New Roofs - Power Vent vs. Hip Roof Side Ridge Vents
 

Yes, I am getting a new roof. It's original from 2004.

My insurance company has suggested that I replace my large power vent with two hip roof side ridge vents. He said it would be more aesthetic, lower my electric bill and actually function better. I have found articles on the web that seem to support this. Has anyone done this?

Any thing you can do to remove any rotating powered equipment the better, less fire hazard, lower electric bills

Have you considered solar-powered fans? They are more effective than vents and, being low powered (not mains), are not a significant fire risk.

I have the vents and no fan. I have check the tempeture between outside, garage and attic. The differences ranges up to about 10 degrees. Now the garage is cooler than outdoors in the morning and the attic is a lot hotter in the evening so a fan running in the evening might be of some help but overall I don't think a fan is needed, epically during the afternoons. Turn off you fan and measure the temps and see what happens with your house.

Facts
 

Let's discuss facts rather than make generalized statements. My facts are based upon a electricity monitor which checks power consumption 10,000 a second. I know how much a fan costs to operate, time of day, hours and minutes a day, month and year

Powered fans come in three flavors, solar, big box store power fans and efficient fans, usually found on line.

I can state unequivocally that solar fans do not operate well into the evening that a thermostat controlled fans do. In other words it quits before the job is done. Readers may love, love their solar fans but that is the cold hard truth. Not enough? Our home inspection guru who posts here is in hundreds of attics here has posted that they make no difference in perceived temp.

That leaves powered fans. But wait exactly how long do fans run in a year? 213 hours.

A big how store fan uses 380 watts or 80.94 kwh a year. At SECO rates that is 9.46 a year.

An energy efficient fan consumes 22 to 120 watts (multiple speeds) or up to 2.99 a year. Quiet cool fans on amazon.

So, cost of operation is simply NOT a factor. You have been given bad advice based upon folklore. I would retain the power vent.

Thanks for that info but how do you figure only 213 hours a year?

The energy monitor tells me what is running for how long for which days and how much it costs.

You may think the fan comes on and stays on for hours, it isn't always so. It can come on, cool the attic shut off only to come on again . A rain storm almost immediately shuts off the fan as the roof cools.

Now certainly we can debate run time for a fan set to 130 degrees vice 125. But that is not the point.

If you like discover what is on in your home, what is driving the bill. Sense energy monitor, Sense: Track energy use in real time to make your home more energy efficient., Amazon $299.

Neighbour had them put in, waste of money.

If you are referring to powered attic ventilators (mounted in your roof), don't bother. This has been researched by the energy labs. Heat is primarily transferred from the hot underside of your roof sheathing to everything in your attic through radiative transfer. An attic ventilator will not address the radiative transfer issue. Powered ventilators may also suck conditioned air from your home if the ceiling penetrations are not sealed well. Save your money.

It has been researched for identical homes built in (wait for it)


1979

Air ducts and homes in general are much more airtight then they were 41 years ago. It is a rumor that refuses to die.

Homes may be better sealed than previously but the physics of radiative transfer hasn't changed since 1979. There is a reason why radiant barriers, if properly installed, work. Power ventilators are not worthwhile because they don't address the primary mechanism of heat transfer. Reread my post as I used the words "may also suck conditioned air if the ceiling penetrations aren't sealed well ".

Ah, the difference between us is I know exactly how much radiant barriers save and you do not. Bottom line is radiant barriers will not save enough in your grandchildrens lives to pay for themselves.

I also have toured under construction homes here and have seen the sealing of the ceiling penitrations. Now if I were doing the ceiling it would be better but they certainly are sealed 'well' also the duct connections are sealed.

I am more confused than ever researching this online. Georgia has apparently even banned them!

Georgia Pulls the Attic-Ventilator Plug

Attic ventilator fans have taken a whupping in the court of building science, played starring roles on useless-products lists, and gotten roughed up in the comments sections of blogs. Now they’re gadget non grata in Georgia’s supplement to the 2009 International Energy Conservation Code.

Georgia allows solar-powered attic ventilators, but attic ventilators designed to use grid power “shall not be connected to the electric grid.” In other words, you can have one, as long as it’s not plugged in.

Dealing with the heat. Despite the compromise, the rap on attic ventilators is now anchored in code. Promoters of these machines say the devices help cool attics by exhausting hot air to the outside. However, attic-fan critics say the fans often draw makeup air from a home’s interior. During the summer, there’s obviously a major energy penalty if your attic fan is pulling air-conditioned indoor air from the living space into the attic through leaks in the ceiling.

Frequently cited research results from a study conducted in 1993 and one conducted by the Florida Solar Energy Center show that attic exhaust fans also can depressurize the living area to the extent they create potentially hazardous backdrafting conditions, particularly in homes with atmospherically vented gas appliances.

You have no idea what I know or don't know. Once again, the physics of heat transfer in the attic is dominated by radiative transfer. Attic ventilators will not address that issue. Continued rambling about ceiling penetration sealing doesn't change the physics. Got it?

Yes, that is part of it. However, people have assumed that you can save energy by trying to reduce attic air temperature with a powered ventilator. In reality, conduction of heat is less important that radiative transfer from the underside of the roof sheathing so they aren't effective.

The most effective technique is spray foam insulation on the underside of the roof sheathing with the attic sealed from the outside air. This insulates the roof sheathing so that you don't have a large hot radiator. This technique will keep your attic at about 10 degrees warmer than the air conditioned part of your house and really makes sense if your HVAC ductwork is in the attic. I speced this in my previous custom home (outside The Villages) and it is very effective. Unfortunately, it is an expensive retrofit - best done during the construction of the house.