
Attic Venting In Your Home
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Powered attic fan click here
The importance of
venting
your attic cannot be overlooked. In cold climates, improper
venting can lead to moisture build-up which causes mold to grow, wood
rot in extreme cases or even ice in the attic insulation.
In hot dry
climates, stagnant air
can dry out your trusses, increase your energy costs for air
conditioning
and make your house uncomfortable.
Let's start with an
understanding of basic physics: Hot air rises. But why? Heated
air rises due to a differential in density (mass), which causes an
upward movement of the fluid (air is a fluid). Like a lava lamp,
the colored liquid is heated, rises to the top, cools off (density is
increased), then falls back to the bottom.
Think of the force required to raise a hot air balloon off the ground
with 10 passengers, the tanks of propane, the weight of the basket and
the balloon. Pretty impressive force if you think about
it. Should be easy for hot air to rise out of your attic
right? Driven by the density differential, the exhausting of the
hot air should bring in fresh air where vents are located around the
base of the roof (soffit).
There is no
"pressure" that drives hot air out of an attic. The pressure
(atmospheric),
inside your attic is the same as it is outside (based on a
no wind condition. Wind blown across a roof can create a positive
pressure on the windward side and a lower pressure on the lee
side). Only the differential bouyancy of heated air over the temperature of ambient
air is different.
Using a tracer gas and smoke generators, we
have documented all types of attic venting, the appropriate sizes that
work in hot climates and have posted our findings below.
This is not a scientific study but observations made over the study of
hundreds of homes in all types of climates.
Click here to study the
UBC code
on attic venting.
Our Field Proven Results and Recommendations: (if using a radiant barrier)
w for
how many to add per square
foot of attic area.
Despite the small area of these vents, the vertical stack of this vent allows for the fastest flow of air from a hot attic. For best performance, these vents should be placed as close to the peak of the roof as possible.
RIDGE VENTING
This popular method of attic venting is catching on all over the
country. Easy to install, looks good, inexpensive, doesn't
leak...only one problem: They don't work. Ridge vents
defy gravity, physics and basic thermodynamic principles as outlined
below:
Since our reflective attic
insulation products increase attic
temperature by the rejection of infrared heat, attic venting has played
an important aspect of looking at the big picture. Getting rid of
this heat is very important to reduce energy consumption and increase
interior comfort. We have found through experience that
homes with ridge venting are historically the hottest and emails from
our customers who have read this site reinforce this over and over.
Puffing tracer gas inside the attic at 2pm just under
the opening shows the air in the attic to be stagnant. Stay
away from ridge venting unless your home is built where there is a
constant breeze as the air moving over the roof will tend to create a
vacuum on the lee side of the roof which will draw the hot air out.

Ridge Venting vs. Dormer
Vents
Ridge
vents are very attractive, easy to install and makes all the
sense in the world...they just don't work. Everyone will agree
hot air rises. Where best to put an attic exhaust vent? At
the peak where the attic air is the hottest?
Sounds logical except for one basic fact: Hot air rises, it
doesn't go down. A
ridge vent design dictates hot air must fight gravity, travel down from the peak of the roof in
order to
escape. This of course is unrealistic and so is expecting this
type of vent to be effective. The only "driving force" that makes
hot air leave an attic is the differential density of the 140F attic
compared to the more dense ambient outside air. If you have
any doubts (as we did), as to the function of this type of vent, do
what we did: Buy a 2000 CF smoke canister, place it in a coffee
can in the center of the attic and light it. Then go outside and
wait for the smoke to come out of the ridge vent. Better
bring a lunch, plenty of water and a good book....you will be there
awhile.
The roof you see above was built using a continuous ridge
vent. When the hot weather came in April to this Phoenix home,
the attic was like an
oven despite the fact the intake venting (soffits), were doubled to
insure good flow.
We cut the first hole in this roof about noon to install the dormer
vents you see above and the air came out so fast if you kicked the
sawdust into the hole it would hit you in the face! Proof
that the hot, stagnant attic air is not being vented properly and being
trapped by the ridge vent design. Further, the steeper the roof
pitch, (like homes in Texas or the older Cape Cod homes in the
Midwest), the less the ridge vent will work. This
observation is
based on fact, physics and common sense. Hot air does not fight
gravity. Further, in cold climates, it only takes a few inches
of snow to
render ridge
vents completely useless....when you need them the most to keep the
roof from getting warm, melting the snow and creating ice dams.
Inadequate venting is a major contributor to costly ice dams.

Dormer vents installed on a home in
Dallas where the hottest attic air temperature was ever recorded by our
NRG Auditor. Two reasons:
1) The underside of the roof decking was sprayed with silver radiant
barrier paint thus lowering the emissivity and increasing the convective
currents (and energy use), in the attic space.
2) Ridge vents trapped the hot air. Ridge vents rely on some
unknown
source of the universe to
drive hot air down then out.
The dormers shown here dropped the attic temp by 42 degrees.
Solution: TCM6 over the
insulation
and Dormers.
SOFFIT VENTING
Many homes do have
soffit vents but are blocked by improperly installed insulation.
Proper
attic ventilation is
necessary and the products listed below will help.
This procedure gives your
attic the air it needs to vent properly. In cold climates this
equates to adequate moisture removal and the elimination of the
associated problems like mold growth and wood rot. In hot
climates, the super heated attic air
can flow out the upper vent (if
you have them), and draw cooler air in around the house. This
what your architect and builder expected. However, in most homes
the insulation contractor may have plugged up some or all of your
soffit vents. Our home energy auditors have found most homes have
this problem. Check yours or click here to
schedule an energy audit (if you live in the Phoenix area), for
your home. If you have questions about your existing attic vents,
take a
few digital pictures and send them to us for evaluation. This
will be a
free service as we fine tune our online NRG Audit coming soon.
Take
advantage of our knowledge and free advice! Please, no more than
five
pictures. Take one of each side of the home noting to make photos
of the
soffits vents (if any), gable vents (if any), and one or two shots of
the attic.
Step by Step Soffit Venting




This vent can be applied to 3/12 and 4/12 pitch roofs. 5/12 now available. NOTE: We do not ship dormer vents, Home Depot has them.
Dormer vents installed
correctly on the back side of an apartment building. The lower
vents on the roof are intake vents, the upper vents are exhaust
vents. This type of venting, if correctly sized to the attic size
and volume, can adequately vent the hot air out during the summer and
moisture during the winter.
These are not seen from the front of the building and therefore do not
detract from the aesthetics.
POWER VENTING
This shows a typical home store attic fan installed on a gable vent
inside the attic. Although the mounting looks secure, the
application is incorrect since
the space around the fan is not blocked off. The fan will create
a
negative pressure behind the fan and will draw air from the closest
point, in this case, from
vent openings around the fan.
This means very little air will be
exhausted from the attic and
most of it will be drawn in around the fan.
The open area around the fan shroud (the round ring), needs to be
blocked off with cardboard or wood to make this type of installation
effective.
Power Fans:
Natural attic venting is best but in many homes a powered attic
ventilator is more cost effective, especially in tile roofs.
STAY AWAY FROM
UNDER POWERED SOLAR ATTIC FANS, THEY JUST DON'T MOVE ENOUGH
VOLUME. Great idea, not enough power.
We now import a
vibration free, powerful, reliable powered attic fan manufactured in
Germany. This attic fan is unlike any other available.
We include an adjustable thermostat and an optional mounting box with
this system. This fan features an external rotor to which the fan
blades are welded. This unique design reduces blade flex
and vibration and eliminates one of the shaft bearings.
The bearings are sealed and never need attention. Install it, set
the thermostat and forget about it.
Costs 2 cents per hour at .10/KWH to operate! That's less than a
quarter per day.
To place an order click here
14" 1800 CFM
fan shown here
In homes that have gas appliances such as
water heaters or furnaces in the attic, great care must be taken to
insure adequate intake venting (gables/soffits), is provided so as to
not create a
negative pressure that will draw combustion gasses down the chimney of
gas
appliances. Installing an attic fan in this application has
the potential for fire or filling your attic with carbon dioxide.
Just make certain there is sufficient intake openings to circumvent
this potential hazard.
Construction
Features
| Fan Model |
RPM | Volts | Max. Watts |
Max. Amps |
0" | .100" | .125" | .25" | .375" | .5" | Sones** |
| 8" PAV | 1550 | 115 | 45 | 0.41 | 304 | 246 | 224 | 74 | - | - | 4.1" |
| 10" PAV |
1500 | 115 | 68 | 0.62 | 624 | 558 | 533 | 377 | 132 | - | 7.9 |
| 12" PAV | 1400 | 115 | 130 | 1.19 | 1208 | 1069 | 1030 | 797 | - | - | 9.4 |
| 14" PAV | 1200 | 115 | 245 | 2.24 | 1839 | 1654 | 1599 | 1295 | - | - | 9.6 |
| 16" PAV | 1400 | 115 | 458 | 4.19 | 3054 | 2882 | 2839 | 2570 | 2198 | 1699 | 12.0 |
| 18" PAV | 1550 | 115 | 698 | 6.39 | 4115 | 3895 | 3840 | 3549 | 3239 | 2908 | 14.3 |
| 20" PAV |
1100 | 115 | 435 | 3.98 | 3693 | 3368 | 3279 | 2775 | 1429 | - | 10.7 |
| 20" PAV |
1450 | 115* | 916 | 8.39 | 4949 | 4682 | 4615 | 4274 | 3917 | 3445 | 16.4 |
| 22" PAV |
1000 | 115* | 756 | 6.92 | 5629 | 5248 | 5153 | 4432 | - | - | 12. |
| 25" PAV | 1000 | 115* | 1134 | 10.38 | 7858 | 7355 | 7230 | 6567 | - | - | 14.8 |

10" fan 624 CFM $287
(sufficient to ventilate attics up to 800 square feet) NOTE: This is close to the
measured CMF delivery of a home store fan that advertises 1200 CFM)
12" fan 1208 CFM $305 (sufficient
to ventilate attics up to 1375 square feet)
14" fan 1800 CFM $349 (sufficient
to ventilate attics up to 2800 square feet)
16" fan 3054 CFM $397 (sufficient to
ventilate
attics up to 3950 square feet)
Pricey? They sure are, you could buy several home store fans for the price of one of these....then plan on replacing it every year because that's how long they last (see testimonial below). I don't know about you but I would rather have a root canal in Mexico than spend a Saturday morning in a hot attic replacing the fan under warranty. Once this job is done, you never want to see it again. This one you won't because of the quality, the thermostat and sealed motor bearings that never need lubrication.
If you open the box
upon delivery of this item are not totally impressed with the
craftsmanship and quality, return it for a full refund. We'll
even pay for the return shipping! We are that confident of this
item. We do not offer any product on our site that have not been
field tested in all climates.
We fabricate this sheet
metal fan box for our Phoenix installations and thought we should
offer it to our online shoppers as well.
The design allows for a
smoother discharge of air as it fully takes advantage of the
aerodynamic design of the shroud and large side
flanges makes it much easier to install.
Cuts the installation time in half.
This is how the fan will look when you open the
box. The fan is mounted to the sheet metal box and there is
15' piece of 14 gauge Romex already pre-wired to the fan and
thermostat.
We even provide a 2"x4" mounting box to mount the thermostat so all you
need
to do is run a 115v power supply to the thermostat, mount the fan
shroud to the wall, set the thermostat to 105f and call it day.
To place an order
click here
This just in from a customer in the Midwest:
If you live in Phoenix, click here to find out
about our Home NRG Auditsİ. Then, after your attic is
properly vented, check out our revolutionary Radiant Barrier Chips
or our latest patented energy product, Thermal
Control Membrane to
further increase your home's comfort and efficiency.
To place an order click here
Web page
design and
maintained by B Rad Design Group
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Horizon
Energy Systems. All rights reserved.
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Information in this
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