Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 08-29-2012, 05:22 PM   #1
Member
 
Join Date: Aug 2012
Posts: 44
Rewards Points: 25
Default

Ashrae 62.2 Mechanical Ventilation


I am having air sealing and new layer of cellulose in the attic to hopefully lower winter attic temp and cut down on ice dams (currently attic gets stuck at 40 degrees even if outside temp is 5 degrees).

They are going to run a blower door test but because my house is "new" (2004) and "tight" they predict I might need "mechanical ventilation" to ensure enough CFM replacement airflow at all times.

I've read the options and am thinking that just leaving one of my many bathroom exhaust fans on 24/7 would satisfy Ashrae 62.2.

I have some questions for you

1) Any ideas on best way to "hard wire" the fan so it stays on? Do I NEED to do this? Or can I just tape the switch or put on a little sticker that says LEAVE ON or whatever. Is Ashrae a "code" issue or is it a "recommendation"?? (i.e. if you don't "qualify" under the guidelines by hard-wiring the fan, what happens in reality?)

2) Currently all 4 of my bathroom fans exhaust up into the attic and their pipes just terminate at the soffit (not to a real soffit vent but the pipe just stops at the top of the soffit). The contractor is telling me I "must" fix this and I do understand why, but I'd prefer they don't poke 4 more holes in my roof so that I now have 4 more chances of roof leak. I see that one can buy soffit exhaust vents....can't I just use those? I understand the principle that the soffits are intaking air, but I think in the real world if you locate an exhaust vent 3+ feet away, it's not as if all the "moist air" is going to just fly right over and back up into the soffit without mixing with a lot of normal outside air first....

Alternatively, is it OK to just route the bathroom exhaust pipe up and right in front of one of the roof mushroom vents? From there it could just make its way on out of the house.

I have no signs of mold, water drips or any "moisture problem" for the past 8 years while my bathroom vents have been "wrong" so I want to do the right thing but also not be silly about poking holes in the roof needlessly, especially since most of the fans are near the outside walls and therefore their exhausts would be very low on the roof......

Hogan773 is offline   Reply With Quote
Old 08-29-2012, 07:16 PM   #2
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,015
Rewards Points: 3,696
Default

Ashrae 62.2 Mechanical Ventilation


Once your attic temp drops, you will get condensation in the attic from those bathroom vents.

How big is your house, and how many bedrooms does it have.

Does your range hood vent outside?

beenthere is online now   Reply With Quote
Old 08-29-2012, 10:00 PM   #3
Member
 
Join Date: Aug 2012
Posts: 44
Rewards Points: 25
Default

Ashrae 62.2 Mechanical Ventilation


Quote:
Originally Posted by beenthere View Post
Once your attic temp drops, you will get condensation in the attic from those bathroom vents.

How big is your house, and how many bedrooms does it have.

Does your range hood vent outside?

3000 sqft house, 4 bedrooms all on upper floor. 3 bath fans upstairs pls another on first floor that also appears to run all the way up into the attic.

Reality is only 2 of the 4 ever get used much. I was thinking of leaving the 1 fan on which is right in the middle of the upstairs, open to the center of the house, as my "mechanical ventilation" fan if I need it.

I have a range hood that does vent straight outside....there is a little flapper in the brick wall right behind the range.....can really blow hard on the HIGH setting.

I'd think when my attic is sitting at 40 degrees all winter that it would still be enough to cause condensation if there was enough moisture coming from bath fans....also my attic floor is pretty leaky with all the can lights, hence why it couldn't get below 40 degrees and hence why I am having the sealing and insulation. So I would have thought the moisture coming up that way would have shown itself in condensation over the past 8 years.

I just have trouble believing that all newly built houses today run ALL THEIR BATH FANS up through the roof !?!? But maybe they do.
Hogan773 is offline   Reply With Quote
Old 08-29-2012, 10:52 PM   #4
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,015
Rewards Points: 3,696
Default

Ashrae 62.2 Mechanical Ventilation


Yes, there vents are ran outside, some through the roof, others through the sofit, some through gables.

Once you seal the attic, you'll need a way for fresh air to get in, or your exhaust fans won't be exhausting much.

Your homes size and number of bedrooms would require 68CFM of constant fresh air, or an intermittent 136 CFM for 15 minutes twice and hour.
beenthere is online now   Reply With Quote
Old 08-30-2012, 10:52 AM   #5
Member
 
Join Date: Aug 2012
Posts: 44
Rewards Points: 25
Default

Ashrae 62.2 Mechanical Ventilation


Quote:
Originally Posted by beenthere View Post
Yes, there vents are ran outside, some through the roof, others through the sofit, some through gables.

Once you seal the attic, you'll need a way for fresh air to get in, or your exhaust fans won't be exhausting much.

Your homes size and number of bedrooms would require 68CFM of constant fresh air, or an intermittent 136 CFM for 15 minutes twice and hour.
Yep I came to the same number....I've been just using 70 cfm in my head.

I assumed that there will still be enough cracks, under doors, etc for air to come in. 70 cfm didn't seem like a huge amount. Actually I have two "open" PVC pipes on top of my Powervent hot water heaters in the basement that are effectively open to the outside (they aren't sealed down to the top of the powervent), so unless the powervent is actually running, that is a surefire way for air to get sucked into the house as a worst case if there aren't enough other cracks on the first or second floor. I'd think the powervents are plenty strong enough to overcome any "negative pressure" created by a bath fan (mine are each 80 cfm rated). Probably a decent chance that my 80 cfms are really only pulling 60 or so depending on the run of exhaust pipe, but that's probably close enough given that we are generally opening doors, using the other bath fans intermittently, etc.
Hogan773 is offline   Reply With Quote
Old 08-30-2012, 06:23 PM   #6
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,015
Rewards Points: 3,696
Default

Ashrae 62.2 Mechanical Ventilation


If you have a blower door test done, and it says you need to bring in fresh air. then the cracks you talk about, aren't enough.
beenthere is online now   Reply With Quote
Old 08-31-2012, 12:31 AM   #7
Member
 
Join Date: Aug 2012
Posts: 44
Rewards Points: 25
Default

Ashrae 62.2 Mechanical Ventilation


Quote:
Originally Posted by beenthere View Post
If you have a blower door test done, and it says you need to bring in fresh air. then the cracks you talk about, aren't enough.

Ok we'll see after they do the blower door. I thought the point of the fan was to pull some air in while it otherwise wouldnt come in (enough).

What about my question on hardwiring the bath fan? Is that something that is required in reality under Ashrae?
Hogan773 is offline   Reply With Quote
Old 08-31-2012, 05:25 AM   #8
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,015
Rewards Points: 3,696
Default

Ashrae 62.2 Mechanical Ventilation


Hard wiring bath fan is not required, and wouldn't work well. Since the bathroom door would need to be open 24/7.

Mechanical fresh air, pushes air into the house, so its not under a negative pressure.
beenthere is online now   Reply With Quote
Old 08-31-2012, 10:37 AM   #9
Member
 
Join Date: Aug 2012
Posts: 44
Rewards Points: 25
Default

Ashrae 62.2 Mechanical Ventilation


Quote:
Originally Posted by beenthere View Post
Hard wiring bath fan is not required, and wouldn't work well. Since the bathroom door would need to be open 24/7.

Mechanical fresh air, pushes air into the house, so its not under a negative pressure.
There are several options for mechanical ventilation and not all of them push air into the house. The more common are actually exhaust options. There are also balanced options with both intake and exhaust, and some options that just tap a feed into the return air on your HVAC system.

It seems that you may choose depending on climate. Intake systems aren't best for colder climates because you're pushing warm moist interior air out through cracks and into the walls, where it can condense and cause mold issues. The reverse is true for hot humid climates where you are pulling in hot air through cracks etc where it may condense.

Perhaps including an intake vent is a good idea if it allows the air to enter more easily than through all the cracks, as you said.
Hogan773 is offline   Reply With Quote
Old 08-31-2012, 06:16 PM   #10
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,015
Rewards Points: 3,696
Default

Ashrae 62.2 Mechanical Ventilation


ERVs/HRVs are generally the best for fresh air. However they aren't great at providing make up air for range exhaust hoods.

Fresh air intakes that are tapped into the return duct pressurize the house.

Condensation is possible in the winter. but doesn't happen as easily as some make it out to happen.

beenthere is online now   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Garage ceiling insulation MNHouseRepair Insulation 16 12-05-2011 03:57 PM
Ventilation - Opposing gable, limited soffit + box vents = Screwed up? darlingm Roofing/Siding 1 09-07-2011 11:13 AM
Need HELP swapping a Vision pro 8320u1008 to an IAQ one N01B4ME HVAC 161 01-10-2011 03:30 PM
Honeywell Visionpro IAQ function 406 ventilation in high humidity ? Charlie123 HVAC 1 05-08-2010 12:19 PM
Light, Ventilation, and Heating code requirements sarbear HVAC 12 11-30-2009 12:10 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.