Dehumidifier Installation
In the humid Pacific Northwest, a dehumidifier is often necessary to maintain healthy relative humidity levels year-round.
Humidity management is the operational heart of any crawlspace encapsulation system. Sealing the crawlspace envelope stops the major sources of moisture entry, but the residual humidity in the sealed space — from the soil itself, from diffusion through concrete stem walls, and from any minor air leakage — needs somewhere to go. In most Lower Mainland crawlspaces, a properly sized commercial dehumidifier running continuously is the right answer. The target is to maintain relative humidity at or below 50 to 55 percent year-round, which is the threshold at which mold growth and wood-boring insect activity become effectively impossible.
The dehumidifiers we install are not consumer units from a hardware store. Residential dehumidifiers are designed for above-grade conditioned living spaces and are not built for the temperatures, access constraints, or continuous-duty cycle requirements of a crawlspace. The commercial units we specify for crawlspace use are rated for operation at lower temperatures (some down to near freezing), have higher capacity relative to their physical size, include built-in humidistats that are accurate at the lower end of the humidity range, and have drain connections that can be routed to gravity discharge or a condensate pump rather than requiring manual bucket emptying.
Proper sizing is critical. An undersized dehumidifier will run continuously without reaching the setpoint humidity level, eventually burning out its compressor. An oversized unit is not a problem in terms of dehumidification, but it costs more upfront and uses more energy than necessary. We calculate required capacity based on crawlspace square footage, current moisture load (as measured during inspection), the vapor barrier coverage and sealing quality, and the seasonal humidity patterns typical for the specific location.
Once installed, the dehumidifier should require minimal ongoing attention if the drainage is set up correctly. We route the condensate line to gravity drain wherever possible — directly to a sump pump pit or through the foundation wall to daylight — so the unit runs indefinitely without service calls. Units with internal timers and humidity logging give homeowners and technicians a record of performance over time, which is useful for confirming the system is working as designed and for identifying if conditions change.
Common questions we hear: do I need a dehumidifier if I have good ventilation? In a sealed, encapsulated crawlspace, there is no ventilation — the vents are closed — so the answer is yes, you need active humidity control. Do I need a dehumidifier year-round in BC? Because our mild winters still deliver significant rainfall and our crawlspace soil temperatures stay relatively stable, yes, a dehumidifier should run year-round, though it works hardest during the wet season.