Very interesting concept, but let’s cross the street and view it from the other side.
(If you note, it says the venting “can” pull a vacuum. It doesn’t say that it will.)
Can you tell me which has the greatest energy loss, stack effect depressurization:
(26 x HDD x Fuel Price) / (N x Seasonal Efficiency) x .06
Or thermal bridging (conduction):
(AREA (sqft) x ( 1/Initial R-value - 1/Final R-value ) x 24 x HDDZ x Cost/Unit of Heating Fuel / Btu/Unit of Heating Fuel / Heating System Efficiency = Annual Dollars Saved)
We have to document a measurement don’t we?
Is this really our job?
No, but we are ready to make recommendations based upon… :?:
Did a web search for attic venting and this NACHI thread came up.
Myth Two is that attics need to have lots of ventilation. Again, venting requirements are not based on rigorous scientific research.
TenWolde explains that attic venting originally arose as a moisture-control strategy for cold climates. Other purported benefits, such as longevity of the shingles, arose later. It is widely believed that increased attic venting will prolong the life of roofing shingles by cooling them. But research shows that venting has very little, if any, effect on shingle temperature. The most important issue in shingle temperature appears to be the color of the shingles. Light-colored shingles reflect sunlight and don’t get as hot as dark shingles.
One possible real benefit of attic venting in climates with large snowfalls is to reduce snow melt on the roof to avoid the formation of ice dams. But according to TenWolde, a more effective——and energy-efficient——way to control snow melt in almost all climates in the United States would be to use air barriers and insulation to prevent heat from entering the attic.
“Mr and Mrs Smith bought this beautiful home in the burbs…it’s their first home, baby on the way, and were soo excited. They hired Mr Inspector because of his credentials and his expertise to evaluate the condition of this home.”
Their adorable cap cod was built in 1966! After 45 years, …I repeat your Honor…after 45 years their attic still looked like new! You can even see it in their inspection report…However, Mr Inspector insisted that it was necessary for them to close their gable vents. Wanting to do everything correctly, and not jeopardize their investment, they did so! A year later when they decide to hire a contractor to remodel their bathroom and install a bathroom fan, Mr contractor discovered the north side blackened from mold. Now my client is finding himself with a 10K estimate from a roofer with a written report that vents should never have been closed, sheathing needs replacement, and the now 6 year old shingles will have to be torn off."
Right or wrong about venting…how do you go about a defense?!
Yes sir, I mention the micro manometer which measures pressure differentials associated with temperature induced stack effect.
A much less costly device would be a cigarette or a stick of incense.
These devices are still used in weatherization analysis today. In spite of all the technological abilities of certain equipment, the ultimate goal is to determine what is actually going on.
If you use the primary rules (or laws of physics and thermodynamics) you can make an assessment without the thousands of dollars of equipment we are using here.
#1 hot air rises, cold air falls #2 for air to move from one space to another there must be an opening #3 in order for air to pass through that opening there must be a differential of pressure #4 the volume of convection is relative to temperature differential and vertical rise #5 in a closed system, air will not pass from one side of an opening to another unless there is another hole to allow the volume of escaping air to reenter the space from another location
Visually monitoring the airflow with smoke and considering these requirements will allow you to make a significant visual assessment of what’s going on.
Yes…you can get a PE,…but give a Website…are you kidding?
But just like any profession, you can have varying opinions both using physics and science. I’ve worked with PEs for 20 years and they have more opinions than a group of housewives. When I studied engineering, in “Products Liability” I had the fortunate opportunity to listen to a case on a guy who lost his hand in a machinery accident on equipment with a “two hand no tie down”. Both expert witness’s had opposite views on circuit design. Not one “single” answer fits every situation, and it’s narrow minded to think so.
It’s very interesting on what home inspectors hold as a source of un-disputable facts.
I’m not trying to pick on This Old House. I grew up one town away from this crew. When I moved to Tennessee I actually showed up to a home inspection with Norm Abrams’ Truck in the driveway! I worked for a mechanical engineering firm that did consultation work for this producer. I had to drive past the barns and homes that This Old House renovated in Carlisle, Ma. everyday on my way to Flir/ITC thermal imaging training. I am more than familiar with these guys. We’ve had more than one discussion in the past.
I didn’t particularly like Bob, but he’s in the past now. As I will soon be, you lucky guys!
You all have been in hot attics. As you move through the attic performing the inspection, there are times when certain areas of the attic feel hotter than other areas. Or maybe you have done as I and using your infrared taking the temperature of various areas of the attic (when the sun is high and parts of the roof are NOT shaded) noticing a significant difference in the temperature. When nearer ventilation points, the temperatures will be cooler. I have also noticed that the temperatures in the attic are more even when the ventilation points are more evenly distributed across the soffit and roof line, regardless of the type of ventilation. Therefore I tend to agree with Michael, if only gable vents are installed, air circulation is not even, and therefore not of best design.
As to David’s point on A/C’s in the attic in the south, I agree totally with ‘stupid on stupid’. We recommend approximately 12 inches of insulation in the attic to prevent heat transfer into the home, and place and HVAC in the attic with 3/4" of insulation inside the unit and duct work with a whopping 1" of insulation. Talk about going ‘green and saving energy’. Some improvements could be made here.
And by the way, there is more than one way to get A/C to another room, just check out the attached photo.
:roll:
I can’t display the pictures but I had an IAQ investigation that had the same thing on all the HVAC system. All the outside ducts were sprayed with Open cell foam. Any guess what might have happened?
I would only report defects and deficiencies.
Other than that it stays out of the report.
Not enough information to draw a hypotheses and enter it into a report.
LMO.
Same concept if you have a hole halfway down your tailpipe. The hole creates a type of back pressure on the system and interferes with optimum performance.
Around here Maximum type roof vents are used for most parts and installation instructions recommend blocking gable vents so as to promote air intake from soffits. It would be same principle for ridge vents, block the gable vents and open the soffits for maximum efficiency.
Documented research is on their website (below).
· **Improve: **When a Maximum type roof ventilator is installed, other roof/gable vents be sealed. More info at: http://www.ventilation-maximum.com/
I recently had my roof replaced. I have bird block vents below the eave (exposed rafters). The roofer added intake vents a couple of feet up from the edge of the roof as the bird block vents did not provide enough ventilation. I’m wondering if instead he should have increased the number of bird block vents?
Does mixing intake vents (two feet from eave) with bird block vents short circuit the ventilation? Thanks in advance for your input.
