Hot air register inside double wall

[austin]

I was looking for the source of a cold air draft coming from under the kitchen sink. There were pipes going down through the floor into the furnace room and I stuffed the hole with insulation. There was still a draft. I took out the false floor under the sink and discovered water pipes going horizontally through to the dining room. I removed the bottom 16" of drywall along the entire length of the dining room wall and found that the pipes extended across the room behind this wall, then vertically to the bathroom above. This wall is parallel to an exterior wall and there is 6" of space between the two walls. There is no vapour barrier covering the insulation on the exterior wall (other exterior walls in the house do have a vapour barrier). There is an unheated garage under the dining room and kitchen. I also discovered a heating outlet (forced air heating system) between the two walls where the pipes are. The cold draft appears to have come from the space around where the drain coming down from the upstairs bathroom goes through the dining room floor (between the two walls) to the garage ceiling below, and from two other rather large holes in the floor between the kitchen and the dining room. The wood there is rotten, apparently due to water damage some time ago. Everything is dry now. I stuffed all the holes with insulation. Here are my questions: 1) What should I do about the lack of a vapour barrier over the insulation? (2) Should there be a hot air register there behind the wall; is this standard practice? (3) Could I divert the hot air duct (that currently opens into the space between the two walls) into the garage and wrap the pipes between the two walls with heating wires instead?

[HayZee518]

You don't want heat tape on non accessible piping. It's a little late to put a vapor barrier in place on a finished wall. Maybe consider a foaming type insulation and spray it around the piping and in the wallspace. Seal up the large holes with ply and insulation sandwiched between the patch and floor. As far as the ductwork goes - I assume its purpose is to keep the wallspace reasonably warm to protect against frost, but it's really not doing any good for the roomspace.

[austin]

The heating duct was clearly originally intended to heat the dining room because it was boxed in by drywall on both sides of the frame and a 2x4 between the studs about 12" above the floor. Someone had poked a hole (about 4" x 4") in the drywall on the backside of the wall before covering everything up on the front. I guess this was his solution to a problem with freezing pipes, judging from the extent of water damage in there. If I divert the heating duct to the currently unheated garage which, as discussed in a previous post, I want to convert into a shop, I want to be sure that that I don't recreate the original problem. The winter temperature here can go as low as -40. I'll make the repairs as you suggested, but how do I spray foam around the piping and in the wall space? Or do you mean, fill the entire space with foam? Also, I was wondering about replacing that drywall that I've removed at the bottom of the dining room wall (9' long x 16" high) with a grill so that the house air could warm that space. Would that be okay? Or, would that just let too much heat escape from the house?