View Full Version : Make up Air and Air Extraction

Michael Ramsey
09-12-2017, 10:54 AM
Good Morning folks, I have been searching the forums all morning seeking an answer to my question. Given the space I have to work with, which is a small 'storage' room in my basement, I will be venting to the outside. I am concerned with creating a negative pressure in my house, it's a pretty tight envelope. I will have a sacrificial basement window in which to run the vent externally. I am wondering if anyone has introduced an intake vent to their laser from the outside air to mitigate conditioned air loss as well as negative pressure. Pics would be awesome if anyone has them.

Kev Williams
09-12-2017, 1:17 PM
Since you're sacrificing a window for air out, use it for air in too..

Doug Fisher
09-12-2017, 1:50 PM
If you don't create a vent in a window or wherever, you will end up sucking air down through your fireplace vent and/or the vent for your gas furnace plus gas water heater (if you have them). Make sure you have a carbon monoxide detector!

Another thing to keep in mind is that if you have the vent and intake mounted in the window you will be sucking in what you are blowing out to some degree unless you take steps to mitigate things. If you aim/route the exhaust upward (since it is heated) and then use a long intake tube like Kev shows to drop down low to suck in air distant from the exhaust, that can help. If you can open a window on the other side of the house/building, that is good too. If you don't have a screen on that window, you can buy an expanding screen insert for the window at Lowe's for less than $10.

Robert Bonenfant
09-12-2017, 4:59 PM
Hey Michael,

We had this exact same issue a few ago - We have Four lasers running in a temperature controlled room in our warehouse - Never though about pulling air back in.
My HVAC made it simple for us, if you moved X amount of air to the outside than you have to replace X amount of air with good air - So if your removing a ton of air with your Laser exhaust you need to find something comparable to pull air back in. For one laser you might be alright with a window but for us we have to add a new air intake into our building to effectively fix the problem. Most of the time You can tell pretty quick if you have a problem, A Head ache will start after a hour or so (Light Oxygen Deprivation), Carbon Dioxide detector can be helpful as well.
Make sure you dont have both air sources in the same place. Send the exhaust to the roof if possible - Dont want that stuff sticking to the side of your house.

Added: The air intake direct into your laser may cause some problems. It really depends what type of laser you have and how your cabinet is setup. If its hot outside and your blow warm air directly into your laser, your gonna have condensation and this will give you a ton of problems. For us a air intake in the room from outside works great and does not affect the rooms temperature that much in the summer - It still stays very cool (Your only running it when the lasers are on). In the winter its perfect because the lasers and chillers generate a good amount of heat and when the cool air comes in, it makes it a very comfortable area to be in. Our intake fans have controlled settings to increase and decrease the speeds (Homedepot sells similar and they are under $300).

Bill George
09-12-2017, 5:43 PM
FYI they do make a air to air heat exchanger. The leaving air warms or colds the incoming. A crafty person could design and build one, not to commercial standards but workable. https://en.wikipedia.org/wiki/Heat_recovery_ventilation

Michael Ramsey
09-13-2017, 10:22 AM
Good morning all~ thanks for the input. I think for simplicity I will just start with a simple in and out vent to start with. I have 2 hopper style basement windows in the space where the laser will be located. I will exhaust out one and allow fresh in the other to eliminate the exhaust being pulled back in. I am mainly working with wood so 99% smoke. I may need to get creative and extend the exhaust a couple feet away from the house though I will need a way to camouflage it somehow. I did see some DIY air to air exchangers and may go down that path in the future if I feel the temperature regulation becomes problematic.

Jerome Stanek
09-13-2017, 2:43 PM
I have made a hood to install on the laser that allows make up air directly into the laser 1 hose goes in and 1 hose goes out that way you won't be cooling or heating the room air.

Michael Ramsey
09-13-2017, 6:00 PM
I have made a hood to install on the laser that allows make up air directly into the laser 1 hose goes in and 1 hose goes out that way you won't be cooling or heating the room air.

That sounds interesting. Do you have a pic of your set up?

John Lifer
09-13-2017, 10:38 PM
Ive got one laser exhausting and a bit home, roughly 3600 sqft. Two chimneys. One upstairs and one connected to stove in basement. It's not used, damper closed but when running for a house or so, i can pull smoke from the main fireplace back down thru stove. Got to open window or door to vent air back in.

Jerome Stanek
09-14-2017, 8:05 AM
I didn't take a picture when I had it in my house now it is my shop and I don't need it anymore