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Question DetailsAsked on 8/28/2013

Roof Ridge Vent vs Power fan for attic ventilation in PA

We are replacing our roof and installing a smart vent system (we do not have any soffets currently) the roofer suggested that we do not replace the ridge vent since we already have a power fan. Or we use a Ridge vent and remove the power fan. Which is the better option?

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4 Answers


AS old energy conservation freak , ridge vents trump powered fans Every time, They do not requre energy to function and pull air from the highest point of the home. Am somewhat confused in that you dont have soffit ventilation. Is you home lacking an overhang to put one? A smart system would have its own advise but wonder how it functions drawing heated air from the attic with a power vent pulling against it?

Jim Casper

ps see my blogs for some ideas


Answered 7 years ago by jccasper


The purpose of attic ventilation is to remove moisture and warm air leakage. Most important is the attic space must have at least 12" insulation and AIR SEALED to prevent air infiltration from the living space below- This means sealing plumbing/electrical penetrations, chase areas, and framing top plates. Most roofers do not understand building science and air infiltation issues.

For the ridge vent to work properly, you must have adequate soffit ventilation- usually requiring baffles placed between rafters and no insulation blocking the soffit ventilation- the natural convection from the soffit to the ridge vent will remove the moisture vapor from the living area and make sure any bath vents are vented OUTSIDE the attic. Proper soffit ventilation will also minimize ice dams as well. With a properly sealed/insulated attic with soffit/ridge vents- NO power fan is necessary and any fan will render the ridge vent useless since it will stop any convection.

Answered 7 years ago by hosey


SmartVent has several products - not clear if you are talking the ridge vent product, the roof-mounted fan system, or the "whole house" fan system.

As the other comment said, something is not clear to us here. If you have ridge vents you should not need a fan, or if you do, then it should be turned on by excessive heat or humidity sensors only if the normal attic ventilation is not working adequately. However, for a ridge vent to work you really need soffit/eave venting, preferably with as much open eave space as possible, otherwise you will only get a minor amount of flow in the end gables and out the nearest section of ridge vent, doing nothing to provide ventilation mid-attic.

If you cannot put in soffit/eave vents because of eave configuration then the ridge vent is going to do little as it has no air source, so positive ventilation with a fan system is probably needed. Unfortunately, assuming it is a gable-to-gable ventilation system, if you have a ridge vent it is going to short-circuit the fan, as instead of pulling air from one gable and venting it out the other it will suck from the nearby ridge vent and not affect the other end of the attic significantly at all. Therefore, the two (ridge vents and fan) are largely incompatible with each other.

If you can open up eave venting (with appropriate eave baffles or troughs to protect against insulation blocking the air flow), then go with the ridge vents. If your roof is built so you cannot readily put in eave vents, then you really need help from an HVAC expert.

It sounds like you are in the middle of the roofing job, so have to make a decision right now. If so I would go with the ridge vents (which can always be easily blocked fromthe inside with visqueen if needed), and then if eave vents cannot be put in I would install a pressurized (fan-driven) thermostat/humidistat and timer controlled air distribution system at the eave location. I have done this on several cold-climate low-slope or flat roof buildings with rafter spaces, It works essentially like a french drain in reverse - perforated plastic pipe is laid along the attic perimeter where the rafters meet the wall, and a thermostat and humidity controlled fan blows outside air through the pipes releasing it along the inside of the eaves, providing an air source for ridge or center-roof ventilators to release the air. The system is also co-wired with a timer so it automatically runs every 30 minutes or so for 5 minutes to move some fresh air regardless of humidity or temperature in the attic. Not the ideal, but some roofs are built really stupidly with no thought to ventilation, and indeed, prior to the 70's or so attic ventilation was avoided scrupulously in many parts of the country.

Answered 7 years ago by LCD


This seems obvious to me that if you are employing a technical solution like smart vent, THEY are the ones that should advise you how to best amplify their system and what might compromise it's effectiveness.

When reading that they are "drawing attic air" it seems they would have a LOT to say about what you do to affect that air. I see on the website they have a Contact Us tab to select.

"Drawing air from the roof cavity, outside or even from your lounge in Heat Transfer mode (if installed), SmartVent will choose the warmest air in winter and the coolest air in summer providing a complete year round ventilation solution.

Answered 5 years ago by tgivaughn

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