Thermostat mount air leak

Turbo Dave

Hello all. I am replacing several dozen thermostats in an old school. The wind coming through the metal electric boxes they are mounted upon must be stopped. What is the most effective solution to this problem? Thank you.

PC7060

The best thing I’ve found is dense packing fiberglass insulation into the box and cavity. It’s an approved fire block and is a very good job stopping air movement.  Fire retardant spray foam is also an option but it’s a real pain later if you have to get back into the box

ChrisJ

At my own house I've used Aeroflex pipe insulation foam.
Much nicer to handle than fiberglass and blocks air better. Some of the 3/4" thick stuff works well. McMaster has that as well as other types of similar foam.

However, it's certainly not a fireblock.

chief

For air flow blocking in electrical conduits per code we use duct seal. Sold in 1# blocks. Available at some big box stores and at electrical wholesale houses.

mattmia2

If the box is removable wrapping the outside with a sheet of polyethylene and sealing around the tubing or cable is also an option. Lining the box with sheets of sealant like what is used to flash window also would seal it up.

PC7060

“For air flow blocking in electrical conduits per code we use duct seal.”
@chief makes good point.  Good material and is only correct solution if line voltage is present in box.  

Not code required assuming low voltage only. 

mattmia2

PC7060 said:

“For air flow blocking in electrical conduits per code we use duct seal.”
@chief makes good point.  Good material and is only correct solution if line voltage is present in box.  

Not code required assuming low voltage only. 

I was thinking low energy or pneumatic, but you have far fewer options if it is line voltage.