Replacement Air Question

stashia · #1 2007-02-24, 10:39am

I am a little confused still about bringing in replacement air. There is an ac vent directly above my torch which I know is too close but across the hall is a spare bathroom with a small window (the window is in the shower) can I open this for use as replacement air or do I need more flow? I can also open a larger window (30 ft away in the other room/loft) but am concerned about in the summer when it gets really hot having such a large window open. Anyone have a studio set up in your home? How do you do it without cutting holes in the house or having huge ac bills in the summer. Thanks

MikeAurelius · #2 2007-02-24, 2:52pm

No, sorry, you can't use the AC vent.

Replacement air has to come from outside, at least 10 feet from the exhaust duct.

A window is usually good enough, as long as you try to get at least roughly 50 square inches of opening (equates to an 8" round duct).

stashia · #3 2007-02-24, 6:19pm

Thanks -so you think the bathroom window would work? It's the closest one that is more than 10 ft away and is about 23x16(the side that opens)
Sorry for the stupid questions.

MikeAurelius · #4 2007-02-25, 8:15am

Not stupid questions at all.

Dale M. · #5 2007-02-25, 9:36am

If that is all you have, it will work... Just be sure any doors between "studio" and window are open when ventilation is in operation....

Dale

Allie_T · #6 2007-03-02, 2:35am

The distance between my exhaust window and the sliding door I open is 7 feet so am I to assume this is not good enough make up air? I have another window that is about 25 feet away (in the next room). Would that work better? We have now finally moved my studio down to our above ground basement. All the windows and doors are along the same side of the house.... My husband also installed 2 x 475 cfm exhaust fans and put up the ductwork and fed it to where I am torching. Originally, we had gone with the one exhaust but, when I felt the pull, I decided to get another one. The pull now seems to not be great. The pull from the window fans upstairs (when I was 2 storeys up from here) was so great it pulled the flame of the torch. It got annoying, it was so strong. I have used the smoke test and it pulls (and the loo paper test and it pulls) but it just doesn't PULL. I can post photos if necessary. He's sealed all the connections so I am not sure if the fans are just not strong enough or if I am spoiled by the huge pull the window fans had before.

Allie_T · #7 2007-03-02, 2:41am

MikeAurelius · #8 2007-03-02, 5:06am

Ok -- your problem is manyfold --

1) get rid of the flex ducting. You are probably losing better than 50% of your air movement due to turbulence.

2) You are reducing the size of the duct right at the hood (and you hood is nowhere near large enough). This causes severe reduction in airflow. Ducts should never be reduced in size in the direction of the airflow, they should always increase in size if necessary.

3) Adding a 2nd fan on the same line does nothing but cause the two fans to fight each other.

Here's what I'd do:

1) Get rid of that small hood and use a modified kitchen range hood (modified to remove the fan and filters, and opened up on top to allow the mounting of a duct starter ring.

2) Replace all the flex duct with smooth sided galvanized ducting, at least 8" in diameter.

3) Use one fan at the window, properly sized for the hood you are using (100 to 125 CFM per square foot of hood coverage).

The reason your set up worked before is probably because you used a far shorter run of ducting. The flex ducting only gets worse in its air movement capacity the longer it runs.

The open window 25 feet away is fine as long as there is no closed doors inbetween your hood and the open window.

jokersdesign · #9 2007-03-02, 7:01am

Would it be better to set the fan right behind the hood or at the window?

Allie_T · #10 2007-03-02, 7:11am

I appreciate your advice but how can I utilize both exhaust fans? You say they are working against each other, right? Should we have the exhaust fans set up with individual ducting leading to a large vent hood (perhaps with two openings) over the torch?

MikeAurelius · #11 2007-03-03, 8:46am

If you want to use both fans, then you have to use two sets of ducts.

Allie_T · #12 2007-03-03, 11:05pm

I think we're going to sell the fans and get an overhead hood system and then use the solid ductwork. I thought it was going to be adequate but having the exhaust fans so far away loses so much of the suction power. Now, for the overhead systems you have to remove all the filter parts (bar the fans) in the hood, right?

MikeAurelius · #13 2007-03-04, 12:56pm

The only reason you are losing suction power right now is because of the flex ducting you are using. Replace the flex duct and your ventilation will improve.

Yes, if you purchase a kitchen vent hood, you have to remove the filters...but be sure the hood you purchase has the right sized fan on it (100 to 125 CFM per square foot of hood coverage). If it doesn't you are right back where you started from again.

Allie_T · #14 2007-03-20, 10:36pm

DH fixed the exhaust problem this past weekend. He's such a sweetheart