Which kind of foundation it is
A basement, a slab and a crawl space each need a different layout. A crawl space also needs a vapor barrier over the soil, which adds materials and time.
Ask which foundation type the quote assumes.
What is under the floor
Air moves easily through loose gravel and slowly through packed clay. How well air moves under the slab decides how many suction points a house needs.
A good contractor tests this before quoting.
The pipe route
A short pipe from the basement corner to a vent above the roofline is the simplest case. A longer run through finished rooms or around obstacles adds time and materials.
Ask where the pipe will go and whether it will be visible.
Finishes and where the fan goes
A fan in the attic, in the garage or outside the house all work. Boxed pipe, painted pipe and neat cable runs take extra time.
Compare the finish details before you compare the totals.
Sealing, the sump and follow-up
Sealing cracks and a sump lid helps the fan work well. A follow-up test should be part of the quote.
Ask what is included and what is extra.
