Foundation vents- not necessarily heat related.

SlamDunk

Hello, everyone. Whenever I return home from a week long trip, the house smells like the basement/crawlspace. Not so when we are living in the house daily.
I decided to try removing plugs from the foundation vents to see if it it helps. I noticed the basement portion flooded with fresh air which is what I hoped for. But the internet seems to lean against ventilation. The crawls space is encapsulated. I have a natural gas heater and a rarely used steamer ( it doesnt get that cold down here anymore. I use it for a month each year. The remainder of the year, we use an HVAC system in the attic. I'm wondering if the returns for this system is pulling air up from crawlspace into the house with little fresh make up air? What are your thoughts?

mattmia2

where are these appliances in relation to the sealed crawlspace?(i am concerned about them having enough combustion air)

when the space is heated, that may increase infiltration to the point it dilutes the air from the crawlspace.

alternately when the space is mostly unheated it may have a high moisture content and be growing its own stuff that you're smelling.

SlamDunk

it is unheated and has an Aprilaire dehumidifier that, with plugs in the vents, kept the space under the house at 55% or less. Until recently, I had a remote rh sensor with bluetooth, to monitor the space for about three years to verify this.

The appliances are a nominal 20-30 feet from vents (8 of them). This is a 1930 bungalow- not tightly sealed at all. And the basement is really a pit for the boiler and hw heater. Surrounded by crawlspace. Stuff growing down there? Maybe, but I dont see evidence. That doesnt mean it isn't though. The smell is, i dont know. Earthy? Not moldy ar mildewy.

Jamie Hall

The internet may be against ventilation. You shouldn't be. While you don't need a whole lot of ventilation, you do need some. This isn't a sealed modern house — that crawl space has to breathe.

Kaos

How exactly is the crawl encapsulated? Is there poly on the floor, if yes all seams taped?

If you do vent, the better option is an exhaust fan in the crawl. You want to take nice clean air from the house, pull it through the crawl to pick up any smells and vent it out. You do have to watch negative pressure if you have an atmospheric burner. If you want better, a cheap ERV will give you energy recovery plus fresh air supply to the rest of the house.

EBEBRATT-Ed

I agree that an ERV would be a good idea.

Larry Weingarten

I'd be looking to create a slight positive air pressure in the house. This would prevent much of anything in the crawl from getting indoors. It also could help drive ventilation of the crawl. Aside from that, a thorough sealing of the floor above the crawl would be a good, and probably more difficult approach.

Yours, Larry

ps. Exhaust ventilation of the crawl could work also.

psb75

De-humidification is great. Keep it up., especially in the summer. Mold needs moisture to grow. Sealing between living space and crawlspace is key. DO provide for proper amount of new combustion air. Venting the crawlspace in the summer does allow humidity in.

SlamDunk

@Jamie Hall That was one of my father's mantras, " A house has to BREATHE!". Thanks for that memory.

@Kaos I have had a 500cfm exhaust fan down there for years, on 24/7/365 in a nominal 8000cft area. No help. It has pvc on dirt, seams taped.

HydronicMike

You could check to see if/when your house is depressurizing. Does your whole house dehumidifier have a fresh air damper attached for air changes?

Kaos

500cfm is way too high. Code is 20cfm/1000sqft and usually you can get away with less, could be that you are depressurizing the crawl enough to pull in soil gases. How is the pvc sealed to the stem walls and what is the insulation there.

SlamDunk

https://forum.heatinghelp.com/discussion/comment/1871846#Comment_1871846

It does not. I figured there are enough cavities to the attic for sewer vents to be enough for fresh air make up. The attic is well ventilated. The dehumidifier just recirculates air in the crawlspace/pit. Hopefully, the dry winter air from open vents will help. I'll be able to check when we leave again in December. I put the exhaust fan on a timer. Just on for 10 hours at night. I might turn it off altogether to avoid pulling in fresh air from vents and sending it out with the fan. All trial and error with little success. I appreciate your thoughts.

SlamDunk

https://forum.heatinghelp.com/discussion/comment/1871850#Comment_1871850

that makes a lot of sense. I'll turn it off until I can throttle it. Butyl tape, sealant and ram set nails. It was tough getting any onething to stick to brick. I threw the kitchen sink at it.

Intplm.

@SlamDunk What are you smelling? What does it smell like? Is it musty, damp, mildew, etc.? Or is it a combustion smell left over from a boiler or furnace operating?

SlamDunk

@Intplm. , the house smells "earthy" after being unoccupied for several days. Not moldy or mildew. Only the hot water heater running now and it doesnt run much while we are gone. Not at all a combustion smell.

I think @Kaos and @Jamie Hall nailed it. Yesterday, I removed the foundation vent plugs and this morning, I turned off the exhaust fan.. I wont know how the house smells until I return from my next trip. But one thing I did notice this afternoon is, my radon meter's one day reading dropped from 6 pico to 0.81 pico. The seven day average is still 5.5 but I think that will drop too. This alone is worth leaving vents open and the fan off