Wich line to tap into?

Got my LP backup boiler today , have three choices for install.

1 Garn side of the heat exchanger unpressurized,

2 Supply line pressurized.

3 Return line pressurized.

The Lp boiler is a Burnham cast iron 105k btu holds 3gal going to install in the same building as the garn. I'm installing this so I can get away and not freeze up. I ran scenario #2 by Heaterman with the water continuously circulating through the backup, he said it would work. But before I start cutting back iron is it the most efficient ?

I would follow Heatermans advice on how to tie it in, he is the best at knowing all things Garn. Plus I would avoid #1, since you dont want to use LP to keep all of your stored water hot, right?

Thanks Clarkbug, My only concern is that with such a small amount of water to heat it would be 180 degrees going into the in floor compensating valve. The highest I've had it was 140 on a -20 day and the floor got to 88.

That is a valid point ward.... You might get other responses if you posted a diagram along with your options.... Its hard to say what is best without knowing what your system is up to....

The LP boiler should be on the pressurized side of the HX.

I'd stab it into the supply going to your load using an aquastat to fire the burner and the pump. You should probably make sure to incorporate some kind of low temp protection for the Burnham. The above mentioned aquastat would look at the temperature coming from the heat exchanger going to your load and fire the Burnham when needed to maintain your desired house temp. The residual heat "left over" will start going to the Garn via the HX whenever it drops below what the Burnham is running. Heat exchangers go both ways. Always hot side to cold side.

Thanks Heaterman, I'll put it in the supply,had planned on an aqua stat but I don't know what you mean by low temp protection. K