Crawl Scape Ventilation

[marc417]

marc417 (Mechanical) Oct 24, 2006
Could anyone please suggest what is the best approach for ventilation of a seasonal residence. A bungalow. Basement is half crawl space, other half is unfinished basement. Its located near St. Lawrence River (winters -20F, summers +90 F and up to 90% hummidity). The place is shut down Dec-May. Crawl space is properly sealed with vapour barrier.

In May to Nov is it better to leave basement & crawl soace vents open to allow natural ventilation, or close all windows/vents and run a dehummidifier (probably allow a bit of opening (10% of what code specified for fresh air only)?

What about when the place is shut down? Is there a need for mechanical or natural ventilation, or can the basement vents be closed? Dehummidification will not be possible as dehummidifers don't run once temp drops below 40F.

How about running a dehummidifier on the ground floor or allowing natural ventilation on the ground floor?

Any suggestions would be appreciated.
Thanks in advance. Marc N.

[teddy bear]

With the earth covered with plastic, suggest keeping the vents closed all the time, winter and summer. Set the dehumidifier at 50-60%RH. When the outside dew point drops below 40^F, enough dry outside air infiltrates the basement to keep the indoor %RH low enough to avoid mold. This assumes that you are maintaining +55^f in the space. Evidence of inadequate ventilation is condensation on the cold exterior surfaces. Slightly increase ventilation to the point that condensation stops. Residential dehus don't function well at <55^F. TB

[RoBoTeq]

Hey marc; I am curious, just what does an HVAC consultant do? I consider myself an HVAC consultant most times, but I have also been in every aspect of the industry, giving me an insight on how to consult. What is your history in the HVAC industry? Thanks, Robin

[cem-bsee]

only open the vents if outdoor RH% is BELOW 55%!

most of us do not know the OD RH% in your area.
\
we here in Huntsville AL have "low" OD RH% when it is <85%!
at 9am = RH=80%, 48F
accordingly, my craw vents are closed with Styrofoam with cracks spray foamed -- run dehum 24/7, since crawl seldom <50F.

[Pschneid]

Latest consensus on crawl space is to keep it sealed, no ventilation. Vapor barrier stops moisture from soil. Opening vents to crawl space only allows more moisture/humidity to enter.
May to November, run dehumidifyer in basement. Humidity always migrates to cooler basement.
Vist residence often enough to check for necessity of running heat during cold evenings and cold days.
Keep house ventilated ie: windows open, during warmer days while occupied.
December to May, visit residence often enough to determine if condensation on exterior walls requires heating unit to be run to prevent moisture damage.
Owning a seasonal residence requires that it NOT be left without attention. Seasonal residences if left unattended are a target for vandals, thieves, burglars, nosey neighbors, and mother nature.

[marc417]

I did not mean any disrespect to any consultants, colleagues, or members. I studied HVAC as part of my mechanical in colleage and only worked on very specific narrow area (compressors for specialized apps)! I'm a newbie when it comes to residential, as I don't know much beyond whats in the building code! Thanks for the replies!