Solar attic fan - worth it?

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Has anyone put in a solar attic fan? I have a two-story house with a separate A/C unit for the upstairs and downstairs. The downstairs A/C runs fine and keeps that area cool without any problems. On the other hand, the upstairs A/C struggles to keep the area cool throughout most of the summer. I'm attributing a lot of it's struggles to the hot attic above the air space it is trying to cool. I've read up a little on solar attic fans and it seems like this could be very useful for reducing the air temp of my attic by a good 15-20 degrees in the heat of the summer. In turn, I'm assuming this will assist my upstairs A/C with keeping the air space cool. Has anyone had any experience with solar attic fans?

Thanks in advance.

Trey
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: Solar attic fan - worth it?

    From what I've seen/heard, most of the solar attic fans are a joke. I think the rotary turbine cap is the better way to suck heat out of the attic, and you seal them off with a trash bag in the winter time.
    The other likelyhood is that the upper AC unit, creates lots of cold air, which rolls down the stairs, and keeps the lower level cool.
    Try some reflective insulation on the 2nd floor ceiling, vent the attic (inlet & outlet)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Solar attic fan - worth it?

    proper ventilation for an attic even in winter is vital. you don't want any trash bags on them or blocked in any way. this keeps condensation down which could negate some insulations and damage the roof. venting this also helps somewhat to rid the attic area of heat during the summer and i agree that the rotary caps may be the best way to go, but do be sure you have free flows of air from lower levels of the roof or it will stagnate the air and thusly the heat of summer and condensation in winter.

    i think the answer may be to put both ac units upstairs and let some of it escape to the lower level. i do this at my place and it works for me, but i have more than just a stairway to allow airflow between the floors too. this takes advantage of the fact that hot air rises and cold air sinks. your lower level ac isn't working hard at all because some of the 1st floor heat has gone up to the upper floor and some of the cold air from the upper level has sunk. this is in addition to possible heat infiltration from the attic area that makes the upper ac unit work even harder. if you must have ac on both floors then go with a small unit on the bottom floor and a larger one above.

    another overlooked problem could be air leaks. when air is allowed to pass on upper and lower levels to the outside this makes the house colder in the winter and hotter in the summer and can be worse than a home with less insulation, but is sealed.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Solar attic fan - worth it?

    A good attic ventilation system will have intake vents in the soffits, and exhaust vents at or near the ridge, with a healthy airflow space ABOVE the insulation to allow convection to create a flow. The UBC has formulae for the square ft required of intake and exhaust per sq/ft of attic.

    Having the UBC minimum may not be enough in the summer, and may indeed be too much in the winter. (I have attended several insulation/venting construction seminars on the subject, and there is considerable info available).

    The biggest problem is the efficiency of the insulation AND vapor barrier. In the winter, the warm air of the house, cools as it passes through the insulation, and at some point reaches the dew point and condenses. A proper vapor barrier significantly reduces the AMOUNT of moister that can condense, and therefore needs to be vented. The problem in the winter is frost forming on the underside of the roof deck. Venting won't always remove it, as some of the moisture can enter through the vents! Once report I read once said " If you look up at the roof deck and see frost and you have no venting, add some. If you have venting and see frost, close it!"

    In the summer, there is really no such thing as too much venting. If youa re trying to keep your a/c costs down, (assuming you have maxxed your attic insulation first!) adding gable end vents, ridge vents, or fan forced vents, (good solar ones are available) will keep the attic temp down and reduce a/c costs.

    An even better way to keep the attic cool is to keep the sun off it! Plant trees!

    Good luck,

    Icarus
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    Re: Solar attic fan - worth it?
    icarus wrote: »

    An even better way to keep the attic cool is to keep the sun off it! Plant trees!

    Or cover it with PV cells
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • sawmill
    sawmill Solar Expert Posts: 93 ✭✭✭
    #6
    Re: Solar attic fan - worth it?

    I also have a two story house with separate heat pumps for the top and bottom. Two years ago I installed a 10 watt solar attic vent and could not be happier with the results.

    Since the installation we have not had to use the upstairs ac unit but have had to use the downstairs unit for many days at a time here in the mtns. of NC. Of course your climate would have different requirements. I don't want to imply that a 10 watt vent will take the place of AC, but our results have been good.

    I used a thermostat so the fan does not exhaust in the winter, but of course there is still natural venting through the fan opening. I can tell no difference in heating the upstairs bedroom during the winter.

    Anytime you can reduce your attic (oven) temperature during the summer and increase air flow is a good thing.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Solar attic fan - worth it?

    On an earlier attic fan thread here (actually post is here), I remember reading a post, where after several years, their attic fan failed and they did not even notice. Just adding the extra ventilation (from installing the solar powered attic fan) was enough to reduce their attic temperatures...

    Regarding adding solar PV panels to the roof--On my house, adding the panels reduced my attic temperature a lot... Of course, just adding a fan would have been cheaper than a PV roof shade. :p

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Telco
    Telco Solar Expert Posts: 201 ✭✭✭✭✭
    #8
    Re: Solar attic fan - worth it?

    Hey, this might help. This guy seems to be all about measurements, a lot of the stuff he'd done he apparently does himself when possible and he measures everything. His hot water setup has more dials, gauges and switches than a submarine. Looks like he installed one and saw a 20-30 degree drop in attic temps, which reduced the amount of time the AC has to run in his upstairs office. I've found this site very interesting if you go all the way to the beginning, as he details installing a solar water heater for home/office heating and lists the problems and fixes along the way.

    While it is very possible to vent naturally, a powered vent can overcome a lot of shortcomings in the existing structure much like a supercharger can overcome a lot of shortcomings in an engine's intake manifold design.
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  • lamplight
    lamplight Solar Expert Posts: 368 ✭✭✭✭✭✭
    #9
    Re: Solar attic fan - worth it?

    the article BB quoted was something i started last summer I think. I put a 12v radiator fan (mucho cfm's!!) that crewzer found in one of my gable vents pulling air out, I have it on a 12hr wind up switch for hot days i do it manually. it helps for sure, as do (as someone said) the solar panels that have since been added to the roof :)

    the radiator fan was cheap but pulls quite a few amps, and is loud (not an issue here), and also it uses my existing solar 12v - so if i didnt have that i would have considered a quality $300 solar attic vent a relatively cheap investment. i think with properly vented/constructed homes (or if you have the money to do that as retrofit) natural convection should be adequate.
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  • kc8adu
    kc8adu Solar Expert Posts: 50 ✭✭✭
    #10
    Re: Solar attic fan - worth it?

    i have seen temp drops of 30-40 f from covering the south facing roof of a neighbors house with pv.
    they measured temps for a week before the install because they did not believe me when i told them the attic temp would drop.
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  • dale
    dale Solar Expert Posts: 29 ✭
    #11
    Re: Solar attic fan - worth it?

    The benefits of dropping the attic temperature in the summer are obvious. If PV lowers the temperature in the summer would it add to heating cost, or freezing, in the winter?

    As Icarus said, cold air fall and hot air rises. It would seem that you'd want a higher powered AC on the second floor and lower powered for the first.

    Insulation always helps. People rarely consider the effect of shingles. I think all new ones have a reflective quality, but I'm not sure how it is rated. I heard that it increases the life, but don't know if that means 30 yr is more reflective than 15 yr ones.

    I do know that after replacing hot (black) tar roof, the house was noticeably cooler. This might be worth investigating if you re-roof.
    Good luck,
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  • Telco
    Telco Solar Expert Posts: 201 ✭✭✭✭✭
    #12
    Re: Solar attic fan - worth it?
    dale wrote: »
    If PV lowers the temperature in the summer would it add to heating cost, or freezing, in the winter?

    Nope, the fan doesn't run in the winter if it's thermostat controlled (which you want anyway), and you can block the hole off provided the vents aren't 40 feet over rafters as in my house. Course in my last house I didn't bother blocking the vent in the winter and didn't see any noticeable increase in BTUs on my gas bill, just an ever increasing bill due to cost per therm.
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  • dale
    dale Solar Expert Posts: 29 ✭
    #13
    Re: Solar attic fan - worth it?

    I'm going to think about that. Haven't had time to go through it yet, but the arttec link looks good. Thanks.
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  • System2
    System2 Posts: 6,290 admin
    #14
    Re: Solar attic fan - worth it?

    I have just had an electric attic fan installed in my roof and since finding out about these solar versions am considering swapping it out.
    I just have a fairly standard bungalow. The insulation in the ceiling is adequate but not up to modern standards. I have 2 gable vents installed to allow air flow through the attic.
    At the moment the electric fan is a 1250cfm unit. Should I replace it with a 20W solar unit?
    Is there much to choose between the different units.
    There seems to be too main choices. Either the natural light fan or the sunrise solar unit. The natural light one seems to have the best warranty and is all made of metal. I saw the sunrise unit which is black and plastic.
    Any comments about which to get if any?
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  • System2
    System2 Posts: 6,290 admin
    #15
    Re: Solar attic fan - worth it?
    whs9841 wrote: »
    Has anyone put in a solar attic fan? I have a two-story house with a separate A/C unit for the upstairs and downstairs. The downstairs A/C runs fine and keeps that area cool without any problems. On the other hand, the upstairs A/C struggles to keep the area cool throughout most of the summer. I'm attributing a lot of it's struggles to the hot attic above the air space it is trying to cool. I've read up a little on solar attic fans and it seems like this could be very useful for reducing the air temp of my attic by a good 15-20 degrees in the heat of the summer. In turn, I'm assuming this will assist my upstairs A/C with keeping the air space cool. Has anyone had any experience with solar attic fans?

    Thanks in advance.

    Trey



    As long as your solar attic fan has a rated CFM = (attic volume x 10)/60

    You should be able to cool your attic to 5-10 degrees above the outside temperature. Depending on your insulation. This should make your ACs considerably more efficient.

    Good luck!
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  • System2
    System2 Posts: 6,290 admin
    #16
    Re: Solar attic fan - worth it?

    I have a similar question and this is outside the box for most of you. I live in Tucson AZ. High heat low humidity. We don't have the problems with condensation that others would have.

    When i was building houses 10 years ago insulation was at the drywall ceiling (for flat and sloping roofs -- most roofs slope no more than 4/12 my house is 3/12) and then you vent the roof. When I went to build my new house a year ago, the architect insulated the top of the roof and did not vent the roof at all. This seems to be the prefered method of insulation in Tucson -- but it seems counter intuitive.

    Heating bills in Tucson are a much bigger problem than cooling bills. So my thought was heat rises, creates an air pocket and that air pocket in its self is insulation. If there is a means for the air to escape than new air would replace it -- form the fastest source -- which could be the air below.

    I still think somethings wrong. I am thinking about insulating the top of the ceiling and having no venting. Any Thoughts. Sorrr so long winded.

    Thanks
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #17
    Re: Solar attic fan - worth it?

    if by you saying the architect in insulating the top of the roof means that just under the roof slope and inbetween the roof rafters is insulated and not on the top of your ceiling i think that is not good and it is not possible to vent as this would introduce outside air into the insulated zone with a possible exception(see below). this raises the insulated zone to the roof itself and not just your ceiling. this means a larger area to cool or heat as it is now part of the living space area to the roof line even if the condensation won't occur allowing such a practice. do you live in your attic area? if not then that architech is not good at what he does imho if i'm not misunderstanding anything. it also means more insulation would be needed than had the ceiling itself just been insulated as the roof would encompass a higher square foot area.
    exception can be had when using some urethane insulation boards as an air space could possibly be left between the roof and the insulation and only venting that space. this still would not change the fact the attic space (even if small) is now considered part of the living area thermally.
    in general venting methods used elsewhere could be appied to your area with good success as when the attic air is higher in temperature than the ambient (which it often would be during hot months) a free natural flow could take place by allowing the super heated air to escape and allow the cooler ambient air to replace it with even if that ambient is over 100 degrees f as it often is in arizona. this won't be possible if that area is included in the living space by insulating in the wrong place.
    maybe i'm getting the wrong picture in my mind's eye of the circumstance and if so please elaborate with further explanations as i might not be understanding what the architect has really done by your explanations.
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  • System2
    System2 Posts: 6,290 admin
    #18
    Re: Solar attic fan - worth it?

    It depends on the product.

    We used two AIR VENT SOLAR FANS and they haven't worked right since they were installed (by a professional roofer). They get full sun all day (northern exposure during the summer), but the fans barely spin. My attic is actually hotter now than it was before I had the fans installed.

    A service representative from LUCY & ASSOCIATES came by to inspect the problem and told me confidentially that the best solution is a standard heat release duct, or electrical fan. Apparently, even their own rep feels that AIR VENT SOLAR FANS SUCK, or more literally, don't suck (air).

    Moreover, although AIR VENT claims a 5-year warranty, they have already begun to put obstacles between themselves and resolving the problem.
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  • System2
    System2 Posts: 6,290 admin
    #19
    Re: Solar attic fan - worth it?

    I use one and I think it's well worth it.
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  • BillF
    BillF Solar Expert Posts: 48 ✭✭
    #20
    Re: Solar attic fan - worth it?

    I had four units (Natural Light 10 watt) installed this spring when we had our shingles replaced. We have a story and a half and noticed right away that the second floor was cooler. For us it was not only pulling heat out of the attic but also keeping the roof/wall area cooler by moving air through the channels between the rafters. Active ventilation seems much better than passive in this case.
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  • System2
    System2 Posts: 6,290 admin
    #21
    Re: Solar attic fan - worth it?

    I have acquired a number of 5W and 10W panels, and would like to use them to power a fan in the attic.... anyone know of a good source for just the fan? Seems like everyone wants to sell the fan/panel combos.
    Thanks!
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #22
    Re: Solar attic fan - worth it?
    John wrote: »
    I have acquired a number of 5W and 10W panels, and would like to use them to power a fan in the attic.... anyone know of a good source for just the fan? Seems like everyone wants to sell the fan/panel combos.
    Thanks!

    When I installed the gable end kits from Home Depot, the solar panel and fan were sold as separate units.

    One thing you might consider is that the reason they were sold as separate units was due to the fact that the fans could run on a single 10w panel, or you could hook up a second panel.

    So you might do well by buying a kit with fan and 10w panel and then boosting its performance by adding another panel from your collection.
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  • doohic
    doohic Registered Users Posts: 10 ✭
    #23
    Re: Solar attic fan - worth it?

    Does anyone know other solar/wind forums that are very active with highly knowledgeable members? And please no offense if I have found the right place!

    Now that it will start cooling down here in FL one of my 'winter' projects will commence. That includes putting in two gable style vents. AND I am planning on also using fans in each location using solar panels and I'd like them to be on a thermostat. (this is my very first solar project)

    I thought I would find more DIY set-ups here in the forum (although havnt looked to closely yet). I saw someone mentioned using an auto fan. But, I see most people are using kits or off the shelf products. I was hoping to find a very active and knowledgeable site that could offer some DIY solutions, what fans were most efficient to use, and what type of panels to use, etc.

    So, HI :) I am very interested to hear what you guys have to say. wow I need to change my settings.. i thought this was a really old thread when i started reading... newest post is first.. crazy.l
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #24
    Re: Solar attic fan - worth it?

    We have a little wind related stuff here--but there are other places that do wind better...

    www.otherpower.com
    www.builditsolar.com

    I, personally, am not a big fan of wind (few locations have enough wind and open land for a practical installation)... Here are some other links about wind from other threads:

    Wind Power Links
    Small windpower a scam ? Survey says SO
    Truth About Skystream & SWWP

    Our host also sells wind--but generally tries (disclaimer: My impression--I have no business relationship with NAWS nor do I speak for them) to get people started with solar PV systems instead. Solar Panels will provide power for decades with little maintenance (good hardware). Wind Turbines--even the best of them--require quite a bit of work (and sometimes money if you need a crane to service) to keep running.

    In general (from what Windsun has posted here before (Neither Niel or I, the moderators, have any connection with NAWS and this forum other than as volunteers to keep the spam to a minimum)--Most of NAWS revenue comes for Solar Electric/PV Panel installations, and most of their complaints/difficulties come from wind turbine installations.

    Wind power goes with the Cube of the wind speed (to the power of 3)... Below 12 mph, there is just not that much power in the wind... Basically, large turbines (large swept area) and tall towers (60'+) away from trees/buildings (300-500 feet +) in a windy location (trees "flag" from prevailing winds) is a minimum for a successful installation.

    We all would be very happy to answer questions to the best of our abilities (I can move this to a new thread for your own discussion)--but if you are into DIY Wind, those two other forums/sites would probably be well worth your time to investigate.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #25
    Re: Solar attic fan - worth it?

    HI,

    I'm shopping for a solar attic fan to replace a powered one that is too noisy. On hot summer days my powered fan runs well into the evening, sometimes till midnight till the attic cools enough for the thermostat to turn it off (I have it set at about 125 degrees f). With a solar powered fan, I'm concerned that the attic will still be pretty hot when the sun goes down at which time the fan will stop running.

    Do solar attic fans typically have, or does anyone know of a model that includes a battery system for use beyond sunset? Or, perhaps, a solor/powered hybrid that runs on solar while the sun shines then switches to powered on cloudy days or after dark?

    Thanks -- Dan
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #26
    Re: Solar attic fan - worth it?

    If you have grid power---You are much better off running the AC powered fan. They will move much more air and (typically) last longer than the DC versions.

    If you add a battery pack--the "power cost" (panel+charge controller+battery) of an "off-grid" battery backed fan will be about 10x will work out to what you current pay for utility power.

    If you want a quieter attic fan--probably look around for a larger unit with a lower sound rating. Also, check that you have enough inlet air and exhaust air square inches for your home... I think that older homes have way too little venting vs what people use today.

    My two cents worth.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #27
    Re: Solar attic fan - worth it?

    Can you wire a Solar DC powered attic fan to work with alternative power source like a AC to DC converter during the night when there's no sun ? Thermostat controlled of course. Let the sun power it and manual overide it with AC on demand.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #28
    Re: Solar attic fan - worth it?

    Recently I worked a convention involving the oil industry, and they developing procedure for recycling roofing shingles. If memory serves, they were estimating that 40-50% of the petroleum content could be recovered from a single shingle, but no one had standardized policy. It was odd that they were considering all the oil locked up in discarded resources.
    dale wrote: »

    Insulation always helps. People rarely consider the effect of shingles. I think all new ones have a reflective quality, but I'm not sure how it is rated. I heard that it increases the life, but don't know if that means 30 yr is more reflective than 15 yr ones.

    I do know that after replacing hot (black) tar roof, the house was noticeably cooler. This might be worth investigating if you re-roof.
    Good luck,
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  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    #29
    Re: Solar attic fan - worth it?
    qprint wrote: »
    Can you wire a Solar DC powered attic fan to work with alternative power source like a AC to DC converter during the night when there's no sun ? Thermostat controlled of course. Let the sun power it and manual overide it with AC on demand.

    I've been looking into this recently.

    All of the Solar powered vent fans I've seen have really pathetic CFM ratings or they are really expensive.

    Given that their CFM ratings are for optimum conditions, this means that most of the time they won't even reach their rated CFM.
    Add in the fact that the roof stays hot long after the sun goes down as the heat slowly soaks through.

    So I figure that solar attic fans are not much good unless you have no other option (slightly better than nothing)

    In my research -when you compared CFM to power consumption- the most efficient, and cheapest fans, were A/C powered attic vent fans (some not all). Most of these already include a temperature sensor.

    Since all my AC now comes from solar, that's the route I'm going.

    This is the one I'm considering, 1650 CFM and only draws 250 watts
    http://www.amazon.com/gp/product/B002TXL5P0/ref=ord_cart_shr?ie=UTF8&m=ATVPDKIKX0DER

    If someone knows a more efficient model with similar CFM please let me know.

    FWIW our house uses a swamp cooler, last year I installed "Up Ducts". This allows you to keep your windows closed and route the ventilated air from the house up through the attic space.
    I'm going to measure my attic temps this year to see whether or not I need to add the attic vent fan. Near as I can figure the vent fan would only run in the early part of the day before the swamp cooler kicks in, but if I can delay the time it takes to heat up the house then I can save both electricity and water.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #30
    Re: Solar attic fan - worth it?

    someone earlier mentioned that they used a car's radiator fan, and that it used a lot of amps. Has anyone measured the current to see how much it is?
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  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    #31
    Re: Solar attic fan - worth it?
    bmet wrote: »
    someone earlier mentioned that they used a car's radiator fan, and that it used a lot of amps. Has anyone measured the current to see how much it is?

    Depends on the fan, I've seen some that draw over 20 amps.
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