Venting out of a chimney?

Charli! · #1 2012-10-22, 12:09pm

I finally have a house with a spare room that will one day become my craft room! As an old victorian property every single room has a chimney. The chimneys are unused, but not blocked and in good shape (so the chimney sweep says). The area where I would like my work bench is in front of said chimney, would it be possible to vent the exhaust from my torch out the chimney? Or would I need the worlds biggest fan to actually make exhaust go out of the chimney stack? Any other problems that you can foresee?

My other option being to make a hole in each side of the chimney and pipe the exhaust gases through some pipe to the outside that way.

Alaska · #2 2012-10-22, 1:05pm

Quote:

Originally Posted by Charli!

Or would I need the worlds biggest fan to actually make exhaust go out of the chimney stack?

Fan size is dependent on the area that is being exhausted in your work area. i.e. a whole room or a Baily box enclosure, etc. In addition, the amount of back pressure (SP) due to diameter of duct, number or turns and length will also factor into the equation.

A 1000 CFM fan at 0 SP will not produce 1000 CFM at .5 SP. A shorter exhaust path, in general, will result in less back pressure which can result in the need for a fan with a smaller CFM rating.

Also keep in mind the need for a supply of fresh make up air that is located at least 10 feet away from your outside exhaust.

houptdavid · #3 2012-10-22, 2:20pm

If I recall if it is an unlined chimney the answer is NO!

squid · #4 2012-10-22, 2:31pm

Quote:

Originally Posted by houptdavid

If I recall if it is an unlined chimney the answer is NO!

Wouldn't it work if you ran the duct all the way to the top?

houptdavid · #5 2012-10-22, 4:09pm

Quote:

Originally Posted by squid

Wouldn't it work if you ran the duct all the way to the top?

Yes, If I remember it has something to do with the exhaust eating the mortar between the bricks.

and then there is the possibility of back draft down one of the other flues

laserglass · #6 2012-10-23, 4:45am

NO...do not vent out of a chimney!!!!!!!

Charli! · #7 2012-10-23, 3:12pm

Quote:

Originally Posted by laserglass

NO...do not vent out of a chimney!!!!!!!

Ok.. but why? Just cos I'm nosey, you see. And I'm thinking if I shouldn't use the chimney then is this because vents shouldn't run upwards? Plan 2 was to make the vent go upwards next to the chimney and vent air out of the roof (in a place where rain wouldn't come in, obviously).

The chimney is unlined, but apparently usable in its current state (as in the chimney sweep person came out, cleared it, and tested it with smoke tablets to say that it doesn't need lining if I were to use it for a wood burning stove).

Alaska · #8 2012-10-23, 6:36pm

Your best bet is to ask a local heating/ventilation contractor as they are aware of local rules and city codes that would apply to your needs.

Charli! · #9 2012-10-24, 1:37am

Quote:

Originally Posted by Alaska

Your best bet is to ask a local heating/ventilation contractor as they are aware of local rules and city codes that would apply to your needs.

Yeah I am struggling with that.. of the six companies I have asked 5 of them won't even speak to me as they don't do small domestic installations, and the last one just shrugged at me and said he didn't know. The builder was the most useful actually, but he doesn't really have an understanding of what lampwork is or what I'm trying to do.. he was the one that suggested using the chimney.

I shall probably stop trying to build things in in a permanent fashion and just do what I do now- put a board in the window with a hole through it that the vent runs through.

laserglass · #10 2012-10-24, 5:29am

Quote:

Originally Posted by Charli!

Ok.. but why? Just cos I'm nosey, you see. And I'm thinking if I shouldn't use the chimney then is this because vents shouldn't run upwards? Plan 2 was to make the vent go upwards next to the chimney and vent air out of the roof (in a place where rain wouldn't come in, obviously).

The chimney is unlined, but apparently usable in its current state (as in the chimney sweep person came out, cleared it, and tested it with smoke tablets to say that it doesn't need lining if I were to use it for a wood burning stove).

all ventilation fans have difficulty with moving gases against a large head (duct resistance or back pressure). for that reason, vent ducts should be as large as possible, as short as possible, and have minimal turns. a vent tube run up through the center of a chimney would have a large head to resist ventilation so even though you buy a high CFM fan, you do not get very much gas movement.

chimneys work because the wood stove, or heater has a high temperature to set up natural circulation because the hot gases are lighter than air and drift up. but the temperature from a ventilation hood is much much lower. even though the flame on your torch is hot, the heat from it gets diluted by all of the room temperature air that also gets ventilated so that the average temperature of the ventilation duct is not too much different that room temperature.

drill a hole through a wall, or make an insert through a window so that you can vent directly outside with a minimal length of the duct.

Charli! · #11 2012-10-24, 9:51am

Thanks Mark for your fantastic explanation

houptdavid · #12 2012-10-24, 10:11am

Quote:

Originally Posted by Charli!

and the last one just shrugged at me and said he didn't know. The builder was the most useful actually, but he doesn't really have an understanding of what lampwork is or what I'm trying to do.. he was the one that suggested using the chimney.

I shall probably stop trying to build things in in a permanent fashion and just do what I do now- put a board in the window with a hole through it that the vent runs through.

It is no different than installing a range hood, I don't get what they find so hard to understand.
Simply go straight out the wall.

Alaska · #13 2012-10-24, 1:49pm

Quote:

Originally Posted by Charli!

Yeah I am struggling with that.. of the six companies I have asked 5 of them won't even speak to me as they don't do small domestic installations, and the last one just shrugged at me and said he didn't know.

Another source may be your local building codes inspector or office. Often they can advise you as to what is within local code.

Some installations require a permit and city inspection. While other modifications made by the home owner do not require either a permit or inspection.