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Old 07-01-2010, 12:29 PM   #1
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proper intake vents for ridge vent??


hey everyone! i am in the process of installing a ridge vent on my home and need advice, or a second opinion on what ive done here. ok, first of all, there was no intake vents anywhere around my house, so i decided to drill 2 inch holes on the blocking between the rafters for vents. after i had drilled holes i realized the insulation might restrict the airflow so "my fix" whas to slide and glue some 12 inch pieces of pvc pipe to bypass the insulation. my question is how do i figure out if the intake holes are sufficient for the size attic i have? will this work?? there are 145 vent holes i drilled and the attic space is 1500.00sq ft. my ridge vent will be the hole span of the ridge which is about 75 ft long. any help appreciated



Last edited by arty007; 07-01-2010 at 12:56 PM. Reason: adding pics
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Old 07-01-2010, 05:43 PM   #2
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proper intake vents for ridge vent??


Well, that's fairly ingenious. You need a minimum of one sq ft of free vent per 300 ft sq of attic divided equally between intake and outlet. So, at 1500 sq ft, you need 5 sq ft of vent.

You have a little over 3 sq ft of inlet if my calculations are correct.

Assuming 9 sq in per foot of ridge vent, you have about 4.6 sq ft of outlet.

So, it could be balanced a little better, but you're above the minimum.

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Old 07-01-2010, 06:08 PM   #3
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proper intake vents for ridge vent??


thanks!
"correction on the actual ridge vent length", its actually 57 ft of ridge vent that ill be using the rest im going to cancell out because i have cathedral ceilings on the living room and dining room. what other thing can i do to better balance this out?? i was going to cut 2 or 3 inches of the top of the blocking off and slide in some baffles but i couldnt find none here in california. most roofing places didnt even know what i was talking about.
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Old 07-05-2010, 01:25 AM   #4
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proper intake vents for ridge vent??


My calculations are quite different...... 145 holes at 2" (3.14) = 455sq.in./144 = 3.16sq.ft. total soffit intake venting.

75' ridge at 18sq.in.per ft. = 1350sq.in./144 = 9.38sq.ft. total exhaust, almost three times more.......

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Old 07-05-2010, 02:32 AM   #5
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proper intake vents for ridge vent??


Quote:
Originally Posted by GBR in WA View Post
My calculations are quite different...... 145 holes at 2" (3.14) = 455sq.in./144 = 3.16sq.ft. total soffit intake venting.

75' ridge at 18sq.in.per ft. = 1350sq.in./144 = 9.38sq.ft. total exhaust, almost three times more.......

Be safe, Gary
what happens in this situation? since he's just above minimum in intake does the extra exhaust just not matter? kind of like cylinder heads where you can do all the work you want to the exhaust port but unless the intakes come up as well, there's no more power

it seems like 3.16sq ft of intake and 3.16 sq ft on exhaust wouldn't be wildly different than 9.38 sq ft of exhaust, does velocity slow with that much on the exhaust side or?
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Old 07-05-2010, 09:59 AM   #6
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proper intake vents for ridge vent??


it is actualy 57 ft of ridge vent, still seems like im under balanced tho.
i might cut off three inches off the top of the blocking with a sawsawl in a couple of places to help with the intake,(3x 14 inches) but yeah i too would like to know how would leaving it like this affect the overral performance of the ridge vent? i have a 1500 sq ft of attic space and dont think i need the whole 57 ft of ridge vent can i cut off (plywood sheeting)only the lenght required for this attic? i am puttingthe whole lenght of ridge vent for astetic purposes only. thanks for the help!

btw... im installing a ridge vent from airvent (shingle vent 2a 7 inch version)16 sq inches of net free area per linear foot.
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Old 07-05-2010, 02:40 PM   #7
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proper intake vents for ridge vent??


Page #615, Soffit vents- third paragraph---balanced: http://books.google.com/books?id=Z8a...lation&f=false

Be safe, Gary
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Old 07-06-2010, 01:34 AM   #8
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proper intake vents for ridge vent??


read that, trying to visualize this whole thing. as heat rises it pulls on the sofit vent creating that chimney effect. if you limit intake flow in comparison to exhaust it seems like you would if anything be creating more suction at the sofit. i can't visualize reversal on excessive exhaust but it's real easy to visualize on excessive intake
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Old 07-06-2010, 08:06 PM   #9
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proper intake vents for ridge vent??


The PVC pipes through the insulation is pretty ingenious. Is there any advantage to closing that in with a soffit and adding the vents to the underside of the soffit, or is that strictly cosmetic?

Last edited by Jim F; 07-06-2010 at 08:12 PM.
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Old 07-06-2010, 09:48 PM   #10
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proper intake vents for ridge vent??


Well arty007, I just realized you have a lot less than I first figured. 3.14" was for a 2" hole-- net clear. With the PVC, it's reduced another 3/16 on the diameter for the pipe thickness to 2" NFVA. Then deduct for the screening--- screen-door- 50% open and closed = 1" NFVA, which puts you far below minimum. Someone check that.....

Then if any bad weather, the location will put water into the attic as it's next to the house in the positive air pressure area rather than next to the fascia in the negative air pressure. Page 605----- 1-7 rules ----in my sited previously.

The tubes will only reduce the NFVA and leave dead air spots between/behind them where heated air from below could make ice dams above, if in a colder location. Ideally would want wind-blockers or similar the stop wind-washing of the insulation: http://www.adoproducts.com/wind.html

The best way would be with rigid foam board over the plate line: http://www.homeenergy.org/archive/he...96/961110.html

With 16 NFVA for an exhaust, that helps a little. Then there is the variable of the cathedral section and only two holes in some bays…….

” hardware cloth is better NFVA. If you joined the holes as mentioned, add rigid foam board on top of the insulation to create a 1-1/2” air space deep chute for 2’ away. 2- 11” pieces side by side may work. You could even find the electrical wires at the outside wall from the joined holes to can foam them to air seal: http://www.rd.com/how-to-seal-attic-...icle18158.html At least at the cathedral section.

Be safe, Gary
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Old 07-07-2010, 01:35 AM   #11
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proper intake vents for ridge vent??







this is what my roof looks like more or less
thanks for all your help! ive learned alot these couple of days and if i knew where to get those baffles earlier i would have jumped on them
hate to take them all off now i might just add a few baffles to help with the intake. what you think? how many would i need to be on the safe side and have adequate intake? does leaving the cathedral side of the ridge as is (without cutting opening)and just installing the ridge vent over the sheating affect the exhaust at all? sorry for all the questions but this aint really my cup of tea!
btw, im in california "los angeles" area to be exact, so no ice, or snow in these parts of town.

Last edited by arty007; 07-07-2010 at 01:46 AM.
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Old 07-29-2010, 09:34 AM   #12
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proper intake vents for ridge vent??


hey guys i have been busy doing other things that had to put my project on hold for a bit. i also realize that the intake vents i installed are not enough, as a matter of fact, my attic space is 1500sq ft which according to my math i would only need about 25 lineal feet of attic ridge vent I cut out 52 ft of attic ridge!double what was needed for my attic space according to airvent.so i now need (double the intake vent) or do I??I have been trying to figure out how many intake openings 4inch by 14 inch i will need to have an equal amount of venting can someone help me figure this out im spinning my wheels here. thanks!
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Old 07-30-2010, 11:16 PM   #13
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proper intake vents for ridge vent??


http://www.lomanco.com/ProductPAGES/cseries.html

This will get you started. I will be back..... Brain tired.

Be safe, Gary
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Old 07-31-2010, 09:56 AM   #14
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proper intake vents for ridge vent??


i was looking at them, but wonder why do they come in 16 inch when between the rafters the actual dimention is 14 1/2 or so? ill be monitoring later thx.
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Old 07-31-2010, 12:28 PM   #15
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proper intake vents for ridge vent??


Need 3/4" on each end for material stiffness and nailing flange to get maximum opening out to the 14-1/2".

Be safe, Gary

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