I have a house from the 60s. It is 30 feet deep and 60 feet long. I have
3'x3' gable vents in each end of the house. Plus there are two roof
vents about 8 to 10 inches round.
There are no soffit vents what so ever. Reading on the Internet only
talks about the benefits to roof its self. I would like to know how much
it would help with the temperature in the rooms just below the attic.
The walkout basement family room and bedroom are always a good 15
degrees below that upstairs and the A/C runs all the time.
Will the vents help?
The vents would help. Hot air rises, but if there is no way for cooler air
to enter so the hot air can exit the higher vents it gets trapped. That
said, without knowing the A/C configuration for supply and return vents what
you'll actually observe in the effect on cooling may not be that great. The
basement rooms that are at least partially surrounded by the cooling effect
of the earth will always be cooler than the upstairs rooms that are not.
Improving the air flow within the house (drawing the cool air up to the
upper levels and the warm air down to the lower levels) will probably have a
more dramatic effect on the cooling.
That said, there is also the risk of moisture build-up in the attic with
insufficient ventilation. Installing the soffit vents will help reduce
this, keeping mold, rot, and other moisture related problems to a minimum.
Depends how much insulation is in your attic. This is more important in
winter. In summer if your ceiling is warm there is no convection (warm air
rises), in winter if the ceiling is cool than cold air sinks.
The standard for venting is to have 1/2 of the
vent space near the top and 1/2 near the bottom of
the area being vented. My house had end gables
and a powered roof vent. When I reroofed the
inspector said I needed more venting, so I added
vents in the soffits. The change was remarkable
in controlling heat gain (single level ranch style).
To answer your question, you need the soffit
vents. Vents in just the upper area is like
having a car with brakes only on the rear axle.
The comparison of the walk-in basement with the
upper story is not a good one because the ground
is a heat sink and provides a lot of cooling. If
you A/C is sized for the house, you should have no
problem keeping the upper story any temperature
that you want providing you don't live in some
area where the temperature goes to 110 day after
day. And, the A/C should not run constantly. A
key component in keep the house cool is how much
and how well the attic is insulated from the
ceiling below. You should have at least 12" of
insulation and depending on the severity of your
winters and summers the insulation should be
increased 3" to 12" more.
Didn't like that comparison? I thought it was
You get good circulation only between the lower
and the higher vents. If there are no lower
vents, the circulation in the lower part will be
poor to non-existent.
The point to having soffit vents is that hot air naturally rises,
creating lots of natural convection for free. If you bring cold air in
at the top, sure it will help, but first, you're gonna need a powered
fan to do that, and it's not nearly as effective as bringing it in a
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