Thread: Ridge vent AND powered attic fan?

What is the suggested wording for reporting on an attic that has both a ridge/soffit vent system AND a powered attic fan? It was my understanding that a house should have a ridge vent OR a fan, but having both interrupts the proper air flow. I generally see this setup in newer houses with gable roofs.

Dependent on age and condition, the set up may not hinder proper ventilation. However I would base my opinion on what the roof decking looked like as viewed in the attic, vapour barrier, et cetera.

Manufacturer recommendations blah, blah...
The last CE I went to had a vent manufacturer and they specifically recommended to not mix different vent type on the same roof.

Welmoed,

I can't imagine it doing a lot of harm, but it is probably a waste of money.

What is the suggested wording?

You can/will get a variety of arguments on the combination of venting. Those that will argue the fan will disturb the design efficiency of the ridge/soffit system. Those that will argue belt and suspenders. You should develop your rational for the opinion that you will offer to the client. Your wording will reflect your understanding of the various systems and how they interact in different applications. There is not a stock statement to just paste in to a report that will be a definitive statement and at the same time do justice to the client and the report itself.

There are questions that you will have to ask your self to develop your opinion.
Is the ridge/soffit system is correct for the house?
Is the insulation R30 or better?
Vapor barriers present?
Type of heating systems present?
Power vent operated by manual, thermostat, humidistat or thermostat/humidistat?
Design location of the power vent?
Is the power vent operate year round or seasonal?
Is the power vent correcting an existing problem?
Plus a few other factors not coming to mind right now.

Like Gunnar, on average it will do little harm in a practical service applicaton. Yes there is a conflict with the physics of the air movement and yes there is conflicts from manufactures positions. You will find those entrenched in one opinion or another with strong arguments to support their opinion.

Can it be bad?... Yes
Is it always bad?...No
Waste of money for installation or cost of operation, possibly.

What does your husband use in his reports?

It will be a moot point in a few years when the fan burns out!

If you think about it in a logical manner the fan is going to be expelling air from the attic. The replacement air will come in from the point of least resistance and that will be that large opening that runs the length of the roof, aka. The ridge vent! This circumvents the purpose of the soffit vents and the full stack or chimney effect that provides good attic ventilation.

Is the exhaust on a humidstat or thermostat?

Originally Posted by Scott Patterson

It will be a moot point in a few years when the fan burns out!

If you think about it in a logical manner the fan is going to be expelling air from the attic. The replacement air will come in from the point of least resistance and that will be that large opening that runs the length of the roof, aka. The ridge vent! This circumvents the purpose of the soffit vents and the full stack or chimney effect that provides good attic ventilation.

You got it Scott !
There are several primary types of attic ventilation systems available and none of them are designed to be mixed with another type system. Each type of mix will diminish the effectiveness of the designed system in one way or another.

I don’t know, I have both and it seems to work fine. The fan has both humidistat and thermostat and runs once in awhile. I do have it set on the high side and seems to only run when temps get in the 90's and the sun is beating down, or gets real humid. I think it acts more like a booster when the temps or humidity get real high to help cool the attic.

To me, it seems like it helps more in the winter when the ridge vent has 2 feet of snow on it. There is always a clear area around the power vent in the winter.

I never really noticed the air pulling down in the attic when the fan ran, always felt like an updraft. But, each roof is different.

Originally Posted by Gunnar Alquist

Welmoed,

I can't imagine it doing a lot of harm, but it is probably a waste of money.

Originally Posted by Mike Kleisch

I never really noticed the air pulling down in the attic when the fan ran, always felt like an updraft. .

Power Vents can depressurize a dwelling and pull the conditioned air up and out of the attic.
* unconditioned air is pulled into the dwelling to be cooled / heated and restart the cycle over.
$$ Dollars Out The Roof.$$

Originally Posted by Billy Stephens

Power Vents can depressurize a dwelling and pull the conditioned air up and out of the attic.
* unconditioned air is pulled into the dwelling to be cooled / heated and restart the cycle over.
$$ Dollars Out The Roof.$$

I should have been more clear. I was saying I didn't notice the air being pulled in from the ridge vent as it felt it was from the soffit vents. You can feel plenty of air movement through the attic when the fan is off. Like I said it has to get real hot or humid, you know, a classic stale day, for the fan to kick on.

My own feeling is that the ridge vent would become an input rather than an out of air flow. It maybe that the the bulk of the air entering the attic would come from the ridge vent rather than the soffit, given it is much closer (I think) to the attic fan. Should this be the case, then it is fair to say air circulation would be in the the upper 1/3 of the attic only or mostly, but not the lower 2/3.

Originally Posted by michael Rodney

My own feeling is that the ridge vent would become an input rather than an out of air flow. It maybe that the the bulk of the air entering the attic would come from the ridge vent rather than the soffit, given it is much closer (I think) to the attic fan. Should this be the case, then it is fair to say air circulation would be in the the upper 1/3 of the attic only or mostly, but not the lower 2/3.

I find it hard to envision, hot air moving up the slope of the roof sheathing, stopping its movement in that direction, just because a fan is in the path of its travel pushing air out of the attic. I find it more likely that the air moving from the soffit vent toward the ridge will supply more of the total cfm of the fan than any other source of air in the attic due to it already moving in the right direction. If the soffit or any other installed venting has sufficient opening, there is little chance of depressurizing the attic enough to draw air from the home. If any air is drawn in through the ridge vent near the fan, so what? It is outside air being drawn through the attic, which is just what you are trying to accomplish with ventilation.

It has been my observation (while not totally scientific) that when there are more or bigger holes, things leak faster! When this is related to heat out of an attic, leaking faster is a good thing.

Originally Posted by Vern Heiler

If the soffit or any other installed venting has sufficient opening, there is little chance of depressurizing the attic enough to draw air from the home. .

Guess they build em a lot better in NC.
*I see whole subdivisions if there ever were soffit vents The Siding Crew covered them over.

I probably would make an issue of it. I see more fans not connected or burned out, or blocked soffit vents that I do spend time reporting.

Originally Posted by Vern Heiler

I find it hard to envision, hot air moving up the slope of the roof sheathing, stopping its movement in that direction, just because a fan is in the path of its travel pushing air out of the attic. I find it more likely that the air moving from the soffit vent toward the ridge will supply more of the total cfm of the fan than any other source of air in the attic due to it already moving in the right direction. If the soffit or any other installed venting has sufficient opening, there is little chance of depressurizing the attic enough to draw air from the home. If any air is drawn in through the ridge vent near the fan, so what? It is outside air being drawn through the attic, which is just what you are trying to accomplish with ventilation.

It has been my observation (while not totally scientific) that when there are more or bigger holes, things leak faster! When this is related to heat out of an attic, leaking faster is a good thing.

Those fans are moving about 1200 cfm. That's a lot of air! Yes, it is pulling air from the ridge vent and the soffit vents, but in most cases it is also pulling air from the building enclosure through any little hole in the ceiling it can find. I've tested a number of these attics with the thermo controlled attic fan with a manometer and there is always a negative pressure in the attic when the fan is on no matter how many soffit vents there are.
In my opinion, there should never be a powered fan installed in any attic.
By the way, how many older houses have you seen with one of these fans and no soffit vents or maybe just a couple of well baffled gable end vents? Talk about sucking money out of the house!

Originally Posted by John Ring

Those fans are moving about 1200 cfm. That's a lot of air! Yes, it is pulling air from the ridge vent and the soffit vents, but in most cases it is also pulling air from the building enclosure through any little hole in the ceiling it can find. I've tested a number of these attics with the thermo controlled attic fan with a manometer and there is always a negative pressure in the attic when the fan is on no matter how many soffit vents there are.
In my opinion, there should never be a powered fan installed in any attic.
By the way, how many older houses have you seen with one of these fans and no soffit vents or maybe just a couple of well baffled gable end vents? Talk about sucking money out of the house!

Some of the questions I would have:

1) Was the manometer reading a differential reading or a noted drop in pressure in the attic only?

2) Where is the break even point relative to negative pressure sucking air out as opposed to positive pressure pushing hot air in? The ying and yang of it.

These are real questions, not busting on you and appreciate your joining the board.

As far as no or blocked venting in an attic, I am sure every HI on the forum jumps on this with both feet. And as Scott said, the power vent will be just another roof vent with an obstruction in three to four years anyway!

The OP, I see, has not weighed back in.

Attic ventilation is never a simple formulaic blue print. Sometimes what I see in attics defies my conventional understanding of roof/attic ventilation and insulation. I don't mess with dry attics in my reports. If I thought the fan had been there for a few years or more and I saw no moisture issues under the sheathing I'm all good.

Yes and we weren't given any info as to age of the structure or anything else relevant to whether or not its a problem. Just the facts Mam!

This is how I worded this recently:

The home has a combination of soffit vents and ridge vents installed that should theoretically support effective convection attic ventilation, but the temperature in the attic was significantly elevated at the time of the home inspection. Ideally a home's attic should be within 15-20 degrees fahrenheit of the the exterior temperature year round. The exterior temperature was around 75 degrees fahrenheit at the time of the inspection, and the attic temperature was approximately 110 degrees fahrenheit. Attic temperatures of 110 degree fahrenheit won't have a considerable negative impact on the home and its components, but when the exterior temperature is 85+ degrees fahrenheit and it is sunny, temperatures in this attic will be elevated to the point that the these high temperatures will affect the comfort and the energy efficiency of the home and shorten the life expectancy of the home's asphalt/composition shingles.

Ventilation modifications aimed at maintaining cooler temperatures in the attic would be beneficial and are recommended.

The fact that the home has black shingles and a considerable amount of west facing roof exposure is likely contributing to elevated attic temperatures.

Normally, the last thing I would recommend would be the installation of a power exhaust fan, but in this case, the installation of a thermostatically controlled power exhaust fan near the central peak area of the roof is recommended.

The best and recommended practice would be to set the thermostat to activate the fan at approximately 115-120 degrees fahrenheit. (this may seem high, but the purpose of this fan is to limit excessively high temperatures in your attic - if the thermostat was set lower, you will waste a considerable amount of energy and also interfere with the home's passive convection ventilation components)

NOTE: If a power exhaust fan is installed, it is imperative that you have good air, vapor, and thermal barriers between the home and the attic. Otherwise, moist air will be pulled into the attic from the home, and condensation issues within the attic will likely result.

NOTE: We are continually learning more about building science, sound building practices, and how to build more energy efficient and comfortable homes. Any recommendations made in this report regarding updating this home's ventilation and insulation, are made to make you aware of how this home could be made more comfortable and energy efficient - any recommendations are not suggested, or required current homeowner repairs. You are not buying a new home, don't expect it to be perfect, and don't expect a seller being willing to make comfort, energy efficiency and sustainability improvements to this home at your request as a contingency of the sale. Recommended comfort and energy efficiency related updates are updates that I recommend new homeowners make when they move in.

This is a classic example of what's wrong with the profession today.
Hunting for nonsense things to write up.
Come on people. Just tell them that the fan is redundant and turn it off.

JLMathis

What does your husband use in his reports?[/QUOTE]

Perhaps I am being overly sensitive but doesn't this seem, if not sexist, at least a little dismissive of her stature as a fellow inspector. Is it not a little like answering a question with "well what does your daddy use in his reports"?
I am pretty sure that if ANY inspector were available to her in person and she deemed that person to be a source of the answer she would already have consulted and avoided the extra step of going on-line to get help.

Originally Posted by Jeffrey L. Mathis

This is a classic example of what's wrong with the profession today.
Hunting for nonsense things to write up.
Come on people. Just tell them that the fan is redundant and turn it off.

JLMathis

Redundant? What is your suggestion for the full pitch hip roof with an attic of 1200-1500 sf. with a ridge vent that is only 6-8 ft. long?

Originally Posted by Leigh Goodman

What does your husband use in his reports?

Perhaps I am being overly sensitive but doesn't this seem, if not sexist, at least a little dismissive of her stature as a fellow inspector. Is it not a little like answering a question with "well what does your daddy use in his reports"?
I am pretty sure that if ANY inspector were available to her in person and she deemed that person to be a source of the answer she would already have consulted and avoided the extra step of going on-line to get help.[/QUOTE]
Perhaps she has enough sense to question everyone, including her husband! I would like to know his view as well, and whether her opinion has been changed or strengthened.

Vern, my pressure measurements are always made With Reference To another space. So in measuring attic pressures I'm doing them WRT the building enclosure.
The answer to your second question would depend on the tightness of the air barrier - ceiling -below and the strength of the stack effect, both in the building enclosure and the attic above.

The postings in this thread, as is true with many other, prove the point made 2000 years ago by the Roman architect Marcus Vitruvious Pollio. I quote with location changes only:

These are properly designed, when due regard is had to the country and climate in which erected. For the method of building which is suited to Canada would be very improper in Mexico, and that in use in Chicago would be absurd at Houston: so in other parts of the world a style suitable to one climate, would be very unsuitable in another: for one part of the world is under the sun's course, another is distant from it, and another, between the two is temperate."

We should all remember this quote when we write our comments.

We also might consider why we pay so much attention to ventilating attics. After all,the primary heat source in the attic is Radiant Heat. You can't exhaust Radiant Heat with air movement.

Originally Posted by Welmoed Sisson

What is the suggested wording for reporting on an attic that has both a ridge/soffit vent system AND a powered attic fan?

For me it'd be "Satisfactory".

Originally Posted by Leigh Goodman

What does your husband use in his reports?

Perhaps I am being overly sensitive but doesn't this seem, if not sexist, at least a little dismissive of her stature as a fellow inspector. Is it not a little like answering a question with "well what does your daddy use in his reports"?
I am pretty sure that if ANY inspector were available to her in person and she deemed that person to be a source of the answer she would already have consulted and avoided the extra step of going on-line to get help.[/QUOTE]




Leigh,
Since I posed the question in posting #5, I felt I should respond.

Yes you are being over sensitive. If the OP was male and had a wife (female). I would have asked the same question if I knew the partner was in the business. I am making an uninformed conclusion/assumption as to marital status. Maybe I should have made reference to "partner" instead of husband (((( Its a brave new world for associations and titles))) and thus removing gender identification, or maybe not.

As far as sexist or dismissive, you may need to be a little introspective as to why you would jump to that conclusion.

The OP is one of the very few women that post in the forum. Granted there are a few members that will make snarky comments to female posters, but then they will also be snarky and condescending to the male members.

The request for what the OP had access to was out of curiosity due to my personal opinion that there is not a good stock (copy and paste) statement due to the many variables involved. As has been demonstrated there are quite a few opinions about the physics and function of combining venting methods. The exception being that after determining if the ventilation systems being used are effective or not and not wanting to offer a narrative, then offering the following may be sufficient. But it does depend on understanding what is right and what is wrong.

"The roof/attic ventilation methods consists of both active and passive systems. The attic/roof ventilation systems is appropriate/not-appropriate for the structure." In other words it works (satisfactory) or it doesn't (unsatisfactory). Then let the client ask for an explanation of the statement.

Originally Posted by John Ring

We also might consider why we pay so much attention to ventilating attics. After all,the primary heat source in the attic is Radiant Heat. You can't exhaust Radiant Heat with air movement.

You hit it right with the radiant heat. Keeping the air temp close to outside will take lots of air flow and does nothing to combat radiant heat flow. Air sealing the attic floor and using an insulation that blocks radiant heat transfer will do more for comfort, energy savings and durability than using a fan. Cellulose will block radiant heat better and is also better suited to attic conditions than is fiberglass.

Originally Posted by Robert Hronek

You hit it right with the radiant heat. Keeping the air temp close to outside will take lots of air flow and does nothing to combat radiant heat flow. Air sealing the attic floor and using an insulation that blocks radiant heat transfer will do more for comfort, energy savings and durability than using a fan. Cellulose will block radiant heat better and is also better suited to attic conditions than is fiberglass.

The problem is that the home inspection is to identify components or systems that are not functioning as intended. Radiant barrier is not required even though it is probably better at reducing heat load than insulation and venting. Installing radiant barrier in an older attic can be very difficult and expensive to do correctly so we are left with what is required; insulation and ventilation.

Originally Posted by Russell Nicholson

You got it Scott !
There are several primary types of attic ventilation systems available and none of them are designed to be mixed with another type system. Each type of mix will diminish the effectiveness of the designed system in one way or another.

But what about reversing the gable fan? Have it suck cooler air into the attic forcing the heat out at a faster rate. If not at a terribly high rpm (CFM) then it will not pressurize the attic much to cause an improper air flow/ out of balance condition. What are your thoughts...

Older homes typically have gable vents. A thermostatically controlled fan on one end was popular for a while and still seen with some regularity.

Many of the above homes will have enclosed soffits (mineral/cement shingle). Now a roofer comes along and adds a ready made ridge vent to terminate his roofing job. He may or may not cut the roof decking to accommodate the ridge vent. Soffits still don't vent but may have been covered with vinyl vented soffit by the vinyl siding guy who visited a few years earlier.

As posted previously the fan is probably just a waste of electricity but not doing any damage. Seems to me you would want the attic space at the same temperature as the out of doors but hot enough to prevent condensation. There is no 'ideal' design so the visible results will dictate whether or not it works.

my 2 cents