Cockamamie Scheme #4342
My house is 112 years old. I was in my attic and soaking my shirt because it was 120° in there (I live in Florida). I thought how nice it'd be to get some fresh air in there. I thought it'd be even better if I could get that air from the (somewhat) cooler air in my crawlspace. Then I noticed the 4" cast iron pipe that was used to be the drain pipe for the house from 1915 through about 2000. The vent for that pipe runs through my attic and straight down to my crawlspace...unused and forgotten. So I cut the pipe and disconnected it from the roof and cut off and closed up any branches it had. I cut it and slapped a screen on it in the crawlspace. In the attic I put on an inline fan (6 watts) and a bit of duct to vaguely direct it around the attic. Early tests say my attic is about 7° cooler. Am I crazy?
I've been working on venting my attic. It's a 1950s build with gable vents and a temperature-controlled fan. That made sense in the pre-ac days to push 130F attic air out, pull 80F house air through a popped attic door, and pull 90F air into the house (or 70+F night air in), I guess, but with retrofitted ac, it's not appropriate.
Nowadays, you want the attic to breathe and hopefully stay ambient. Luckily, the house came with a recent addition of a ridge vent. Unluckily, there's no soffit vents, so the air is still pretty stagnant. I don't use the fan because it's mostly pulling air from the gable vents near the ridge and pulling some from small gaps in the living space ceiling. If you pull from the living space, as others noted with your crawl space, the air must be replaced with outside air, so you have to determine if that's a benefit or a negative. I'm working on adding soffit vents to allow convection currents to flow and give the fan much more outside air availability (along with sealing ceiling openings). While my rafters sit over the wall top plates and provide a 5" gap between them to the soffit eaves , the last installation of batt insulation was rolled up and taped into the rafter bays - just like yours. That's an annoying thing to undo every 16" in hot, dusty, mildewy, rodent-contaminated conditions. I've compromised by cutting the soffit vent openings and poking the insulation with a rod from outside the house. I've wedged some foam rafter baffles in the bays to make sure they stay open, even though they're really meant for blown-in insulation rather than batts. I've used the 16" rectangular individual soffit vents so far, but I'm starting to think I can tackle replacing the soffit panels with vented panels myself while tackling some rotting trim at the same time.
I live where it snows in winter and while this will make the attic cooler, it's supposedly still a benefit to help reduce humidity and circulate air to reduce mustiness. What I know for sure is my gas heat can keep up, my electric ac cannot.
My version of your powered vent is, with a full/sealed basement, I've propped the door with a fan to blow basement air into the living space and hopefully exchange air downwards. That's a relatively close loop, if it worked at all, by exchanging air between two air groups already in near contact via the floor. Agreeing with others, I don't think it should be used for the attic air. But your setup could be a good start to test the effectiveness of the fan and to be a step towards a better solution.
Good luck. Stay cool. Building standards have changed a lot in the last 100 years. I can't wait to find out what common practice today gets ridiculed in 50 years. My bet is on spray-in wall insulation.
I have not studied them enough but my soffits could really use improved venting too. This will probably be my next step. I think poor circulation is why my attic gets so hot. My roof will need replacing in a year or two, I may replace my insulation with spray foam then.
I'm gathering data about the temperature difference in the attic now vs before my crazy pipe vent. I'll post it when I've got a couple of weeks worth.
The roofers may be able to do the vents for a small up charge. I wanted the gutter people to do mine but the gutter price alone was well beyond what my inexperienced DIY ass wanted to pay. I'd recommend adding a ridge vent with the roof though, as that's a very related task.
When I did one corner of the house with soffit vents, I couldn't feel anything in the attic, but I could see cobwebs dancing in the draft above the vents. Nothing in the other corners. So I have to trust they work. I started on the side with the most frequent breeze
Not crazy, but the cool air from the crawlspace has to be replaced, probably by warmer air from outside. So you are cooling the attic but warming the crawlspace. Heat rises. What's the insulation between the crawlspace and house? You may be cooling the attic but warming the house. The attics I know are all vented to/from outside. I would be more inclined to put the cool air from the crawlspace into the house, rather than the attic.
also cool air can not hold as much humidity as warm air. this means that the water (of the warm air in your attic) might condensate in your attic, so stuff might start to get rusty or moldy.
That's interesting! The carrying capacity of air Vs temperature is non-linear so if air in the crawlspace and attic were both near saturated, when mixed the result would probably be super-saturated / condensing.
Hence you get visible condensation from breathing and all sorts of exhausts.
That attic insulation is pretty sad, I doubt there is a vapor barrier or attic and roof venting.
Yes it's sad and old but there's about 8" of it. There's an attic vent in the roof and a vapor barrier in the crawlspace.
That would be my guess, the crawl space is cooler to begin with because there's not enough insulation from the crawlspace and the rest of the house. So the cool air from your crawl space and home is now being sucked into the attic.
Your attic is supposed to be hot, that's why you have so much insulation between your house and the attic, and not the roof and the attic. It's supposed to be closed off from the rest of the climate control.
Old houses were not designed for insulated attics. But, along with attic insulation, the attic and roof needs to be vented, to let the hot air escape. Ideally a ridge vent across the entire roof.
There is a ridge vent
The ridge vent gives the hot air some place to escape that is not your living space. Creating a draft from your living space to your attic is just going to pull your cool air into the attic.
It's from the crawlspace under my house, not a living space at all
Still might be a problem, especially if you don't have great insulation under your subflooring. You're pushing cool air from under your house to the attic. That vacuum of cold air is either going to be replaced by cooler air pulled from your house if you don't have enough insulation, or from the hot air outside.
Pulling in hot air from outside is going to make your AC work harder because that hot air will rise and warm your house. And pulling colder air from your house into the crawl space means your AC is now working harder to cool your house, your crawl space, and your attic.
The space in your attic and your crawlspace are supposed to act as insulated buffer cells between your living space and outside. Connecting the two basically creates a vacuum that vents cool air from the ground to the vent in your roof.
Plus.... Depending on how old your home is, you may unintentionally be pumping a dangerous amount of radon into your attic.
Attic is vented but it does little good without a decent wind. Crawlspace is slightly cooler than outside ambient air, call it 85° in June. The same wind that would help the attic would also remove the cool from the crawlspace I think? Attic is insulated with old old blown fiberglass and then a layer of newer rolled fiberglass - not terrible insulation actually. Also the crawlspace is insulated from the house with spray foam insulation.
Florida man makes risky post to Dull Men's Club.
I salute his courage.
Not crazy but that's your old vent stack for your poo pipe, so let's all pray that the scents soaked into that cast iron is long gone.
You insulated the floor. you should insulate the roof if you want a cool attic. As others said, hot air might condense on cool walls of the crawlspace. I dont aerate my cellar in the summer for that reason.
People do this .... https://youtu.be/26F7X5rjtlM
But this is because many US houses don't have properly insulated and vented attics and roofs. Then people do things like paint their roofs silver.
Sounds good to me as long as the cast iron truly isn't connected to anything. If it's still an active plumbing vent you're fanning sewer gas into your attic. Also it would be a good idea to cap what's left of the pipe where it comes out of the roof so rain doesn't come in.
Agreed. It's capped on the roof but I stuffed it inside the attic too for good measure.
Coincidentally, I saw this yesterday
https://youtu.be/H8-QNBd7MIo?is=J-_EzLKdHj3S_C2u