Preventing thermosiphoning out of storage

[Jackpine Savage]

I'm working on piping and I'm concerned about thermosiphoning in the 1 1/4 copper lines going into the top of my unpressurized tank. I'll have about 3' of line running up to the primary loop which is about 36 feet of copper connected to two boilers. That includes both supply and return. My secondary loop is lower than the primary so I should have to worry about heat migrating into that.

I've seen the drawings that show the dual weighted check valves on the supply side. Has anyone done this? Does it seem effective? I'm thinking that thermosiphoning could occur within the return line as well, especially with 1 1/4 copper, so wouldn't you want to do this on both lines?

The other options I can think of are:

1. Minimize the losses by insulating the pipe. That is simple to do, which I like.
2. Plumb a heat trap loop in both lines above the tank. Cost is some copper, fittings, additional head.
3. Put zone valves on both lines just above the tank. This costs more money and complicates the controls.
4. I suppose in the summer when I'm most concerned about heat loss I can shut off the ball valves above the tank and make sure I open them before firing the boiler. (I'll be getting DHW from the tank)

Other options? Am I being overly concerned about this?

 

[NHFarmer]

I plumbed in a heat trap on my tank.I come out the top of my tank then turn 90* and drop down 18" then two 90* bends then back up to the top and out to the boiler,Seems to work for me.

 

[jekmech]

I used the dual weighted flow check design in my storage tank system and it has worked without a problem since October. Initially there was some chatter from the flow checks that resolved itself after a day or two of the system being fired. I attributed it to an incomplete air purge and suspect the SpiroTherm air eliminator did its job and took care of the problem. See my photos at http://jekmech.photoshop.com to see how I piped it.

 

[Duetech]

That's a real nice looking set up jekmech.

 

[Blevesque]

As NHFarmer stated a thermal trap works great. Here is a picture of mine.