About jeffatha

Nov. 23, 2008
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  • jeffatha commented on Phil B's instructable Make Center Drilling of a Rod Easy9 months ago
  • jeffatha commented on More Cowbell's instructable Air Seal Your Attic For Energy Savings9 months ago
    Air Seal Your Attic For Energy Savings

    As an addendum to my original posting. In regards to the net free air exchange rate:Some well meaning home builders, contractors, and home owners will install powered attic exhaust fans to augment the net free air exchange rate. This is a good idea which can quickly backfire if not calculated, and implemented properly. As mentioned previously, there is a specific formula to calculate the appropriate net free air exchange rate for a building, "net free air" meaning the total volume of naturally free flowing air into and out of the attic space. A powered attic exhaust fan will increase the exhaust rate of the air pulled from the attic space. However if the volume of air coming into the attic is less than what is being exhausted, a vacuum condition may develop in the attic space. The volume of air exhausted from the attic space must be equal to or less than the volume of air capable of coming in through other vents. Therefore make sure all soffit vents have unimpeded air flow!So why is this important? A vacuum condition in the attic space can pull air from the living space, thus in part, transfer a portion of that vacuum to the living space. Combustion exhaust gasses can be pulled into the attic from leaky exhaust flues, and/or more importantly, directly from combustion sources into the LIVING SPACE! Combustion exhaust gases can come from various sources, such as, wood or gas fired fireplaces, wood or gas fired stoves, wood or gas fired water heaters, wood or gas fired heaters (space or central), gas fired clothes dryers, or even from an engine running in the garage.From a safety and health perspective, any building with combustion source inside may be well advised to have a free flowing source of fresh air coming into the building from the outside. Breathing combustion gasses is harmful to health, and can cause carbon monoxide poisoning, and even death. To be optimally effective, a powered attic exhaust fan should be installed at the highest level possible (because heat rises), and away from any other naturally free flowing vents. Optimally a powered attic exhaust vent should only pull air into the attic from soffit vents, or any other vent specifically placed to bathe the bottom of the roof deck with its air flow. As a recommendation, only install a powered attic exhaust fan that has a temperature sensor and switch designed to turn the fan on/off at a predetermined attic temperature. Optimally this temperature sensor and switch should be adjustable. Furthermore as a convenience, a switch could also be installed outside and near the attic entry to easily control power to the fan. Hope this helps!Sent from my iPhoneSent from my iPhone

    Sherri,As a rule of thumb, nothing electrical should be covered with insulation without specifically being designed by the manufacturer to be covered with insulation, especially cellulose (paper) based insulation.I think you have good intuition to suspect a possibly hazardous situation. IMHO, giving the type of advice you are asking for would be foolhardy without actually being there. So I HIGHLY recommend asking one of your city's building inspectors to go out to your home and have a HANDS ON look at your specific situation.Furthermore, I do not recommend asking local builders, contractors, or property appraisers, etc, because the likelyhood you may not be taken seriously since you are female. Much like a female trying to discuss engine problems with an auto mechanic, unfortunately she probably wouldnt be taken seriously. Sad but true. Hope this helps, and good luck.

    Oops! 144 - 8 is 136, not 95. Don't know how that typo occurred. Sorry! So the installer would have underestimated by 135" inches.

    There are several problems with the original posting as well as some of the comments. So in no specific order:1) Do not use METAL or anything else to seal the air gap around the chimney flue, unless the seal is specifically designed for that purpose. That air gap is there to prevent heat transfer from the flue to the surrounding materials, and thus reduce the likely hood of spontaneous ignition. Metal, more so than other building materials will readily conduct the heat from the chimney flue to any material it touches. 2) Do not vent any exhaust fan to the soffit vent. Soffit vents are for air intake into the attic ONLY. All exhaust fans should be vented out to the exterior, otherwise anything in the exhaust can, and most likely will buildup on attic surfaces. This includes not only bathroom vent fans (fart fans), but more importantly kitchen vents due to the grease content of the exhaust. 3) There is an exact calculation to determine the ratio of soffit (intake) venting to roof (exhaust) venting. The calculation takes into consideration the "footprint" of the attic and the pitch of the roof to determine the "net free air" exchange rate. The air in any attic space should be dynamic, and freely exchange with the outside air. Counterintuitively, the attic air should be as close to the outside air as possible, otherwise moisture and mold can become a problem, and ice dams can form above the soffits in the winter. Furthermore if the exchange rate is low during the summer allowing the attic air temperature to rise, any insulation on top of the ceiling will act as a heating blanket at night. The take-away here is to ensure the air exchange rate for your attic has been specifically calculated and implemented for YOUR specific house. 4) Radiant heat barriers installed under the roof decking and joists can, and most likely will cause premature failure of roofing shingles. This happens because the heat that is normally radiated into the attic space is reflected back at the underside of the roof decking. This increases the temperature of the roof decking, which will in turn will radiate the heat back to the bottom of the roof shingles. If roof shingles become too hot, the manufacturer installed adhesive on the backs of the shingles will prematurely fail, the color texturing will begin to come off, and finally the edges of the shingles will curl. This failure can be exacerbated in areas with high winds, because the shingles will begin to blow off due to the failure of the adhesive. If you read the manufacturers warranty for roof shingles, the are specifics to the limitations of the shingles, and the liabilities of the manufacturer. 5) Install attic insulation according to EPA and DOE recommendations for your geographic location. By U.S. regulation, every new home must have a series of insulation depth markers installed in the attic to indicate to potential home buyers the depth of the insulation. Unfortunately building inspectors and code officials rarely enforce this. As a matter of my personal experience; unfortunately much of the information I have provided here is completely or in part unknown to builders and contractors, or is simply dismissed due to financial incentives. If you have any doubts, please do the research on your own. Also have a look at the building codes for your area. Good luck!

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