the problem is we'll have water heated to potentially 185°F at an ambient of about 68°. The boiler will be setup to maintain heat dependant on an outdoor temp of -40°. Space is limited so what's my minimum trap depth (height?) to prevent migration of the heated water? Edit: We're deep-sixing the old pancake boiler, FYI.

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01-30-2010, 02:33 PM	#2
breid1903 Senior Member Join Date: Feb 2009 Location: fulton, indiana Posts: 600 My Photos	go over to www.heatinghelp.com. the wall. do a search. i can't remember and i'm to lazy to look in my books. 36" on boilers? i think. i will tell you that boilers don't always read the book. i had and only one that had a 40" loop on it. didn't work. had to bust piping and a check valve. lol. breid...............