-
What is maximum CFM you can get out of a 4 inch B vent? ERV exhaust 65cfm max.
I have a ERV and the installer decided to install the exhaust to an unused 4 inch round B vent that was used for an old unused gas water heater that vents vertical about 100 up to the roof. I can't seem to get more then 65 CFM when I measured it, even though the ERV is rated for 50 - 100CFM (it measures 65- 70 cfm no matter what setting for exhaust). So question is, is that the issue? the 4 inch B vent can't support more then 65 CFM of air flow?
Thanks,
-
-
Surprised your getting that. My chart shows 50 CFM's for 100' 5"
What are you doing concerning condensation in the winter?
-
Thank you for responding. This was just installed a bout a month ago, I didn't even think of condensation, so in the winter the pipe is going to get cold once it gets to the unfinished attic and all that moist 72 degree air is going to be pushed through there and condense and roll down the pipe causing a heck of a problem. Thank you for that, the installer I used took the short cut that was the B vent so here we are. I am going to vent it into the garage that is next wall over and get it off of the B vent..
What is the max CFM of a 35-40 foot run does that make a difference (trying to figure out why its at 65)? I have a 2 story house (3 floors including basement where the b vent starts. So that is probably 40 feet ( 10 feet per floor 4 feet on bottom floor then maybe 10 feet for attic).
Thanks again for pointing out the condensation problem that would have occured, just insane the hvac contractor didn't say gee maybe we shouldn't do that. Guess its pretty obvious now why the ERV isn't working properly since its so out of balance between exhaust and supply air. If exhaust is maxed at 50 - 60CFm and the supply is 2 - 3 times that not much balancing of the air streams there.
-
Do Not vent it into the garage! Possible to positive pressure that room and negative pressure the house. Not a good idea! Might be a code issue also.
Get the contractor back and correct the issue.
How are you measuring the actual CFM's?
-
Thanks for the response I am using a Testo 405i to meaure CFM, set it to 4 inch round duct. Drilled a 1 inch hole in the rigid duct attaching it to the B ducting put it in and measure on average. Said 65-70 CFM no matter the outlet speed I set on the ERV. I also measured where the 4 inch ducting is supplying fresh air just as it enters the hvac return duct just before the filter. I get 80 CFM when ERV is set to 50, and 145 CFM when ERV is set to 100. I guess the ERV is a "roughly" setting not exact? I have a Panasonic Intellibalance 100 ERV.
As far as exhausting ERV into unfinished attached garage, what if I put a vent in the drywall ceiling in the garage? That would eliminate any positive pressure, and negative pressure pushing air into the house through the garage right? And have a side effect of ventilating the garage with exhaust air from the house? You say it may not meet code, when would that ever come up out of curiosity? (an inspector or someone would say you can't do that?)
My only other options are putting in an exhaust vent 6 feet away from the intake vent, but install manual says 10 feet minimum between intake and exhaust? I would have to cut another hole in the front of the house, and go through the brick. No real easy option guys thats why hvac guys took this short cut.
-
I was doing some more research, I did notice I have visible area to the walls on the side of the house but they are like 30 feet away. Could I run a 4 inch pvc pipe to an external wall, cut a whole in the external wall and siding and attach a dryer vent to it, then hook the flex duct to the 4 inch pvc and that could be my exhaust? I don't know what the maximum cfm would be of a 4 inch PVC Pipe 4-in dia 10-ft L Schedule 40 Pipe... I know they use the same kind of pipe to vent my propane furnace?
Thanks again.
-
Where is your installer during all this?
-
As it gets colder outside, the exhaust CFM will increase.
-
Post Likes - 1 Likes, 0 Dislikes