How can I be sure I am getting the correct the CFM draw from rooms served? - Contractor Talk - Professional Construction and Remodeling Forum

JimmyH · 04-02-2009, 12:24 PM

I have a completed town house project where I need to establish that 2 baths and kitchen are properly vented from a 100 cfm fantech in line exhaust fan.

I should have the 65 cfm required for continuous operation however mirrors continue to fog over and kitchen air is not moved (smokes activate) to our satisfaction.

Arguing with the engineer is no good because the math works, but in practice the system doesn't.

Is there a simple test at 20 - 25 cfm that can be done with minimal expense?

MechAcc · 04-02-2009, 07:49 PM

One thing to remember about venting air out of a structure, air must come in to replace that air. Nature abhors a vacuum. If this is a newer structure and is well sealed it may have trouble bringing in fresh air. A makeup air system may need to be installed or a energy recovery ventilator installed and adjusted to run the building slight positive pressure.

consolidatedbui · 04-03-2009, 02:12 AM

Well i dont think a bath fan is going to fault cause no outside air... Personally, in theory yes, but the house does leak a little..
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use a volumeter????????????

NickTech · 04-03-2009, 07:06 AM

quick smoke test to disprove negative pressure. with the fan off create some smoke(ie cigarette, or use fine talcum powder) ensuring any windows are closed, then energize the fan and observe smoke draw. now repeat process with a window open and observe the draw. note any differences and conclude a solution.
this is now assuming there are no install problems like closed dampers or crushed duct and thee aren't any obstructions outside.
goodluck

flashheatingand · 04-03-2009, 08:52 AM

You checked the ducting and the fan operation? and you aren't getting enough air flow?

Disconnect the intake side of the fan and disconnect the output ducting of the fan, then energize it and do the smoke-test thing. Does it appear to be working ok? Step 2 reset the intake duct and check the airflow (smoke test)is it still ok?. If so, your problem is likely on the output side of the fan.

Before calling out the engineer, I would isolate the components to verify that my stuff is good.

coolmen · 04-09-2009, 07:13 AM

65 cfm for 2 bath and a kitchen does not sound like much if you ask me.

beenthere · 04-12-2009, 08:51 AM

Code generally requires 25CFM per bathroom fan, if they are wired fo continuous 24/7 run.

So that would be 50CFM for 2 bathrooms.

15 CFM for a kithen isn't enough.