domestic water line to barn next to boiler return line

going foam in trench route for boiler run to house from barn. already have water line to barn but it will freeze if not blown out with air for winter. thinking of zip-tying or strapping a 3/4" domestic PEX line to the 1-1/4" return line that will be going back to storage. other than being a small heat sync until domestic line is heated up and potential supplying scalding water to barn, does anybody see a problem with this? i do not want to have to dig below the frost line and i am just looking to get freeze protection by piggybacking next to the return line.

Done that many times up here where frost can go to 5-6' some winters..

You can get some serious temperatures out of it when you first turn it on so watch yourself. It's usually not an issue.

thanks. i also see a lot of people line the trench with plastic so as not to contaminate the foam with dirt as it is being sprayed. is this necessary?

I would try and keep foam from being contaminated. Think of this. You are using closed cell foam and trying to keep ground water out. CC foam does not absorb water, but if it has dirt mixed in with foam, the dirt creates a void for water to get in, enough voids and your whole system if void. My 2 cents. Foamit UP

The plastic costs almost nothing and goes in fast. As important as this system component is for your system it's very cheap insurance to make sure you get the maximum value from your foam contractor.