Back in 1956, the builder installed a couple of exhaust fans in this house.
Little fans that vent right into the attic. Not to outdoor air..
One was a bathroom fan and the other was above the kitchen.

We were told venting into the attic could cause all kinds of problems,
but after a few years of not seeing any problems, I replaced the bathroom
fan with a new fan-light fixture combo. (It now uses a newer model w/ CFL).

To keep down the cold-air back-flow, I installed a dryer vent (with it's flap) on the end of the vent hose.
It shuts when the fan is off. I added a small weight to the flap, to keep in from lifting up (and wasting heat)
whenever there was positive pressure in the bath room (door shutting etc).

http://i46.photobucket.com/albums/f1...Solar/z002.jpg



The kitchen fan was another problem. It leaked a lot warm air into the cold attic all winter long.
When the sun hits the roof, the attic peak wall vents (and now the ridge-vent)
exhaust the hot solar air and create a draft, sucking warm kitchen air up into the attic! :mad:
All the little leaks in the house add up.
The draft suction was such, that a 8.5x11 sheet of paper would stick to ceiling vent grill and not fall off!!
The loss in BTUs much have been really high before we got the new replacement windows.

So, we started using a magnetic cover to block the vent input during the winter.
But it was inconvenient taking it down when we needed to vent out the area. (Burnt toast etc).


So, I copied the design of a toilet lid, using a coroplas lid on a plastic bucket. (Removed the bottom of the bucket).
Placed the bucket over the round vent fan(in the attic). The lid flips up when the fan is on.
It drops down when not in use. Extra lid weight (the screw) keeps the drafting down.

The hinge is Gorilla tape and needs replacement every few years.
http://i46.photobucket.com/albums/f1.../Solar/lid.jpg
As you can see, the fan doesn't flip the lid open very wide, when all the doors and windows are closed. (It's cold and wet outdoors today).

I guess we have never seen any moisture problems (in 37 years) with venting into the attic,
because of the attic's peak vents (East side & West side) keep the attic air moving.?.

When we come home to a hot house in the summertime,
that little kitchen fan does a pretty good job of removing hot stale air from the main living area.
At the same time, it's forcing really hot air out of the attic.. :D

Cheers,
Rich

PS:
I can add photos if anyone wants to see them.
Edit: I had a professional cameraman come in and take these marvelous pics! :rolleyes:

I've love to see a picture of this home made flap.

I took some time this weekend to work on this project.

First off, these are the two fans I got from my father in law.
http://ecorenovator.org/pictures/house383.JPG

http://ecorenovator.org/pictures/house385.JPG



The fans run at about 50W each while on.
http://ecorenovator.org/pictures/house384.JPG



I started with the fan attached to the box.
http://ecorenovator.org/pictures/house386.JPG



I removed it from the box and removed the plastic piece. I also removed the motor, took it apart and cleaned it up.
http://ecorenovator.org/pictures/house387.JPG



I found a piece of plywood laying around and cut a notch in it for the water heater exhaust pipe.
http://ecorenovator.org/pictures/house388.JPG



At this point I laid out how I wanted the fans to be oriented on the piece of wood.
http://ecorenovator.org/pictures/house389.JPG



I traced the first fan out on the board.
http://ecorenovator.org/pictures/house390.JPG



Then, I flattened the flanges out on the fan to use for mounting.
http://ecorenovator.org/pictures/house391.JPG



And then I cut a hole for the fan exhaust port.
http://ecorenovator.org/pictures/house392.JPG



I drilled holes in the flange and put some caulk on the bottom to seal the fan to the board.
http://ecorenovator.org/pictures/house393.JPG



With the first one screwed down I moved on to the other fan. I cut the shroud to allow it to sit flat like the other fan.
http://ecorenovator.org/pictures/house394.JPG



Again, I traced and cut a hole in the board.
http://ecorenovator.org/pictures/house395.JPG



I drilled, caulked, and mounted the second fan. I then wired the two fans together.
http://ecorenovator.org/pictures/house396.JPG



So, here we are up in the attic. This is the cutoff chimney. The vent you see is from my water heater. If you look on the upper left corner you can also see that there is a significant step in the brick/morter that will need to be delt with.
http://ecorenovator.org/pictures/house397.JPG



Here is how the piece fits on top of the chimney. Looks pretty good. :)
http://ecorenovator.org/pictures/house398.JPG



So, I just need a way of sealing the board to the chimney. I was thinking just to use great stuff and be done with it, but this is kind of still testing things out and I might need to remove it for tweaks. Does anyone have any ideas?

I'm also going to need some sort of flapper door to prevent heat from going up the chimney. I'm thinking I'll bolt something to the bottom versus having something in the vent hole in the kitchen, but maybe both is a good idea... Anyway, throw out your ideas!

How much air do the fans move when they're running? How do you calculate that the fans are providing more than 100W worth of additional heat to the house, i.e. that you're getting more hot air with the fans running than a 100W heater would provide? I would think that there would be some crossover point where the higher temp of the attic air would offset the power consumption of the fans and you'd want to run the fans only then and above.

The fan motors also produce heat, which will get sucked down the chimney, so it's sort of like adding a small electric heater.

I propose to box in the fans and add a mini-chimney which would suck air from the upper regions of the attic. Add a 180° bend at the end with a flap and filter, and the temp sensor should also be at that height. This set-up should help to keep the fans clean and the noise down.
BTW How noisy are the fans?

http://ecorenovator.org/forum/attach...1&d=1287985384

The fans push a fair amount of air. I have no way of measuring it though.

There will definitely be a crossover point where the fans will not be providing as much heat as they are pushing into the house. I will deal with this via the differential temperature controller. I'll probably start with a difference of 5 degrees F to start with.

Very interesting idea, and I like it! I'll be taking a trip to the home improvement store tonight or tomorrow. I'll see if I can't find something premade that'll make this quicker and easier to put together.

The fans are pretty quiet. I don't anticipate hearing anything except air blowing through the vent when it is on.

For sealing against the chimney, I thinking I'm going to add a 2x4 base/frame to the top of the chimney. The platform (or box if I go that route) will screw onto the 2x4 frame. This will make it easier to remove if need be.

In the mean time. I'll be looking into controller options. I think I have some temperature sensors from when I was doing the arduino thermal differential controller, so I'll probably look into that route first.

I did some quick looking around online. It looks like a .5A bathroom fan will move 100-150 cfm.

OK, that makes sense. So no loss from running the fans.

Daox, are you going to provide an air return to the attic? Or dump the additional air outside like an evaporative cooler?