Was just talking to a HVAC guy and he referred to some study that said
the cost of running power ventilation exceeded the cost of just
turning down the AC. Someone shared the idea of solar powered vents
which I've looked in to but I think my first best move is to improve
the passive ventilation. I have only vents at the eaves currently so
will add soffit and maybe, in time, ridge vents.
What do you think?
my ridge vent helped a lot
I think ridge vents depend upon the part of the world in which you live. In
hurricane country I'd avoid ridge vents, which have proven to be a weak spot
in hurricanes. My contractor referred to them as "roof zippers."
The problem with a fan is that it must exhaust massive amounts of air to be
effective. Assuming an 1800 sq ft house with a 6' attic at the peak, we're
talking (roughly) 6 x 1800 x 0.5 = 5,400 cu ft. An attic exhaust fan should
change the air every 2 minutes, so you'll need a fan that moves 2,700 cu ft
of air per minute. That's a good sized fan.
"For well-insulated ceilings (i.e. insulation levels of R-19 or above) it is
doubtful that a power ventilation can be justified economically. "
Because if the area is being heated faster than you can remove the heat, you
don't accomplish anything.
I don't know that 2 minutes is the optimum value - it may be one air
exchange every half-hour or it may be twice per minute. I'm sure somebody
has figured it out. Research is called for.
Based on the comment about the power required by the power
ventilation, I'm abandoning all thoughts of that. However, the HVAC
guy also said that the standard for insulation was R19 but not it's
R38. I need more insulation!
While I was installing the soffit vents, my thermometer next to me was
reading 108! I looked online and the heat index was 119. Guess
that's why the AC is struggling. :-)
Always a good idea, BUT there's a point of diminishing returns. The R19
advocate says effectiveness drops off at about the R19 point. That is, you
get the biggest bang for your buck at the (up to) R19 level.
I wonder if this idea might provide some insight: Install a remote-sensing
thermometer beneath all the attic insulation, next to the ceiling drywall.
This might provide an indication of exactly how effective the insulation
Keep going! You can't have too much soffit venting!
Where does that come from? It sounds pretty aggressive to me. I think
an attic fan can make a big difference even if it's only capable of
changing the air a couple of times an hour.
IMHO, an attic fan isn't a panacea, but it can be useful in the mix.
I know mine has relieved some of the stress on my (much more expensive
to replace) A/C unit.
I'm also a big fan (no pun intended) of radiant barriers.
so you'll need a fan that moves 2,700 cu ft
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.