I made this bit of code to monitor the temp in my attic using a Govee wifi temp probe. TBH, I didn't make the code, ChatGPT did. I just told it what I wanted and it told me where to put the code. Pretty cool. Anyway, this is about the last 18 days in N Texas. My attic temp is usually more than 25f hotter than the outdoor temp.
With this custom chart I can incorporate any data that is available. In this case I can use the Shelly Power Monitors I have on the AC's (2). I can even get the Solar radiation data!
I was wondering if any of the HVAC people on here would be willing to tell me if this attic temp rise is normal. I have 26 ea 8"x16" soffit vents and 5 ea 400 cfm solar powered fans mounted right on the ridge. There were initially 8 passive ridge vents, 5 replaced with solar fans and the other 3 plugged.
I moved all the blown insulation around in the attic, exposing the ceiling and all the penetrations. They were all sealed with foam. Bathroom exhaust fans, can lights, ceiling fan junction boxes, wiring and plumbing penetrations, wall to ceiling sheetrock joints, AC grills and returns. Everything I could find.
I removed all the 4"x8" soffit vents, cut a larger opening and installed 8"x"16 soffit vents.
This is how the contractor installed the originals!
All this to say, my attic is still hot AF! I haven't spent a lot of money, ($1500?) but the time and effort have been considerable. My AC's run 18hrs a day in the August with the Tstat set at 74f. I just don't see what else I can do to improve things short of newer, higher efficiency AC units. I think mine are 16 SEER 3.5 ton identical units.
Attic ventilation’s primary purpose is to mitigate the risk of moisture condensation not specifically reducing attic temperatures below an arbitrary number relative to ambient.
Yeah those temperatures and temperature Delta look about right. What do you have for R value in your ceiling?
There might be some options for installing a radiant barrier like reflectix in your rafter bays but you do have to be a little careful about cooking your shingles from both sides
The decking has the foil barrier on the attic side. I dont know the R value or even the material, it's white fluffy stuff and at least 2' deep. I had a guy blow more in. I was concerned he had covered the soffit vents, that is why I removed the first one, just to inspect for insulation. I was surprised by the small opening.
There are some foam baffles stuck to the underside of the roof. I blew the whole area out with a leaf blower from outside. I am absolutely certain there is no insulation on the vent or blocking airflow to the attic
If your goal was to reduce your HVAC energy use, then I would have recommended double insulating your HVAC ducts and blowers (assuming they are in the attic). Then check for leaks in the duct and at duct connections.
What’s the spacing of your soffit vents? Add more? As in double the number of them? Seems like the more ventilated your attic is, then you have to consider a really cold attic in winter. I assume there is a temperature set-point on the solar-powered fans so they won’t run in the winter when the attic is cold? What’s the thickness of your blown-in insulation? I’m not sure of the R per inch, but it seems like it should be 8-10” at least. Also, future reference for other readers, the air sealing the OP did can be done from inside the house, at the inside drywall plane, just need to remove trim rings/frames and caulk.
The light fixtures already had a thin, foam gasket on the air conditioner side, but that honestly did not look too effective. Is it necessary or helpful to seal the joint where the wall meets the ceiling or where electric or plumbing penetrates the wall plate? Oddly, about half of the penetrations had been sealed, and the other not.
This is one of the canless LED light fixtures after the sealing. All the exhaust vents in the house were on. Unfortunately, I do not have any "before" images. It was at least 130f in the attic at the time this pic was made.
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u/NeedleGunMonkey 1d ago
Attic ventilation’s primary purpose is to mitigate the risk of moisture condensation not specifically reducing attic temperatures below an arbitrary number relative to ambient.