Fume Exhauster with air to air heat exchanger incorporating makeup air from outside.

So far I'm thinking a 10 foot long 3" aluminum drier vent pipe with a spiral flow restrictor wrapped around the outside of the 3" tube. That will slip into a 10 foot long piece of PCV pipe that will coaxially carry the outside makeup air into the shop.

Since cold air is denser than hot exhaust airstream the slight loss of duct volume differential should easily provide sufficient outside air.
This system will have over 1100 square inches of heat exchange surface, which should be sufficient to take most of the heat from the exhaust stream.

Anybody got any input?

watch out for condesate, usually the vent is inclined one way or another, try to keep from having sags. tt

Check the University of Saskatchewan . They have done a lot of work on air to air exchangers. :D Also done quite a bit of stuff on energy efficient houses. :D

What are you going to use this for. Your non buildings are just plain too small to warrant such a device? :D

If'n my recall is correct frosting up is a problem with these devices. :D

Now you have had me concentrating all day on this project Franz.

There are two ways to approach this endeavor. The first is a one off for use in your shop. Your Ideas will work well.

Consider having the fresh air terminate in a bucket or some other such contrivance. This will stop the flow of air into the shop if you are not in the exchange mode. It would also catch any condensate. Secondly, attach a cooling fan from a computer [ just the 110 volt fan] or some other very low volume fan to the warm air duct to help exhaust air. This fan gotta be sized to be equal to the outside air coming in and just runs on a manual switch.

Oh-maybe a filter on the incoming air; or should it be on the outgoing air, to avoid pollution of our atmosphere! :D :D

The second approach is commercial and will make you rich.

Using your previous principales convert to a spiral exchanger and package it in a fancy box. Attach a particulate detector for fan operation and have a control panel with some indicator lights that flash for temperature and humidity etc. to make the whole assembly look really top end.

Find a manufacturer and take out TV/newspaper add time and space. Saturate the add availability, take orders, and have your product shipped from the manufacturer to customer. The checks come into your offshore account of course! :D :D

You be a rich man and don't even realize it yet. Every home needs one of these in those cold winter months! :D

Looking at projected heating fuel prices for the winter of 2010-11, and allowing for the presumption we might actually have a damn week or 2 of Summer in 2010 which is doubtful at this point thanks to Mr Gore's Global Warming restriction, it is time to revisit this project.

I figure the point of use fume exhauster made from a computer fan and a couple HVAC fittings which has already proven its ability a few times will be able to carry off all the fumes any single weldor will be able to make in a home shop situation, ought to be able to provide enough pressure to carry those fumes thru an additional 10 or 20 feet of heat exchanger.

Hell, everybody who stayed awake thru 7th grade science knows you can't take air out of a box unless you replace it with incoming air, so the need for makeup air to anyone beyond a car painter is an established fact.

Will heated shop air rising naturally thru the ducting negate need for a larger capacity fan? Will the negative pressure created inthe shop be sufficient to cause outside air to flow into the shop?

Where the hell is Storts when his brilliant mind is needed?

It really depends on how tight the building is. Part of that might have to do with age of construction (older structures being less well sealed), part of it might be more traceable to the buildings designed intent.

You might recall, when I built my shop I intentionally didn't gasket or seal the sill plate/block joint. I have a "U" shaped channel to pass air through when you look at the siding skirting and how the sheetrock hangs half an inch over the block, but it's not at all sealed. The U prevents drafts from outside wind, but doesn't hold pressure at all.

Make up air from such a small fan shouldn't be a concern unless it was new construction with sealed connections at every joint and very tightly fit doors.

Now the ability to pull that much head is an interesting question. Will the fan stall with the burden of that much confined air, or will it still draw sufficient volume as to do the job?

Rather than using a computer fan, I'd go for a small volume (100cfm) bath fan. They get noisier as the restrictions increase, but they have more power and more surface area on the blades so they'd be less susceptible to stalling out. They're also centrifugal blower designs rather than push/pull, so they're more efficient.

Given that the bathroom fan is a gerbyl exercizer, but bear in mind most of the gerbyl cages are reverse incline. That tends to mean sh!t accumulator. Just pull one from a bathroom that's been in use and generally you find them full of dander & dust. That drops efficiency considerably.

I thought your failing to seal the base of the wall was a gesture of friendlyness to the cat's hunting and snack supply.

My cats live with my parents - they wouldn't be allowed in the shop if they were here anyway. Too many sharp chips, so they'd have problems from cleaning their fur.

You've never seen my computer fans have you? :o Talk about dust collectors...



With an appropriate redesign to the housing, you could change the bath fan to a vertical mount and then put a gravity trap before it to prevent the accumulation. We're talking about fume extraction here though, not grinding or machining. Getting bb's all the way to the fan would take some talent, or a fan that had more pull than would be acceptable for anything other than stick or fluxcore.

Thought comes to mind if the area of the inner and outer duct are in the 1/3 ratio and considering outside air would be of a greater density than the heated air in the room, there just might be a venturi effect that could pretty much minimize the fan power necessity.

I don't think you're going to have such luck. If it was going to work like that, you'd need a wood box from Marco to weld inside of - one that seals up tight.

It's a nice thought and good use of applied physics, but just like perpetual motion, you've got other losses to account for in the system.

Aw geez, next thing you're going to get all up on making up the pipe inthe proper direction so vorteces aren't set up at the joynt which will screw up airflow.

A 4" exhaust tube with an extended spiral on the outer diameter inserted into an 8" inlet should provide for maximum heat exchange since the incoming air will be at a slower veloscity than the exhaust air.

Since the snorkasucker inlet will be at bench height, and the incoming makeup air will be about 9 feet up, natural convection should help too, and when the shop heat is on, the inlet pipe will be gaining temperature from the surrounding hot air at the ceiling.

And the arc is at a couple or six thousand degrees above ambient and should cause so much thermal expansion that the exhaust gasses just fly out the snorkel...


It just don't work that way. :P

Yeah, them damn fluid dynamics and friction inside of the pipe system always screw everything up.