A couple of observations: 1. I know of no reason (take that with a grain of salt) why you can't use the spliced approach you propose. But if it were me, I'd use a large junction box rather than making the connection in a pull box. It wasn't long ago when you couldn't use conduit bodies for junctions, but that changed fairly recently (2005 code?). Still, I find the conduit body fill requirements to be confusing and, AFAIK, they only apply to pull boxes, LBs, etc. that are specifically approved for that purpose and marked for volume. Moreover, a junction box would a better choice for securing the outgoing SER with proper clamping. 2. One way to splice the wires is to use old fashion split-bolt connectors. But before attempting to use split bolts, you should be aware that there's some skill involved in taping the connection properly with two kinds of tape built up to at least the thickness of the wire's insulation at all points of the splice. A better choice might be Polaris connectors (see link below). I'd never heard of them until one of the members here mentioned them in another thread. (Thanks, Petey Racer!) They may be a bit more expensive than split-bolts, but they take less time to install and are probably better suited to a DIY job as well. I've only used them twice so far, but I like 'em. 3. Since you mention that you're planning to feed a 100-amp subpanel with #4AWG/CU wire, it's worth mentioning that although a special NEC table may permit this for up to 100A for interior subpanels, not all local jurisdictions accept that interpretation. If you really need all that ampacity in your kitchen subpanel, then it'd be a good idea to verify that your AHJ will approve it before you buy any wire. Otherwise, if you don't need the full amperage, you could take a more conservative approach and protect the circuit with a 70-amp breaker in the main panel. Here is a link that might be useful: Polaris connectors

I spoke with the licensed electrician at work this morning regarding my options. He recommended two ways of doing it. 1. Run SCH80 conduit as you recommended from inside the basement across the ceiling to the wall above the panel. Use a sweeping 90 to enter the sheetrock of the wall and down to the panel. Use individual THHN conductors. I need clarification if I can use a single color and mark the terminations with appropriately colored tape. It will still require some patch work on the wall, but much less than patching 10 holes in the ceiling from drilling joists. 2. Use SER cable and exit the sheetrock at the ceiling above the panel. Run the cable across the ceiling and attach with SER staples/clips and go through the sheetrock/joist into the basement. 3. I guess I could still use conduit and still run all my new feeds back to the panel, but that limits expandability later. I also don't know exactly what I want to run yet.

Sorry, I missed the last two posts until now. Spencer, I already have a wireless CO detector at the top of the stairs, which is just off the two bedrooms. This is monitored by my security alarm system. I have a battery operated smoke alarm device in centre of the first floor hallway and another at the base of the stairs in the basement. They are all basically centrally located on each level, "stacked" vertically at the base and top of stairwells. The house has a small footprint. for instance, the boiler unit is located no more than 15 feet from the basement device, and the two bedroom doorways are located about 5 feet from the second floor device. The perimeter walls of the house are not more than 15 feet away in any direction. greg, you are right, I should have advised, but re Canadian Code, I don't see anything here that would be contrary. Ted

Where is your main panel? You can put a sub-panel anywhere that you have good access. Ideally I like to put them as close to the main as possible, but where they meet the needs of the new circuits. When I put a subpanel in a new addition I added on to my house, I ran the sub to the new garage which allowed easier access to run all the new circuit. However, the cost of the wire to run from the main to the sub was costly.