Ask the Builder: Photo voltaic attic fan not going to be ample for the job

QQ Can you overcome the fog of confusion about solar attic fans? Do they really work or are they mostly hype? What does it take to really cool an attic? My husband really thinks buying a solar roof fan is a great idea, but I don’t want to waste the money doing little or nothing. – Bridgett W., Tampa, Florida


I remember when the madness of a solar roof fan was hotter than the surface of my roof at noon on a summer day. The manufacturers sent me fans to test it, and I tested it. The results were exactly as I expected. The solar roof fans all moved less than 1,000 cubic feet of air per minute and did nothing to lower the temperature in my own attic.

The sun’s infrared rays are strong. You can raise your roof temperature to over 160 ° F. I’m pretty sure I can get over 180 ° F with my thermal imager in certain situations.

This heat is transferred to the roof cladding and then to the roof frame elements. Essentially, your entire roof structure gives off low infrared heat, just like the embers around the campfire.

In order for the attic fans to work at maximum efficiency, they must be on a south facing roof slope if you live in the northern hemisphere. When a cloud blocks sunlight, the fans slow down or stop. When the sun goes down in the sky – when the attic temperatures are highest – the fans slow down. The fans have to run at full speed late in the day and into the evening to bring air into the attic and cool all the wood as quickly as possible.

I tested a solar roof fan that moves 800 CFM of air. I took temperature readings in my attic because the fan was running on a cloudless day and the readings never went down even though the fan was moving at top speed.

If you want to significantly lower the temperature in your attic, you have to do what chicken farmers do. They move tens of thousands of CFM through the barns where the chickens live. Some of the high speed fans have blades larger than 4 feet in diameter!

I have data and videos on solar attic fans on my website

QQ My new home is under construction and I stopped by to check the progress. The plumber had just plugged in all the drainpipes. I was surprised to see how many pipes rose through the walls and into the attic. I was upset that my money was being wasted, but the builder said the pipes were vent pipes. Little did I know there was so much plumbing behind the plaster in my current home and attic. Are the ventilation pipes necessary? What do you do? – Ted B., Tewksbury, Massachusetts


Vent pipes provide your sanitary system with air. Every time water drains through the pipes on its way to the sewer or septic tank, it pushes air in the drain pipes out of the way. This air needs to be replaced and the best way is to get it out of the atmosphere above your home.

If you didn’t have ventilation pipes in your home, the water would drain slowly and air would be drawn into the system through other fixtures in your home. The movement of water from a flushed toilet creates a significantly short-lived vacuum in the system that can effortlessly sip water out of a vanity or tub trap. You may have heard this sucking sound in the past and not realized what happened.

Vacuuming a trap dry can allow sewage gas and bugs to enter your home. This is why ventilation pipes are so important.

Installation regulations in certain locations allow mechanical vents on or under certain fittings so that installers do not need to install all of the vent pipes. I’m not a fan of these shortcut devices because they have moving parts. Anything with a moving part will fail at some point. I regularly get e-mails from people with sewer gas odor in their homes from fancy mechanical vents.

There is no substitute for a traditional vent pipe system with at least one full size vent pipe. There are no moving parts. I am only a few months away from installing this old-fashioned, tried and tested system in my daughter’s new home.

I have tips and a video of vent pipes that I took that shows you all of the vent pipes in a new home posted at

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