Compare guides

Comparisons are only useful when the numbers are comparable. Every table on this site puts installed cost, running cost and the work included side by side, so a cheaper system that needs a second suction point does not look cheaper than it is. Start with the two that decide most projects: sub-slab against sub-membrane, and a DIY test against a certified one.

System against system

	Sub-slab (basement/slab)	Sub-membrane (crawl)
Installed band	$800–$2,500	$1,100–$3,000
Suction field	Soil under the slab	Soil under a sealed membrane
Running cost	About $127/yr at 80 W	About $127/yr at 80 W
Common failure	Too few suction points	Unsealed membrane

Full foundation comparison →

Fan size against running cost

Fan power	Annual kWh	Cost at 18.16¢/kWh
60 W	526	About $95
80 W	701	About $127
90 W	788	About $143

EPA budgets $50–$200 a year for fan operation. The difference between a small and a large fan is smaller than the difference between one electricity rate and another, which is why the rate you pay matters more than the fan badge.

DIY test against certified test

	DIY short-term kit	Certified measurement
Cost	$15–$45	$150–$250
Paper trail	Lab report	Chain of custody, signed report
Accepted at closing	Usually not	Yes
Best use	First look, post-install check	Real estate, mitigation baseline

What testing costs by state →

What a comparison cannot settle

Which contractor is competent, whether the roof penetration is easy, and how the soil will behave under suction. Those are site facts. A comparison can tell you what a fair band looks like; it cannot tell you which bid is honest. Ask for the suction-point count, the fan model and the post-install test in writing, and the two questions answer themselves.

Frequently asked questions

Which system costs the least?

A passive system in new construction, at $500–$1,500 with no fan. Among retrofit systems, sub-slab depressurization is the least expensive at $800–$2,500.

Does my state's zone affect the price?

Not directly. The foundation sets the band. Zone 1 counties simply have more homes above the action level, so there is more testing and mitigation activity and usually more contractors competing.

Is a more expensive fan worth it?

Only if the system needs more pressure or the house is larger. For a typical single-point basement system, the standard 60–90 W fan is right, and the running-cost difference between models is a few dollars a month.