(The exhaust will be a similar piece of PVC pipe.)The problem with putting a fine screen (like window screen) on these is that the combustion air blower in the furnace is usually sucking quite a bit of air through the intake pipe. 

So, my question now is...what are the toxic ramifications for the combustion byproduct of foam insulation?

In 2002 (or 2003), I renegotiated my rent to $2,150 (dot com bust); although market value was $2,000 the cost of move made me stay.  

They won’t just spontaneously combust on you.  

It was reminiscent of the Dot Com bust!

Definitely vet him (because we know all contractors are males).If you can handle it all, yes I would take the risk and go for it.Taking risks is where you have potential to make money (and lose money and internally combust into a gazillion pieces), but let's be optimistic!

The dot com bust happened in 2000/2001 and we were still growing high double digits before, during and after that time.

The can't load and fire themselves, and they don't spontaneously combust or explode or anything like that.

@Keith LewisIf the upper floor is a separate unit, then the space between it and the ceiling of the lower unit, if properly fire rated will be filled with a non-combustable "insulation" such as rock wool which also provides significant sound deadening.  

The chimney cleaning only prevents the build up of combustibles in the chimney and also gives me a report on the condition of the fireplace and chimney.