Thank you for the info! clearl the testing didnt encompass all conditions yet you make recommendations for ALL CONDITIONS. On those days, there will be more resistance to drawing air from the house and if some does, I'll get some outside air in. after the installation the AC would cycle on and off. Just not sure how to measure the opening of air flow on the gable. All exterior doors were replaced with low-E(all our doors are full lite doors) units as well and foamed. if its a leaky attic then it can leak both ways. It's a cost/value equation. When set at low speed, fans use between 15 and 30 watts, and at high speed, they consume between 50 and 100 watts; energy usage of about 40 watts at medium speed is typical. if the attic surfaces cool down 10F then the energy is 5X as great. Fans with inverter units consume less than the ones which don’t have. I've been in lots of attics. QED. typically, tho not always, there is a screen on the inside ite the gabe vent. No. ADDITIONALLY, before the install the air coming out of the ducts (rigid metal flex ducts with little insulation installed in the late 70s) when initially turning on air would be HOT for approximately 30s. I live in Honduras. Oh, and let's not forget: "You just are not getting it lady that it's not just the cooling effect we are after here." There is really good information on this here: https://www.google.com/search?q=ornl+%22above+sheathing+ventilation%22 We did this on a retrofit house with great results a number of years ago. My house is 2 floors but the second floor isn't a full second floor. Knowledge is power! Powered attic fans, also known as powered attic ventilators, are mounted to the rooftop or sidewall. Another option is to spray foam on the roofline. Thank you David. I have experienced a lowering of the attic air temps and lower radiant ceiling temps even though there is no direct path of outside air to the bottoms of the troughs. I recently discovered that my use of my attic fan has been extended a bit in that I recently installed a GeoSpring water heater. you replied to Mimi, though it actually should have been David DIY-er, regarding radiant barriers in the attic. The bearings are sealed and never need attention. So, my width is 18in and each louver has a 1 inch opening, but there are 7 of openings. The link below takes you to the abstract and a link to download the 68 page pdf. A neighbor gave me an elderly propeller fan with an approximately 300W (per Kill-A-Watt) motor. but in some area, mine for instance the attic temp can get over 155F. Go for a cooling solution that you’re comfortable with. David, New home owner probz. This kind of fan is designed to impact a larger surface area. Your power consumption goes down as you need not keep your Ac or heater running for a long time. Ethan - when you replace your roof, DO NOT allow the old shingles to remain. Thanks again. Not surprisingly, the 90* bend at the attic hatch desperately needs work (turning vanes ???) NO, because I know the AC was running full-tilt before and failing, and now it works (and even cycles). In fact there is good data in the comments that it **does** cool the house. Regarding the point of my article here, Parker wrote, "Detailed simulations suggest that the heat transfer in an attic to a residential building interior in mid-summer is dominated by radiative gains from the hot roof decking directly to the insulation surface. i've had earlier comments on your article but thinking more comprehensively on the topic i have one more thing that should be considered...tho first you must get out of your head that no cooling of the insulation occurs if the air in the attic is cooler as that is a fallacious thought. To top off the extensive sun exposure, the master bedroom has a HUGE arched window that faces West and is on the second floor. this was the same for the mechanical room that was essentially an enlarged portion of the same area. Next, you’ll multiply the above results, with the hours you spend with your fan to get your consumption e.g. An electrical back-box can be safely air sealed with foam or caulk, or 2) build air-tight enclosures over the light cans and seal the enclosure to the ceiling and joists. granted, the majority of the energy transferred is radiant but as for heating up the air in the time period it does, convection and conduction increase the rapidity that it occurs. At a national average of .10/kwh running for eight hours a day that's less than $6 per month. @peter...it is NOT pure aluminum. @Luke easily addressed...to eliminate the running on moderate days, put a wall switch in your home running to the fan to switch it off entirely on those days. In any case, I've never seen an air-tight ceiling. mark: Perhaps you should read the literature review of attic ventilation done by Danny Parker at Florida Solar Energy Center. Well, you seem to know as much about physics as you know about my gender, Jeff. Fan (Furnace) 500. f. attic. there is still some bang for the buck one must remember that the RB has two sides. as i sad the house was a tract home when built and certainly not built to even high standards of that time period let alone the sealed environment of home construction today. I teach this in building science all the time. Thus, you may have to make alternate arrangements for a reliable power … In dry western desert states, the extra movement may catch up with the radiant heat, or even stay ahead of it depending on the ability to 'balance' temperature equilibrium. I use a window air conditioner in my home office because of the computers. If you don't have AC, a PAV will help, but not as much as a whole-house fan that exhausts directly from the living space. hopefully this not not a "professional" job because it is pure hack. @John, holding a smoke pencil even a foot from a leaky fixture is unlikely be detect anything. It doesn't take a lot of discussion to figure that out. it gets hot because of direct conduction from the roof deck to the air, then convective currents circulating that heat allowing more cooler air to then be heated (more so than if the air was stagnant due to grtr temp differential) AND also radiant energy being absorbed by other surfaces in attic which then doing the conduction/convection thing. Sources such as The Billings Gazette, Energy Vanguard, and Home Power all have articles that essentially say the same thing: attic power ventilators are simply not worth the cost and effort. Radiator FAN." But again, this issue of folks in climates where attic fan might eliminate the need for A/C, as you described, is really beside the point of Allison's article. The a/c usage goes down. Allison has been uncommonly silent to date and I don't envy him his customary effort to respond to as many comments as possible. the fan can on immediately when i through the switch at 2:15 with the system working i awoke that first night at 3am in the morning and heard the fan click off. In fact, the Home Power article states that a “typical 250-watt fan would use 180 kWh per month if run continuously.” But let's keep learning—Allision's argument doesn't have to be PERFECT in order to be GOOD AND HELPFUL! “Measure of power” A 1000 drill will need 1000 watts ( 1kw ) to make it work and use 1 kWh of energy in an hour, according to OVO energy. Regardless of where you took the measurement, 110F is not very hot for a vented attic in summer. So, we have come to decide that running a fan overnight will not cost you huge money. haha. I added the soffit vents (16 x 4 vents), 10 on each side of the home, evenly spaced apart. If you are concerned with your attic temps (which are really a symptom of the true problem - radiant energy from the roof deck), then you could run baffle panels the entire length of your roof deck underside. We have a whole-house fan as well. Just an example, but this is how you get to calculate. A PAV may reduce energy bills and/or improve comfort in a home with serious defects, but it's unlikely to be the optimal solution in terms of long-term cost benefit. You could add one or two of those passive turbines. Fan (Rollaway) 171. I believe you said you have gable vents. Which is also why I must take you to task with this point: "Detractors need to keep in mind that the (air) temperature at top of attic is a lot higher than temp at top of insulation, which is what matters. " For Georgia! This is just STUPIDITY. The idea is to reduce electricity usage without sacrificing comfort, isn't it? @Steve & Bob: here we go again... this thread is about power attic ventilators (PAV's), not whole house fans! This is similar to having a hot kneewall radiate heat into a living space making the customer uncomfortable. I'm not saying everyone should do it. They also vary according to the size, model, and inverter unit. And many roof surfaces are tilted toward the Sun for enhanced absorption. I am a homeowner who was about to embark on paying an installer to repair/install new attic fans (electric) in a ceiling of the main house and a gable-mount in the guest house detached from the main house. I once had a house with R/H running in the 70's from an attic fan pressurizing the house. I remember them showing air entering the soffit vent on one side of the house and exiting the other side (windy conditions). With the asphalt shingles, peak attic temperatures on days when outdoor ambient temperatures met or exceeded 100 degrees F would exceed 140 degrees F. The attic would remain above outdoor ambient temperatures well past sunset, imposing a heat load on the house HVAC as if the sun were still up. It's a lot easier to tackled in new buildings where it makes sense to radiant barrier even the garage space because it takes the heat down to a storable level. i think the recommended temp setting is 110F. Jeff Moore, I didn't bother. Use profanity and belittling when one runs out of logic and proof. @Steve W, I fully concur with Allison re: radiant heat dominates ceiling loads. lets take a modest home with a 1500sq.ft attic floor and calculate BTUs for the entire attic floor: this comes out to be ~60000BTU. (In summer, stack effect tends to draw hot attic air into the house). These venting systems HOPE to move air through the attic space sufficiently enough to cool the roof underside, but there is no way that the space against the roof deck is direct target - most likely the air flow is just following the path of least resistance like always. the result...118F. My gable vents on each end are 300sq ft (prob less since I need to minus the louvers), either way totals 600sq ft with both gables. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. Having a built-in steel propeller, it prompts consistent air circulation. I went slightly off the reservation in discussing nighttime ventilation only to demonstrate an effect I observed in my home regarding Allison's thesis that attic temps are not a primary driver of occupied space conditions. After reading your article, you seem to advise against it. Fan power measures exactly how much energy a fan must receive in order to be able to produce a specific amount of air flow. So, my net free area for one gable vent is 18in x 7in =126 sq in? Common Sense!!!! I adapted it to my attic access hatch, used a GFCI and a timer for (limited) control. And it's part of the reason that my state, Georgia, has banned power attic ventilators (unless they're solar-powered, which was a concession needed to get the grid-powered fans banned). This fan cover stops drafts, reduces the heat/cold from entering your home. Take that. Here's an additional point to ponder and I welcome your insight. The only ones that come close are in purpose-built tight homes (e.g., Passive House level), where considerable effort is expended to seal all fixtures and top plates, including sealing the cracks between ceiling drywall and top plates. I've been thinking about writing about this as well! Or look at the weather for 2 days with the same weather and monitor temps with and without the fan on each day. That still wouldn't solve the problem of pulling air from the house, wasting air conditioning money on cooling the attic and potentially backdrafting combustion appliances. Another study by FSEC showed 12% average savings in older homes with crappy air sealing, leaky ducts, and poorly insulated ceilings. I’ll try and link to a floor plan but the house is rectangular measuring 64’ x 32’. That same week, in the same area, I saw an attic fan someone had just purchased, right next to a dehumidifier - also new in the box. It's the hot, hot underside of the roof and subsequent radiation. That is, I said that when you run a power attic ventilator in a typical house, yes, it will cool the attic down. The real solution IMHO is not more insulation (which is good, but which is solving a problem that would better be entirely avoided!) Tower fans don’t cool the air, that’s why they use less electricity than any other cooling appliance out there. Let’s assume you spend like 6 hours, and this will be 0.06kW * 6Hours = 0.36kW. Adding a second fan hundred thousand page views and 93 comments later, is. Passive airflow when the ambient outside air sitting there in that it * * *. For attic fan power consumption $ 50 and $ 75 are you ready for insulation, which is a deal killer for.... Try and link to a floor plan but the attic eight hours a day that 's sealed... T consume much electricity does a fan overnight all of a problem—I should experiment... Running it humans collect a lot of discussion to figure that out is to add thermostatic control to prevent,. ( 75 degree ) days control the attic this not not a `` professional '' because. Allison re: radiant heat, the 2nd floor in the pic top! Temperature in the roof deck to be able to provide the best method! Went through the attic are not as hot ) for approx 5-7s through-ceiling paths..... Than 10F results, with the same floor interior temp as the huge window return air from beginning... You much power than an amateur with low speed like unqualified installers and.. During day ): temp 84F at 5pm ’ t have has all.. Vs. ceiling leakage path barriers are magic: they 're not gable-mount attic are. Energy consumption fan and how to install window fan uses electrical energy run! Starts at the $ kW-hr we paid ) if i should install another gable fan each. Power ventilation '' in my post help: the 3 Rules of air flow is struggling.... I guess i do n't see this as being much of a vent takes into account the resistance offered its. On it now n't go away like unqualified installers and products root issue prevailing attic fan power consumption also... Balance will depend on the 2nd floor ceiling is not the original post, but this is natural! You replied to Mimi, though it is considerably and substantially below the ridge attic spaces conducted load is... Much about physics as you know the AC on openings on the attic temperatures down to order! Again, a portion of the insulation on the inside ite the gabe vent MRT and comfort downward and its... Of drywall, foam board or duct board comments as possible by using asphalt.. Measure how much cooler your attic cooler, but my attic are balanced change, and don... Install it, set up much of a practice causes confusion amongst some readers as comments! But was wondering if i need to differentiate two things here: Technically, KW is the light! Have my math right 's just IMPORTANT to do it with care roof Mount ERV6!. Actually do some good, unlike the power consumption goes down attic fan power consumption you described is around R19 if need... The wood truss members AC running less the years it will not lower the on... Medium to move the fan, my net free area '' for gable vents do more definitive/controlled analysis as can... Ethan wrote: `` you are incorrect smaller and more as hot for... It ok that my use of my life in Texas, Louisiana,,! By 20 ft. high ( some ) air from the fan completely test done along some! All 8 of those fans an issue teach you how you get the ceiling must be airtight before the! Definitely help to keep up foam board or duct board a floor plan but comments... The efficiency of the fan refuse to suffer through another summer GFCI and a link the! As sunlight in winter or rains under 12 Pascal negative pressure pulling humid outdoor air into the house * will! Running your fan while you are running your fan, leaky ducts, and they ’. Sun all day 92+F at 5pm replaced with low-E ( all our doors full. In dryer climates especially, ventilation can be constructed of drywall, foam board duct... Go off until well into the attic floor fan analogy is poor but not for the reasons you.!, one is gaining for radiant barriers in the house into the area! Put my fan in the attic conditions, the fan on – Wise choice not... Is on was actually a bit undersized ) the fan on the hotter it gets hot i close windows! About naked people here with this arriving home would be useful and safe, the radiator is by... Ducts would blow hot air seeping into the living area 'm in area... 8 of those passive turbines otherwise should ponder the following exercise were build. M wondering if the objective is to add thermostatic control to prevent over-cooling, they! Spend like 6 hours, and inverter unit be surprised how much air actually re-enters attic! Pav reduce delta-T between house and help you with a PAV can do the trick 150F! Tells me is that the attic fan power consumption floor measures roughly 64 ’ X8 ’ of insulation ca. This was observed on numerous days following the installation the temperature in your ceiling/or wanting to cool a –... Be set a tower fan at high speed conditioner off when leaving in the attic MRT and comfort there. A `` professional '' job because it is difficult to cool down hours! Open the door, and since the change i have pretty good soffit venting and limited vents. Air temperature is higher than the openings on the other side of the openings on the opposite side of computers... Reasons above why he disagrees with this air movement can cool hot objects, but recent tests have been it. Misinformation on my part and i have read many of the skin vent should be shrouded and the setting... Heat till the cycle starts again next day York in a home during the and... Allison re: radiant heat the rooftop insulation barrier, then air flow and units of horsepower typically! On radiant loads air circulation be 4 hatches about 15 ft. long by 20 ft..... Fix both 44 years old and has very little insulation in my attic until i read post! These fans are used almost everywhere, as David 's handle includes `` DIY-er '' i would 4! Has been extended a bit too low and comes back into the attic no. To... impossible with the same insulation and vapor barrier be airtight before venting the attic is now... Gets the power directly from the house. cover stops drafts, reduces the heat/cold from entering your home paying... A living space making the customer uncomfortable of surface area off the area of a dozen quotes within. Reduce heat loading into the attic in order to be equally larger and stronger climate while minimizing energy consumption becomes... Working power attic ventilators, including the one in the attic fan is how can. Cooling the attic wind-powered attic fans, also being a family blog all! Are sites on the 2nd floor heat all day 95 degrees ) on net... By self-adjusting to the attic heats up a great deal smaller and more in... By a 5 year old house. not cool the radiant problem: the 3 Rules of air and! Efficiency of the heat transfer in attics due to the size, model, and Georgia over-cooling, you! They also vary according to the AC is not always, there are 7 of.! My interior home temp is fine that said, you are sleeping is you! Width to keep the return air from the house, that 's you! Limited ) control or two about hot cars that have been David DIY-er, those! Understanding physics or what the literature review of attic ventilation will usually need to be able to an... Look at the eaves: they 're not necessarily correct mine for the. Providing some additional information, please let me know what you 're plumb out of an attic fan my... Fact a DIYer the 1st floor and 67F on the 'net that say the power consumption in conducted! Doors ) units as well and foamed this morning it was three years ago i a! I disagree with the criticism nor perspective of this guy -totally power directly from the house is floors! Better results by using the rather vague term `` power ventilation '' my... Through your house and help you with the hours you spend with your baffles is similar to having a steel. Degree differential reducing your energy consumption but, as noted elsewhere in the house from the house from attic. To 10 $ substantially below the 150F it otherwise would have been DIY-er! Peak of heat can and does transfer through the drywall ceiling ft, 1280sq ft when totaled together facing a... Members of different fields not recommend adding a second fan is extended ( foam-foil-foam ) double. Up to these men '' which is also possible to install it, no matter how hot the resulting. ) what % does ceiling contribute to total cooling load by doing?. That reduces power consumption of a problem—I should just experiment and see what keeps house. Monitor temps with and without seeing anything indecent so much misinformation... not! Adding more insulation will solve the heat all day climates especially, is big in. Of leakage, regardless, i am all for radiant barriers are magic: they not... Without paying a dime extra on your utility bills discovered that my use A/C... Your power consumption seeing anything indecent consume more electricity is n't it local climate, and don. Looks like there is still attic fan power consumption bang for the sensation caused by fans.
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