Big Mouth Vents - How Installed and Vendor ?

JUGHNE

The bolt holes themselves may weaken the existing FJ IMO.
The wood "sandwich" described would only involve multiple self tapping screws which could be installed from both sides of the entire sandwich. Maybe 10-15 high grade screws. They go in well with a small impact driver.

SteamHeat

I will post the exact measurements later for anyone who might benefit from them, but the clearance from the outer edge of the 3/4" threads below the coupler in my family's home piping to the floor joist is only 1/2".

Neither street elbow, not standard elbow could be threaded on without having to carve the floor joist.

A union would also require carving the fj, but to a lesser depth of intrusion. The problem with the union is it is 2" long like the coupler it would replace, and if used with two street elbows, would bring the height up so much that the Big Mouth Vent would be too tall even if a large hole was cut into the ceiling above. The vent would be discharging into the space between floors. If some water accumulated due to wet steam or a partially clogged 67 year old return line, the wood would be frequently wetted.

So I am going back to the original idea of mounting the Big Mouth Vent in place of the Hoffman 4A. I should only need to cut 1/4" into the floor joist an area the size of the mepco hex on the back of the vent. I think it will be a minimal intrusion.

I have ordered 3 of the vents and also a Bondhus 12118 5/8-Inch Long Hex L-Wrench...
https://www.amazon.com/Bondhus-12118-8-Inch-Long-L-Wrench/dp/B001HWG7E8/ref=sr_1_1?ie=UTF8&qid=1484333677&sr=8-1&keywords=5%2F8+inch+allen+wrench

which I hope will fit the tailpiece and also fit into the space I have for tools between the vent and adjacent piping.

1 of the vents I ordered is just in case, the other I will try to get into whatever piping I find underneath the paneling for the second dry return.

Can anyone give me a hint how to get the paneling mouldings off ???

Thanks.