Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws
As aboveBetter but no each flue joint needs to be accessible so it can be examined for leakage there are specialized boxings made for this purpose. Kop
When you say the boiler should not be in that position are you talking about the boiler or the boiler flue?
Reply to the thread, titled "An interesting condensing flue - would appreciate comments of any kind" which is posted in UK Plumbers Forums on Plumbers Forums.
We recommend City Plumbing Supplies, BES, and Plumbing Superstore for all plumbing supplies.