replace passive roof vents?

[slakwhere]

so the garage has been sweltering all summer, so i spoke with an architect buddy of mine who suggested the following

1) replace passive roof vents with active (fan) system (or possibly a gable vent)

2) insulate

i have 2 passive vents in the north side of the roof, i am wondering what it would take to install an active fan vent in it's place? do they make a drop in kit? would a gable vent or 2 be as effective as the roof vents?

 

[Charles (in GA)]

Guys at work have power vents in their roof. The do not hold up well at all, and seem to fail every couple of years. I would opt for a gable vent fan, or a whole house (attic) fan which is slow turning and moves lots of air.

Charles

 

[slakwhere]

Guys at work have power vents in their roof. The do not hold up well at all, and seem to fail every couple of years. I would opt for a gable vent fan, or a whole house (attic) fan which is slow turning and moves lots of air.

Charles

if nothing else it should be easier to install/replace and a little bit cheaper.

any suggestions on the following configurations?

1 push 1 pull (cross-ventilate)
2 pulling air in (vented through existing passive at top/soffits for exit)
2 pushing air out (venting air in through existing passive)

 

[nwav8tor]

Not an expert but here's my .02:

You don't specify your location. Are you worried only about cooling, or will winter heating also be a factor?

Insulation is (in my mind) the biggest step in keeping the garage cool, but you need to keep the attic above the insulation from keeping the hot air trapped. Passive roof vents or gable vents are exit avenues for the attic air. You need good soffit vents for air intake. If you've got good soffit vents for intake (or can add more) then a power ventilator might improve the air flow over static vents. Some experts say the powered systems pull too much air from the living spaces through cracks/leaks but that shouldn't be too bad for over the garage. If installed with the gable vent I'd put it as an exaust blower configuration drawing air ftrom the soffit vents and exiting through the gable vent.

I installed a COSTCO solar powered vent in the attic above my house last fall. It simply rplaced one of the existing passive roof vents. The instructions said to block off all the other passive vents so the solar fan would **** outside air only through the soffit vents and exhaust through the single fan vent. It's temperature controlled in the summer and humidity controlled in the winter. Had it for over a year so far without any problems.

For my garage project, I'm just going with passive ventilation. I'm adding 2 more roof vents to the 2 existing over my 3-1/2 car garage and doubling the soffit vents to insure adequate airflow both summer and winter. Once that's done and my lighing, electrical wiring and roof heater are installed' I'll blow-in insulation in both the ceiling and walls to better control the environment.

Putting in a whole house fan just for the garage might be a bit of overkill, but should work for cooling in the hot season, not sure what it'd do for you if you have cold winters...

Paul

 

[Toymeister]

Guys at work have power vents in their roof. The do not hold up well at all, and seem to fail every couple of years. I would opt for a gable vent fan, or a whole house (attic) fan which is slow turning and moves lots of air.

Charles

I agree and disagree. There are three grades of fan motors. The big box stores sell the cheapest. These are the ones Charles coworkers have. You can tell by the amperage 3.1 amps. Next are the capacitor start ones they draw about 1.5 amps and move more air than the cheapies try this one http://www.amazon.com/dp/B0081ZUWX6/?tag=atomicindus08-20 the final grade are the DC fans with brushes. These will last 20+ years but oh will they cost you. I paid 300.00 for a US made one but it is 12' high in the attic so I am fine with the cost.

Finally there are solar fans. They sound great, the problem is the CFM ratings are pure fiction and they work when you don't need them to. THe attic remains very hot until the early evening and you don't need the fan to run in the winter, so if you go this route at least add a switch and shut it off seasonally.

 

[Falcon67]

Gable probably works the best As fans go - but it'll have to be all gable (both ends) and no deck vents. The $100 unit I bought has a decent thermostat at least. Insulate is way better. My shop stays easy 10~15 F cooler than outside 30~40 cooler than the reflective roof deck. With only passive vents.

 

[Treeman]

Nobody can answer this question unless all the details are know.

The general location in the country (north vs. south) and the building design/construction are needed.

As far as we know, he might have open trusses with no ceiling, as in a pole building.

Keeping in mind the simple principle that hot air rises is the first step. Th OP's ideas about pushing/pulling fans does not make any sense, unless he is considering the whole house fan idea.

 

[slakwhere]

Nobody can answer this question unless all the details are know.

The general location in the country (north vs. south) and the building design/construction are needed.

As far as we know, he might have open trusses with no ceiling, as in a pole building.

Keeping in mind the simple principle that hot air rises is the first step. Th OP's ideas about pushing/pulling fans does not make any sense, unless he is considering the whole house fan idea.

i'm in salt lake city, so 90+ in the summer and below freezing in the winter. 24 x 29 garage with an attic. drywall on all 4 walls & ceiling but no insulation. 2 passive vents in the north side of the roof, 2 decorative gabels (1 west, 1 east) but they don't actually let air in so i'd need to cut them open.

Insulation is definitely going to happen, but if i can help with gable fans or active vents i'm down to do that first (before i have to deal with working in all the blown in insulation).

 

[Falcon67]

Just to clarify - if you open those gables and put in a gable fan, the gable fans are designed to pull air out of the attic and exhaust it outside. You will need to seal up the existing roof vents because if you don't the fan will pull from the closest one and you'll get almost zero benefit out of the gable exhaust fan.

Note if you are going to rework the gables and wire in a fan, it'd be a little easier to do that before insulation. However, you will get immediate use of the insulation, so your pick. I have only R13 in the attic but the little 10K BTU AC unit can keep 672 sq/ft at 80~82.

 

[csp]

Regardless of what system you use be sure that you have as much intake air as exhaust air. A fan is no good if fresh cooler air isn't being pulled in as hot air is being exhausted.

 

[slakwhere]

thanks guys. sounds like i may try to seal the roof vents and point the gable fans to exhaust. then insulate after all the other work in the garage is done.

 

[BadgerBoilerMN]

Powered attic vents are generally a waste of time, money and continue to burn both fuel and maintenance dollars. A well ventilated attic space is the key and accepted practice for some time now.

http://www.nrca.net/consumer/attic_ventilation/passive.aspx

 

[Highbeam]

If it can be done effectively without power then why would you want to use power vents? When the fan motor fails, your attic will become a super hot place since you sealed up the normal ventilation. This could damage the roofing and the stale air up there could cause mold. The fans are noisy, cost money to run, money to buy, and seem to only be a band-aid for improper ventilation design.

You are in blazing hot Utah with no insulation and your barn is hot. Did you insulate before the walls were sheetrocked?

Insulation and natural ventilation is my vote.

 

[1967marti]

I put in one of the solar powered fans in my house attic. It runs as long as there is sun on the solar cells. Its been running every day for over a year now with no issues... Only down-side so far is that it was a litle over 200$ from HD.

 

[Toymeister]

Powered attic vents are generally a waste of time, money and continue to burn both fuel and maintenance dollars. A well ventilated attic space is the key and accepted practice for some time now.

It true that passive is the most common and it always works but it is not the best in many homes. Lets take your attic and lets say you are Michigan with a 4/12 roof then chances are you're covered with your6' high attic, now take my attic in the south with a 12/12 roof where the peak is 14 feet high in the attic. Not only is it hotter than the north but I have much more volume accumulating heat that needs to be vented. The builder used passive as it is cheaper but it is not the best.

 

[Highbeam]

It's not the volume of that huge attic that is your problem, it is the larger surface area of the roof that can catch more sun and heat the attic space with more btus that need to be dumped to pervent high attic temps. You need more ventilation than a shop with flatter roof but only slightly. Certainly within the range of passive ventilation. It is very easy to meet the minimum ventilation requirements for even a 12/12 roof.

 

[Falcon67]

Our house has a 6/12 pitch with no gables - all hips and valleys. The builder didn't put in ANY passive vents on the roof, only eve vents. I put 4 up on top last spring after we got settled in the house. When I cut the first 9" hole up near the ridge, the air coming out liked to knocked me off the roof. And the air was like a blast furnace. Adding the passive up top knocked about 20F out of the attic temps. The calculators say I need 9 vents up there to balance the eve vents LOL - no way, no space for 'em. I'm putting in one more to bleed air off a low to high transition over a bedroom and that's it.

 

[Highbeam]

The codes should give a number of sqaure inches or square feet of ventilation area. You don't need to use 9 of anything, you could use one really big vent instead. Think cupola. Your attic is a big chimney.

 

[kartracer23]

I put in one of the solar powered fans in my house attic. It runs as long as there is sun on the solar cells. Its been running every day for over a year now with no issues... Only down-side so far is that it was a litle over 200$ from HD.

Just put one of those on my new garage (hip roof). It's detached and not heated or cooled so I just wanted something to vent the worst of the heat off. And being a hip, nothing gets trapped in there anyway - when it's not running it's just a big chimney right near the peak. I don't know that I'd put one on a house though. It takes pretty much direct sun to get it to turn. What's really needed is either a battery storage system or a hybrid solar / electric version to make them as good as their electric counterparts.

 

[Falcon67]

The codes should give a number of sqaure inches or square feet of ventilation area. You don't need to use 9 of anything, you could use one really big vent instead. Think cupola. Your attic is a big chimney.

LOL, good point - I would need 9 of the type of vent I put on the roof. I'm ignoring the codes. It's a multi-hip roof with all kinds of angles, no place for a cupola and it would look terribly out of place. Working well enough as is. The codes typically ask for 50% up and 50% lower, which is how the shop is done.

 

[Slimgene]

With an ceiling area of 24 x 29 that's ~700 sq ft of heat coming through. Your best value will come from insulating above the ceiling with about R-30. This will reduce your shop temperature significantly. Passive vents in the gables might be enough.

Insulating at a minimum, your west facing wall will also help.

 

[nwav8tor]

In my research, I found these important points to remember:

1) Provide 1" of net free-vent area (NFVA) for each 300 sq ft of attic area.

2) Use as much soffit venting as possible (continuous soffit vents are best) to get maximum fresh air inflow into the attic. Place the soffit vents as far out from the walls as possible.

3) Most codes recommend 50/50 balance of lower fresh air intake vent area and upper exhaust vent area, but a split that has more lower intake venting is actually more advantageous to keep the attic space pressurized a bit, even up to a 75/25 split (60/40 is a sweet spot).

4) Use baffle vents in each truss bay to keep the insulation from blocking the inflow from the soffits and allow fresh air to wash the entire underside of the roof.

5) Provide for insulation above the top plate of the walls that has at least the same R-value (or more) than the R-value of the insulation that is in the walls.

6) Make the attic floor as airtight as posssible to reduce moisture infusion into the insulation and prevent the loss of conditioned air into the attic.

Paul

 

[Highbeam]

Good info. Pretty amazing that the code only requires 1" per 300 SF. Notice that the pitch of the roof is not part of the equation?

 

[fergus]

I've noticed about a five degree reduction in interior temps now that my attic fan is installed properly. I did it wrong the first time - the shroud wasn't tight against the gable frame allowing some air to just recirc inside the attic - DOH.


On a side note, should the gable vent not that the fan is on not have any screen? Mine does to keep the critters out. It was clogged with dirt when I re-hung the fan. I scrubbed it clean.