I don't know what San Diego's particular requirements might be, but suggest the following. Screws can ensure that ducting doesn't separate. Rubber lined clamps such as go with the Fantech parts don't need screws. The choice of having the duct section female ends at higher elevation than the male ends will help keep any grease accumulation from leaking out. (If this were a commercial application, the ducting would have to be steel, welded at the connections, and provided with clean-outs. kas

Your furnace would not run properly if the pipes were not sized properly. Is your furnace giving you problems? The installation manual will have a sizing chart in it. Every manufacturer is different. For the brand that I install, the size seems right.

I'm installing a basement bathroom in my 1925 house in Minneapolis. I've just opened my floor and found my main sewer line buried 6 inches below the slab. I'm pretty sure that is deep enough. Now I just need some help laying out the fittings. Since I have such limited space I can't really add alot of vent pipes but I'm not sure I need to since all the fixtures are so close together. My original plan was to have a vent for the toilet, vent for the shower and a separate drain for the sink and laundry. All would drain into the 3" pvc pipe from the toilet. However, when I started picking out fittings I realized I really don't have room for all those pipes. Here is my new plan. The right side of the drawing represents the wall and the left side is the floor. The scale may not be accurate but the measurements shown are accurate. Does anyone have any thoughts on this? Thanks.

Ok, first of all, your plumbing codes are going to be different than mine, but I think you'll want to call a plumber or talk with your local inspector. There are a number of things you have that wouldn't fly in my area, but may be ok in yours. To answer your question though, you'll probably need to stick with the 2" vent for the bathroom.