Replies

1. 
   Guest_ | Feb 06, 2000 08:37am | #1

   *
   RTFA

1. 
   Guest_ | Feb 06, 2000 09:43am | #2

   *...Mike.....are you sure about the 650 CFM ?........I sell Fan Attic by SunTunnel....and if you are thinking of a "whole house fan" the solar powered ones make a lot of sense......don't mind FredL...he likes to make blanket statements about things he doesn't bother to find out the circumstances of..(wow, that was a clumsey phrase ...)...but that's OK.. he keeps me amused...I think he means he'd like to have some more information about your particular situation so he can make an informed recommendation as to YOUR options........b but hey, what do I know... I'm just a frog...... Kermit

1. 
   Guest_ | Feb 06, 2000 07:25pm | #3

   *Dear Fred:You add a lot to this forum. You have gotten me to think about "weatherization" items in ways that I had not looked at them before. You have heightened my awareness to the importance of making the building envelope airtight and the doubly detrimental effect of air leaks based of the fact that air movement carries moisture with it. You have shared techniques for accomplishing these things. Thanks for all of that. I also find your writings and writing style amusing at times.Obviously, in your above post you are trying to get this guy to think about things in a different light. Only problem is that sometimes your heavy handed approach, your above posting, case in point, breeds contempt and inflammation.Respectively,Matt

1. 
   Guest_ | Feb 06, 2000 09:43pm | #4

   *Mike,

   I'm wondering if this is an issue of operating cost of the fan? If its solar powered it doesn't cost anything to run. Maybe. There are problems with mechanical ventilation that one would first need to understand before you can make a decision on whether to use it.

   If your concern is lowering the attic temperature in the summer, you my want to read the article by TenWolde & Rose. I personally haven't draw a conclusion to the validity of their findings. But, the article is informative none the less.

   As the guru points out you will be drawing in hot moist air into your attic when you use the fan (in the summer). But, most likely if your attic is already vented there's hot moist air in it to being with.

   Other problems associated with this type of venting/fan is control. How would you control it? A switch, thermostat, or humiditstat? The controls for this device can become quite complicated.

   The major problem of these devices is that they create a negative pressure in the attic. This means that they will draw air not only from the provided vents (soffit) but, from any opening in the attic ceiling/floor barrier. If this should occur you will in effect draw cool conditioned air from the living space into the attic creating a condensation problem. If you chose to use this type of vent it is of even greater importance that you air-seal your attic ceiling/floor.

   If you don't use air-conditioning there's not a reason to worry. My own personal opinion is not to use a mechanical vent.

   Joseph FuscoView Image"Whenever, therefore, people are deceived and form opinions wide of the truth, it is clear that the error has slid into their minds through the medium of certain resemblance's to that truth." Socrates

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   Guest_ | Feb 06, 2000 10:19pm | #5

   *The question I would have is whether having a single or primary venting spot in the attic might create "dead spots" that don't get adequate ventilation. Then, when the roof surface cools down at night, those areas might see increased condensation.As suggeted above in the thread, be sure to balance the input with the output. If the solar powered vent is pushing a lot of air out of the attic, the makeup air has to come from somewhere. If it doesn't come in thru soffit vents, it'll get sucked from the living spaces, which in turn will suck air from the outdoors (or maybe even create backdrafting thru your water heater flue.)Come to think of it, a possible problem with power vents would be balancing the inlets/soffit vents with the variable output of the power vent. I don't know if there would be a problem with too much soffit inlets when the power vent isn't runnng. Hard to see how it could be a problem, but sometimes this stuff isn't obvious.As a home inspector in NW Ohio, I see a lot of attics. I find it hard to deduce many clear rules about attic ventilation, there are so many variables.Some trends I've seen: houses on very wet crawls are at highest risk for major condensation and mold (even sometimes, decay) on the underside of the roof surfaces.The north plane of a roof is more likely to have condenstion and mold.Roofs with continuous ridge and soffit vents are least likely to have evidence of condensation.Bath fans should be vented outdoors, or, at least terminated next to a thru roof vent.Low sloped roofs are possibly more likely to have condensation (usually near the eaves) than higher pitched roofs - although this _might_ be affected by the possibility that lower pitched roofs are less likely to have soffit vents or have those vents blocked by insulation.Bob

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   Guest_ | Feb 07, 2000 09:18am | #6

   *Joe,Thanks for article that is just that kind of in depth info I was looking for. Upon scanning it, I noted that supplemental venting in warm/humid climate is not suggested as a good idea.Mike R B

3. 
   Guest_ | Feb 07, 2000 09:29am | #7

   *Fred,I was not defending the solar powered attic vent fan but wanting opinions on how effective they might be. The show that featured it claimed it significantly reduced the attic temperature, and would therefore make cooling the home air-conditioned space (below the attic) less costly. At first, that seemed believable. The few times I've been up in my attic in the summer here (SE U.S.) it feels like 150 F! But, I have no idea of the climate in which the show demo that featured the solar attic vent was done in. I am learning from several comments that there is a lot of skepticism about the use of supplemental attic venting, especially in warm humid summer climate like I live in.As for more details... 1.5 story 2500 sq. ft. home built in 1990... vinyl siding... No tyvec home wrap (big mistake!?)... a lot (about 2 ft.) of loose cellulose insulation in attic... R13? wall insulation (kind with vapor barrier attached to insulation) on walls with 2x4 studs... continuous soffit vents, ridge vents at peak of roof.The bottom line... wanting to make my home more energy efficient, i.e., decrease AC/heat costs.I'm learning, and that is what I needed! If I understand the point you and others made... supplemental venting in attic (e.g., a solar powered vent) might pull conditioned air from the home into the attic, which obviously would be the exact opposite to what I was trying to achieve. Mike R B

4. 
   Guest_ | Feb 08, 2000 01:39am | #8

   *Mike R B. There has been a lot of testing of real attics on real houses of the effects of power vents reducing attic temperatures.(see my writings on this in the archives).Even if the power fans reduce the attic temperature by 20,0r 30 degrees it has little or no effect on lowering the house's air conditioning bill. But it does have a large effect on your electric bill. The obviuous advantage of the solar powered version is no increase in electric bill. Otherwise it is no more effective than power venting. The most effective and least costly way to reduce heat movement from attic to spaces below the attic is with plenty of cellulose insulation. Remember that the main heat transfer mechanism in an attic is radiation. Radiant heat cannot be flushed out of an attic. GeneL.

5. 
   Guest_ | Feb 08, 2000 05:13am | #9

   *"Vented roof framing is exactly how you would build with the intent of killing the occupants and destroying the house"Rhetoric like that hardly needs a comment.John

6. 
   Guest_ | Feb 08, 2000 09:29am | #10

   *Dear Fred,Okay, I get your point about not wanting to have negative pressure in the attic from a supplemental vent fan, since it might draw conditioned air from the home into the attic...But, on another point you made, I am confused... What is "unblocked framing?" Also, if I understand what you are suggesting, then every home that is built in this region which has continuos soffit vents and a ridge vent is wrong and a danger to occupants!?... Believe me, nearly every new home in my region has exactly that kind of venting. Are you suggesting it is better to have a tightly sealed attic space, with absolutely no ventilation? Remember, my region of country has long, extremely warm/humid summers and mild winters. We certainly don't have to deal with many of the problems in colder climates (i.e., ice buildup on roof).By the way, I just got a back-issue of FHB, Nov. 96, no. 105, and I'm going to read what I believe it is your article "Fixing a cold, drafty house."Sincerely,Mike R B

7. 
   Guest_ | Feb 08, 2000 11:42am | #11

   *Gene, you're right that radiant heat can't be flushed out of an attic, but its because it really doesn't exist like hot air exists. It has no mass, therefore no thermal mass. Its just energy. So it can be repelled. Besides insulation, the only way I know of repelling radiant heat is with a radiant barrier. Tinfoil works. A blazing white roof works. (A sprinkler on the roof is effective too, but its not a radiant barrier) Does anyone have experience with the radiant barriers available to builders? Its craft paper faced with tinfoil, basically.And regarding previous questions about the solar powered fan itself: Yes, its 650 CFM, in full sun with a 14 watt, nomial 12volt panel. Almost twice that (1200CFM) with two panels in series on the same fan. I think its a 48V DC motor. (I used to design and sell solar electric systems, that's whay I know this)There are no controls, Joe. Just the sun. (works elegantly in most cases)A thermostat, or any control for that matter, can be added.As to the cost of running an electric fan, well, it depends on the fan. This one moves 650CFM on 14 watts. (Most AC fans aren't near that efficient.) If it ran 8 hours a day for 365 days a year, and you are paying 12 cents/KWH, then it costs $4.90 to run. Per year. The fan and panel combo is close to 200 bucks, I believe. Then again, you might pay the electrician more than that to run power to the fan.

8. 
   Guest_ | Feb 08, 2000 04:14pm | #12

   * Thomas,

   I just would wonder how the fan would work, lets say at night? Where it can be sometimes hotter then the day.

   Joseph Fusco View Image "The price of apathy towards public affairs is to be ruled by evil men." -- Plato

9. 
   Guest_ | Feb 08, 2000 09:07pm | #13

   *Thomas - as far as I can tell from my own experiences cellulose is an effective and long lasting radiant barrier.

10. 
    Guest_ | Feb 08, 2000 10:29pm | #14

    *$200 would add a nice layer of cellulose to your attic helping heating and cooling bills. I feel that some ventalation is needed in an attic because the ceiling is never perfectly sealed. A small amount of venting will allow the small amount of moisture to escape that leaks thru the imperfections in the ceiling even if very well built (or thru roof leaks). How small of vents? I don't know but it seems to be a lot less than even the code minimum in areas that require venting.In my house, I installed the ceiling dry wall before putting up the interior partitions. All holes around pipes wires etc. were sealed with foam and the attic was insulated with cellulose. The ridge has a filter covered mesh shingle-over Cobra vent and the soffits have a 1.5" wide perforated aluminum strip. This 1800 sq.ft. house uses a ONE ton A/C unit and it is really too large. I am in Long Island NY. The attic is hot in the summer but the house is cool and comfortable. From runtime on the hottest days, I need a 8500btu air conditioner. No one makes a central unit that small.Ron

11. 
    Guest_ | Feb 09, 2000 12:43am | #15

    *Joe,It will work in many climates elegantly. If it needs to work at night, hook the panel up to a 12V battery and run the fan off the battery. There's some efficiency loss; about 20%. Of course now you have to pay for a battery too, and possibly a larger panel depending on your needs. As to whether forced attic venting is better for the house or not, well, I'll leave that up to those with more years under their belt than I.Being one who has always lived the west coast, the concept of night being warmer than day is a strange one to me. Tom

12. 
    Guest_ | Feb 09, 2000 01:04am | #16

    *Bill, Right, cellulose works. But if the object is to keep heat out of the attic, where are you going to put it? Its usually blown in and over the cieling joists, right? Now, I know there are ways to insulate the rafters, but would that cause yet another condensation problem between the insulation and sheathing? What if there was a small, well ventilated air conduit between the insulation (or radiant barrier) and the sheathing? Will that solve the condensation problem? Will the attic be cool(er)? You builders can go ahead and snicker if I'm describing some standard practice that I'm not aware of. Educate me!Listening,TomP.S. Oh yeah, that's what those plastic corrugated sheets are for, huh? To define an air space for venting? I think I'd rather use foil faced rigid insulation with wooden battens to define the vent space. Thoughts?

13. 
    Guest_ | Feb 09, 2000 05:02am | #17

    *Don't bother replying to my questions. I found answers in the "consensus" thread above. Its still welcome if you gotta say something, though!Tom

14. 
    Guest_ | Feb 11, 2000 03:41pm | #18

    *Fred,I'm not an expert or anything, but it seems to me that an attic (other than a finished attic) is differnt than the living spaces. So, perhaps, we might do things differently.FWIW, in the CO testing I do, I haven't seen trend towards lower draft on the combustion appliances where an attic is well vented as opposed to minimally vented, although I probably haven't done enough to draw any firm conclusions.Interesting sidelight: The Ohio EPA is now recommending installing CO alarms in basements when a radon mitigation vent is added. Their concern seems to be creation of negative pressure in the basement and possible backdrafting. Any comments?Bob

15. 
    Guest_ | Feb 11, 2000 06:09pm | #19

    *.....Bob et al....I'm beginning to think that there is much less controversy over this than i frist imagined...vapor barrier/ soffit vent/ ridge vent: McCoysvs.air retarder/ densepak / no vent : Hatfieldsboth advocate (STRONGLY) seperating the comfort envelope from the attic space, both take great pains to ensure there is no short circuit or direct paths for conditioned air to be sucked or pushed into the attic...a lot of it is counting the angels dancing on the head of a pin...as far as the solar powered attic fan... all the research from the mfr. and their lab testing tells me that this is a great replacement for a utility grid connected attic fan...the controls are foolproof...if the sun is out it turns on....it will exhaust 650 - 800 cfm.. and if all the gaps are plugged to the comfort space, it will be pulling in relatively cooler air (say 90 deg) and oushing out say 120 deg.not my cup of tea... but another great retrofit tool for our kit bag...so short of reroofing and changing the shoingles from black to white... I think this is a great device

16. 
    Guest_ | Feb 12, 2000 07:15am | #20

    *Fred,I was just pointing out that when I do a CO analysis (following the BPI protocol) I check drafting during the testing. I haven't seen any correlation between types of roof venting and the draft readings I get. (I suspect there are too many variables: age of house, tightness, weather conditions, etc.)<> Not where I am (NW Ohio.) I rarely get more than 001-002 ppm diferential between outdoor ambient and indoor. When I have, there's been a distinct cause: ventless "heaters/logs" and, in one case, an attic furnace installation that the installer should be made to sleep next to. Just for one night. That oughta do it.OTOH, any case with 10ppm or more should be immediately dealt with, IMO (or > outdoor ambient if infants or the infirm are present). The health effects of chronic exposure to low level CO can be devasting, and more people ought to be aware of that danger.Bob

17. 
    Guest_ | Feb 13, 2000 08:21am | #21

    *Dear Fred,Upon rereading your response (... "there is no doubt that an attic with no intentional venting and tightly sealed (I guess, part of my difficulty with the idea of a tightly sealed attic is that it is so common here in S.E.U.S. to passively vent the attic via soffit to ridge vent air movement, and I am having a hard time, if what you describe is correct, to accept that so many builders are wrong on this method.I thank you and all the others that have provided the many responses and threads. This was my first attempt at a discussion like this, and it sure has been helpful.Sincerely,Mike R B

18. 
    Guest_ | Feb 13, 2000 08:53am | #22

    *.hey Bob Walker... I'd like to know if you've seen much of the air-to -air heat exchangers in your inspections ...and your first impressions and then your conclusions... I've been inadvertantly doing air-to -air in some of my houses (solar hot air collectors)... now I want to start actually DESIGNING for the fresh air make up and develop a strategy for combustion air.....and anyone else, don't be offended if I addressed that to Bob.....I'm going to bring this topic up (fresh air makeup ) right after we discuss wall construction in the VENT/NO VENT thread....Mike Smith

19. 
    Guest_ | Feb 13, 2000 05:18pm | #23

    *Mike,Sorry, haven't seen _any_. They must be illegal or something in NW Ohio Bob