Important? savings after attic venting ?

[14tokihorn]

The other Post on AC costs got me going...

Curious if anyone has retrofitted their attic venting system, and can comment on how their AC costs declined.

I am eagerly awaiting the roofers to get here next week (hopefully).
- Made a deal with the landlord: that if I did the sweat equity on the soffit venting, then ridge vents would follow, since the roof replacement was going to happen anyway.

There's a plethora of info out there on cost savings, and clearly there are so many factors, that its a chore-and-a-half to do the analysis. So whether you read promo material from the manufacturers or engineering type stuff, they all leave it with 'important' and 'significant' savings.
I did crunch the numbers on balancing the soffits to the published flow of the ridge vents... ended up cutting ~ 48 ft. of soffit and bird block.

So, roughly speaking if you have upgraded to a balanced venting-type system, how did your energy usage benefit - with:

- prog'ble thermostat
- decent attic ventilation (16" blown in over batts)
- AC unit with a middle SEER ratings ?

Thanks

Oh, coming from a gable vent set-up only, which is basically nil.

 

[cinchhorn]

Something to think about, I purchased a new home in May with ridge vents. While I don't doubt the system, my attic is easily 30-40 degrees hotter than the inside of the house. My new ac works extremely hard and I'm installing a vent soon to push that hot air out. If I lived on a hill I would not be complaining, but since I don't, I do complain.

 

[14tokihorn]

^

The dwelling has no method for air intake? ... just ridge vents?
I've heard somewhere that typical AC systems will work like hell in this heat we've had. Any historical data, say monthly- billed Kwatt-hrs. vs. historical temps. will take some work. I can get hist.'l weather data, but I might as well throw out this summers billing ( 40 + days over 100 degrees), and for that matter, last years too (all that rain).

Eh...
My request might be ammended - Comments from anyone who has just retrofitted from an old gable vent only > Soffit and ridge system. the 'balanced' reference was just a ball park gauge to get an idea of how much work was involved... just turned out that way.

 

[brntorng]

It really depends on how much attic insulation you have as to what the pay back period will be. It generally won't amount to a lot of savings since your windows are usually your #1 source of heat gain followed by the ceiling/attic. As far as pay back period, solar screens on sunny windows is hard to beat. If you're already doing a new roof adding a ridge vent doesn't cost much and adding soffit vents doesn't cost much if you do the labor yourself. In that case, it's a reasonable thing to do, especially in an older home that may be lacking attic insulation.

The easiest and cheapest way to lower cooling costs is to turn up the thermostat.

Just noticed the 16" of insulation over batts. That's decent insulation and, therefore, additional attic ventilation will have limited impact.

 

[baboso]

This thread has NCAAroflbox all over it. He is the acknowledged expert on all this stuff.

 

[Scooter]

I"ve seen two kinds of soffet vents. One kind, which I've installed before, is a standard rectangular opening with a small grate put over it -- maybe 8 to 10 feet apart.

the other kind, which sounds easier, are circular and u use a hole saw. But since they are smaller you use more of them.

Can anyone offer insight on comparing these two different types of soffet vents?

 

[14tokihorn]

^
I believe the round ones are suited for installing on the 'bird block'; a.k.a. 'attic block'. that would be a board which is put in the space located where the roof rafters pass over your vertical wall... mine happen to be ~ 1 X 8's. Those round ones I've seen as mavbe 4" in diameter, do they make larger ones?
Of course theres nothing wrong with using them on a bona fide soffit design, like you alluded to, seems like more ladder work to attain the 'net free air' spec.
'Net Free Air' is a designation found on the manu.'rs spec sheet... easy to find on their interweb site, too. (In Sq. inches) Basically, a unobstructed hole would have a NFA rating equal to the linear surface area. then the rating declines depending on such design things such as: louvres (sp), the mesh size of screening they put on (to keep bugs and such out), etc., etc.

edit... you use this rating in the numbers to attain a balanced flow estimation with the out flow method.. ridge / gable vents as an example (converted to linear ft.)

... I need an A/C gratis engineer, not a venting guy.

 

[TheFied]

A buddy of mine is a civil engineer for a firm that specializes in AC design for new buildings.

He told me in importance (his opinion) your best energy savings were:

1) More attic insulation (R30+)
2) Low e windows
3) Ridge cap or ridge vents (whatever they are called)
4) Radiant barrier decking

I was surprised that he had Low emission windows so high but that is how he ranked them for me.

 

[pmg]

I can't help you on the ridge vent/attic/soffit issues. However, I will point out a couple of things. I have a 52 year old house with no attic insulation. (That will be remedied next month). I had to replace my HVAC last month. I went from a 9 SEER to a 17 SEER. I don't have quite enough info for an apples to apples comparison, but I have been closely monitoring my kwh usage and it looks like it is using about 40% of what the previous unit was using. Also, I have a spreadsheet with the last 2+ years of "Cooling Degree Days" data; this is much more significant for comparing than basic weather data. (I used Heating Deg days for heating usage.)

And, yes, 2007 is not a good year to use for comparison as it was so mild.

I have been pleasantly surprised by the energy efficiency improvements, and can hardly wait for my insulation to see what happens then.

Also,solar screens should help a lot in the winter with heating, when your trees have no leaves and your windows face the sky.

 

[Luke Duke]

I just had a 16 SEER and a 95% efficient furnace installed last week. This should be a big improvement from the 27 year old AC/furnace that it replaced.

 

[Summerof79]

YES- soffit vents will make a difference because your insulation is battling the heat differntial. I speak from first hand knowledge here. While it may be 100 degrees outside it's 130 lets say in the attic. Simple thermal dynamics will cause the 100 degree air to be drawn in to displace the 130 degree (possibly hotter) air in your attic. Your insulation is MUCH better at 110 than say 140.

Super ******* chap to install for decent savings. The grids are probably les than $5. make a template out of cardboard 1-1/2 inches inside the size of the grid and mark out your cuts. FIGURE OUT WHERE THE TRUSSES ARE. That way you don't find that you are running into a 2 x 6 mid way through a vent. You can usually tell by the staples/nails where the tursses are.

use a whole saw to start TWO corners and then use a sawzall to zip through the cuts. Then a magnetic bit sleeve( don;t know what it's really called) that will hold TINY 3/8 screws to secure the vents in place.

 

[Scooter]

thanks, summer, that was very helpful.