Increasing Soffit Ventilation for Attic Furnace without increasing ridge vent

Old 09-25-12, 01:30 PM
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Increasing Soffit Ventilation for Attic Furnace without increasing ridge vent

We have an attic furnace with a ridge vent at the top of our roof. Our soffit ventilation has one vent for every 5 non-vented pieces. House has the issue with the further the room is from the furnace the colder the room is and so we have uneven heating. One room is really warm, another just ok. We have been told it isn't an insulation problem but a ventilation problem.

We live in Pennsylvania so we get some cold days and snow. We haven't had many issues with ice but there are a few places that ice does develop in the winter (the ice is minimal but I know it is there)

Here is our question - we need to replace siding on the rear of our house due to hail damage. Our contractor has recommended that we vent the entire soffit on the back of the house to help with the ventilation as long as we are doing the siding. Will this help or cause additional issues as the front and side soffit will not be vented? Should we wait and vent the entire soffit? In addition, we only have the 1 ridge vent and another contractor recommended we ridge vent the top and 4 corners which we would not be doing at this time. Again, should we wait and do this all? Will venting just the rear of the house soffit be ok without causing any issues.

Thanks for your help.
Old 09-25-12, 02:26 PM
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Your attic ventilation has absolutely NOTHING to do with the conditioned air inside the house. Uneven heating is due to your HVAC... either the system itself, or the ductwork, -the supplies or the cold air returns. Just based on what little you have said, I would imagine that the rooms closest to the unit need dampers to reduce the amount of airflow, which would increase the amount of heat getting to the end of the line.

The recommended ratios for attic ventilation (soffit and ridge venting) vary depending on who you ask, but generally, the FHA rule for attic ventilation is based on a formula of 1 sq ft of ventilation for every 300 sq ft of attic space. Half of that area should be intake and half should be exhaust. So for a 1500 sq ft attic, you would need 5 sq ft of ventilation. have 2.5 sq ft of intake and 2.5 sq ft of exhaust.

Some local codes may recommend more ventilation 1 to 150, so follow your local code.

In general, many people think more ventilation is good, but in reality, too much ventilation can also cause problems. Attic ventilation can increase heat loss from the home, it can blow your insulation from one side of the attic out the other. Having adequate insulation installed and having baffles installed is the key, for starters.

Rather than making a blanket recommendation, I would calculate your needs and proceed based on the formulas above.
Old 09-25-12, 02:31 PM
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Hi cb and welcome to the forum,
I'm a bit confused so will ask some questions.

More venting would make the attic colder, so how is that supposed to increase the heat delivered?

Placing a forced hot air heating system in a cold attic requires some special attention. Essentially it is sitting out in the cold. Ducts, even when wrapped in some insulation are almost always not air sealed and have far too little insulation. This all sounds bad, but actually it is good, because you have some areas that can be improved to make a difference.

How old is the house? That will help us with the construction details. And what style is the roof?
I assume there are a lot of ducts up there, give us the layout.
What do you have for insulation, both the house and the furnace and ducts?

Ventilation is necessary, but may not be the solution to this particular problem. With all of that heat up there you may be avoiding the ice dams by melting off all of the snow.

Air sealing the house to attic. Adding more insulation to the attic if necessary. Air sealing those supply and return ducts and then insulating them as much as possible. Not sure what can be done to improve the furnace itself, perhaps some pictures.

From your description, your current ventilation is minimal, especially since the furnace has to draw from it for combustion. Adding more as described might change the path the incoming air is following, thus less venting on some areas of the roof and more venting on others.

You should have 1 sq ft of net free vent area for every 150 sq ft of attic floor. Evenly distributed with half high and half down low.

Old 09-30-12, 01:43 PM
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While heat loss from the attic space is a definite concern, it sounds like the root of your issue may be a poorly designed (or poorly insulated) duct system. Posting pictures of your attic would be helpful.

The insulation depth for the ceiling, insulation for the ductwork (if the ductwork is sealed properly), duct design and even thermostat placement are significant issues.

I would suggest contacting an HVAC contractor or "Energy Specialist" (contractors that specialize in these specific issues) to inspect. You'll likely find that you have several factors contributing to the heat loss.
Old 09-30-12, 03:31 PM
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Yeah, I think the word 'ventilation' was mis-used or mis-understood, as it is the HVAC system which needs the work here, not your attic.

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