Question on attic ventilation

[Doug Steckel]

Hi All,

I have a question on attic ventilation. We just fired up the air conditioner in the new home and nothing. I'll cut to the chase and say that I think much of the problem if not all is inadequate attic ventilation. I think the attic unit and flexible, insulated tubing are just a giant heat exchanger taking pretty cool air at the unit and warming it by the time it gets to the vent. I felt the air at the vent this morning before the attic heated up and it was noticeably cooler. I'm sure that the attic had cooled down a bit over night.

Today when I got home. Outside temp - 91 Temp at vent - 81 Temp in attic - 119

We have a hip roof type, I guess that's what it's called, w/ about 20' of ridge vent. (The 1" thick floor buffer material like stuff in the ridge vent) There are soffit vents most of the way around but most were also blocked with insulation. Tonight I cleared most of it. I'm sure that will make some difference but I'm still unsure if we have enough ridge venting to cut it. I've heard you need about 1 sq. ft of venting (both for soffit and ridge, not combined) for ever 300 sq ft of attic. Is that attic floor space or attic roof? They aren't always the same because of cathedral ceilings cutting into some of that.

Anyway, besides that question any other ideas, insights, should we have to add additional venting, would be appreciated.

Thanks to the group in advance!

Doug

[Glenn]

The attic may be hot but 119 don't sound too unreasonable on a hot day. I've certainly been a bunch of them a darned sight hotter. The first thing I would do is get some good blanket insulation, wrap one run from the air exchanger and see if that makes a difference on that run. I'm betting it will. Then raise hell with the builder for a poor insulation job.

[Joseph Meehan]

119 is not at all bad.

What is "Temp at vent" and how did you measure it?

[Doug Steckel]

Temp at vent = Temperature at output at ceiling vent by taping thermometer to vent for 10 minutes. Temp in house by the way was ~ 86.

[Al Bundy]

"Doug Steckel" wrote in news: [e-mail]:

You should see an average minimum of 16 degrees between the air intake and the vent outputs is the feeling I get from HVAC people.

As mentioned, 120 in an attic on a sunny hot day is not high.I've heard it can get to 140. I've been up in an attic on a sunny 95 deg day with the HVAC guy in the afternoon. Sweat was literally pouring off me. Then he fired up the mapp gas torch. You never complain about the service fee after that experience.

Anyway, assuming you have good airflow from the vents, if flexible duct is in the attic I would guess it has to be r6 or better. If the hard plastic duct it should be wrapped with insullation.

If the attic unit has a seam gap or something similar, it's possible is's sucking hot air and mixing it with cool.

Has anyone looked at the compressor and put gauges on it? It may be low on freon (or whatever they use now). If it is as little as 1 lb low, the freon may not hit it's "flash point". AC guy showed me that one since he saw I was interested. I had a unit that was putting out cooler air but only a few degrees (not the 16 deg differential). He put the gauges on it and said it was down a pound. Told me to put my hand on the freon line coming from the compressor and it felt cool to me. Says keep my hand on it while he pumps in another pound. Boy did that go from cool to cold.

Just some thoughts and experiences...

[Craig K.]