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Message |
    
SOSully
Citizen
Username: Sullymw
Post Number: 1209
Registered: 5-2001
| | Posted on Monday, April 3, 2006 - 2:00 pm: | 
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I am having my roof replaced soon and the roofer suggested installing a powered ventilator fan to cool the attic. I don't currently have soffit vents or gable vents. I've been doing some research on the Internet and there are lots of conflicting opinions. Some people say never use powered ventilation because it sucks cool air out of your living space. I don't know if that is true or not. Also, those fans work with a thermostat and thus give no ventilation in the winter. Another suggestion I have seen is for an unpowered turbine ventilator which can draw large quantities of warm air out of the attic and it also works in the winter to remove moist air that can lead to condensation. I don't know how well those work. Opinions one way or the other? |
Two Senses
Citizen
Username: Twosense
Post Number: 427
Registered: 7-2004
| | Posted on Monday, April 3, 2006 - 5:53 pm: |
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Make sure you follow the manufacturer's recommendation for adequate soffit and/or gable vents surface area, or you'll pull interior air from your living space, including deadly carbon monoxide from your heating system. |
Jgberkeley
Citizen
Username: Jgberkeley
Post Number: 4520
Registered: 5-2001
| | Posted on Monday, April 3, 2006 - 8:44 pm: |
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Have the roofer put in a small power vent, and make sure that the roofer installs a gable or soffet intake for it.
And, have the roofer install passive ridge vents as well.
You can over think this, however you will never regret doing as I suggest.
Later,
George |
Eponymous
Citizen
Username: Eponymous
Post Number: 167
Registered: 6-2004
| | Posted on Wednesday, April 5, 2006 - 1:52 am: |
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SOSully,
Ventilate it.
You get no _added_ ventilation in winter, but you'll get unaided ventilation just from having an attic that has vents in it. Generally speaking an unused attic doesn't need to be cooled in winter.  |
Jgberkeley
Citizen
Username: Jgberkeley
Post Number: 4524
Registered: 5-2001
| | Posted on Wednesday, April 5, 2006 - 8:28 am: |
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All attics need to be vented in the winter to allow the moisture that passes through your house to get out, and avoid the rot.
Vent. Combo of active power vent for the summer and passive ridge vents for the winter.
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tourne
Citizen
Username: Tourne
Post Number: 460
Registered: 1-2003
| | Posted on Wednesday, April 5, 2006 - 10:23 am: |
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Search for Solar Attic Fan, see www.efi.org or other sites, solar powered attic vent fans work great, need no wiring, are easy to install, and will not increase your electric bill. They work all year long. |
tourne
Citizen
Username: Tourne
Post Number: 461
Registered: 1-2003
| | Posted on Wednesday, April 5, 2006 - 10:33 am: |
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Sorry, EFI consumer site does not sell fans. See www.solatube.com/res_solarstar.php, instead. |
Travis
Citizen
Username: Travis
Post Number: 385
Registered: 6-2004
| | Posted on Friday, April 7, 2006 - 5:06 pm: |
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Venting of attics (ridge and soffit vents) comes out of research done in homes in Minnesota in the 1930s. It is open to debate if that research is applicable to houses in NJ. It does remove moisture in the winter, but it also removes heat (your energy bills). Are winters in NJ long and severe enough that moisture accumulation is an issue? In the summer, it allows warm moist air into the attic. If you've got CAC with an air handler in the attic, you've now got (a) condensation problems when the moist air hits cool air leaking from the air handler and (b) cooled air venting outside (more lost energy).
I've found that ridge and soffit vents do a good job of cooling the attic in fall and spring, during cool nights. I haven't noticed that it does much to keep the attic cooler in summer months. It surely makes it colder in winter, and brings in a lot of dust.
It is a bad idea to combine ridge/soffit vents with say gable vents. The air current from the soffit vents gets redirected to the gable vent and defeats the purpose of the ridge/soffit vents (to direct an air flow over the roof deck).
Houses aren't easy. |
Eponymous
Citizen
Username: Eponymous
Post Number: 173
Registered: 6-2004
| | Posted on Friday, April 7, 2006 - 5:40 pm: |
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Travis,
Venting of attics is standard practice and, as I well know from my own experience, significantly reduces the heat build-up in the attic during the warmer months.
The vast majority of that heat comes from the sun, not the interior of the house, so in the winter, the attic doesn't heat up much because there's less sun at a lower angle. So the temperature difference between an unvented and vented attic is much much less then. That is, heat transfer between the house and attic is the same during winter whether the attic is ventilated or not.
This transfer of heat between house and attic is a separate issue. Attics should be vented and their floors insulated. That will prevent heat transfer between the house and the attic all year 'round. Again, when I insulated my attic floor, I could tell the difference on the upper floor of the house. It was noticeably warmer in the winter.
(I'm not up on CAC, but perhaps you shouldn't have your air handler in the attic then. Isn't the handler always outside of the cooled space? How does losing the leaking cool air in the attic differ from losing it somewhere else? Also a vented attic is only a bit warmer than the outside air, and shouldn't carry much more moisture, so you shouldn't see much if any more condensation in the attic then, say, out back.) |
Jgberkeley
Citizen
Username: Jgberkeley
Post Number: 4532
Registered: 5-2001
| | Posted on Friday, April 7, 2006 - 9:12 pm: |
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Hey, do not forget that the vent of the attic in the winter is to remove moisture venting from the house. It is not all about heat.
On A/C systems, the compressor is always outside and designed to vent the collected heat into the air.
The air handlers are often in the attic, basements or other void spaces. If properly installed and maintained they do not leak cool air and are insulated to avoid BTU loss in any heat around them. Correctly installed air handlers will have summer moisture from your house condense on the 'A' coils and on some entry pipes and joints, very normal. All have systems to trap and drain away the water that condenses out of the warm moist air. |
Travis
Citizen
Username: Travis
Post Number: 386
Registered: 6-2004
| | Posted on Saturday, April 8, 2006 - 7:44 am: |
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When I said venting removed heat during winter, I was referring to your energy dollars going out the ridge vent.
Air handlers are not sealed against leaks, and their insulation is a joke. No-one would pay the price that would be required for a properly insulated air handler.
Quote:Venting of attics is standard practice
Why is it standard practice? Where are the studies? Where's the data?
There are plenty of other standard practices that are recognized as big mistakes. Venting of crawl spaces. Plastic vapor barriers. Gable vents in addition to ridge/soffit vents. Houses are complicated systems, and many practices and code requirements come out of an era when energy conservation was not even on the horizon. Some of these practices were also developed for completely different climates than NJ (and NJ's climate itself is changing with global warming).
My favorite anecdote from a building scientist: when he got into construction in the 70s, he built an energy-efficient house "by the book."
It had to be demolished because of mold problems.
He stopped blindly accepting "standard practice" and started investigating why things were done in certain ways.
I'm not even arguing against venting attics, just pointing out the pitfalls. If you don't vent, there are plenty of things you need to do to avoid moisture build-up, especially in these old houses with no VB in the basement floor. For many, it seems to be easier just to do things the way they've always been done. Hence you've got no air sealing of the envelope, POS insulation like FG, etc. |
mbb
Citizen
Username: Mbb
Post Number: 5
Registered: 4-2006
| | Posted on Saturday, April 8, 2006 - 9:16 am: |
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I found that attic ventilation is important in this area because a warm and moist attic provides excellent breeding ground for little flies and moths. If you are exhausting bathrooms into the attic, attic ventilation is a must.
An attic/roof fan should work with some type of vent in the attic. This will allow incoming air to sweep away the moist warm air generated in the house. Without a vent, the fan will suck air out of the house. In addition to higher heating and AC bills, the negative pressure created by the fan may cause radon to be brought into the house from the ground under the foundation. Somebody mentioned earlier CO problems, too. You can bypass the thermostat by installing a power switch to turn the fan on/off whenever you want to do so. Finally, before you add vents (with/out powered fan), make sure there is good insulation between the attic and the top floor. Any recessed lights on the top floor ceiling must be insulated and covered. Otherwise you'll get a cold draft coming down from the light rims in the winter.
I am just a home owner. Live and learn...
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Travis
Citizen
Username: Travis
Post Number: 387
Registered: 6-2004
| | Posted on Saturday, April 8, 2006 - 12:41 pm: |
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Quote:attic ventilation is important in this area because a warm and moist attic provides excellent breeding ground for little flies and moths
That doesn't make sense to me. Vents allow warm moist air, insects and other critters into the house.
A bathroom fan should never ventilate into the attic. Never.
A couple of times now people have mentioned negative pressure and drawing carbon monoxide from the exhaust flue. It is perfectly okay to exhaust house air in spring and fall. Tamarack sells an efficient house fan that sits on the attic floor and exhausts house air into the attic, to then be exhausted via the ridge vent. The fan has motorized doors that close up when not in use, for winter. This is a low-cost alternative to AC, which is not required in this climate until summer. Just make sure you've opened some windows before you turn it on.
With all due respect, I think people have the wrong end of the stick with respect to where and why they should ventilate. In the summer, it's questionable how much benefit you'll get from drawing warm muggy air into the attic. The whole argument for ventilating attics is based on removing moisture from the roof deck in winter, before you get condensation and rot. I know some houses have gable vents and fans to exhaust the attic in summer, but that gable vent short-circuits the soffit-and-ridge vents.
It is commonly recognized that, as mbb says, you should seal the building envelope from the attic to prevent air leaks, as part of proper insulation. But if you do this, (a) haven't you reduced the need for attic ventilation and (b) you now need to ventilate the building envelope. This may not be necessary in winter, the boiler is going to be creating negative pressure and drawing in outside air, but it may still be necessary in spring and fall. A good way to achieve this ventilation is simply a bathroom fan (say a quiet Panasonic fan) on a timer switch, or even just left to run. With this, you now have some control over the amount of air leakage, unlike the "leaky house" approach which just lets your energy dollars leak out of the house. Even better, if you have AC, is to add a small duct to outside to the return, to control where the intake air comes from (not say via the crawlspace), and use the air handler for ventilation. But the running costs are higher than the bathroom fan approach. |
mbb
Citizen
Username: Mbb
Post Number: 6
Registered: 4-2006
| | Posted on Saturday, April 8, 2006 - 1:28 pm: |
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From previous e-mail ... "Vents allow warm moist air, insects and other critters into the house" ...
A mesh over the vent opening keeps "critters" out. |
george H
Citizen
Username: Georgieboy
Post Number: 152
Registered: 8-2005
| | Posted on Saturday, April 8, 2006 - 5:25 pm: |
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I always thought that the main purpose of soffett/ridge vent,at least in our region,was to keep the underside of the roof sheathing,close to the outside temp.,to avoid snow melt and re-freezing on the unheated portion of the eave,thus causing the dreaded ice dams.This of course only applys in the winter.As far as summer goes,following the concept of hot air rising,I would think that air escaping out the ridge vent is being pushed by air entering the soffett vent thus creating a loop of sorts where air is constantly moving. |
SOSully
Citizen
Username: Sullymw
Post Number: 1226
Registered: 5-2001
| | Posted on Saturday, April 8, 2006 - 5:39 pm: |
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We also have a broken gable attic fan with louvers but it is broken. It's probably a good idea to replace that fan rather than add another one. The only problem is that there is no corresponding gable vent on the other side of the house. How do you figure out how to size the gable vent? |
Travis
Citizen
Username: Travis
Post Number: 388
Registered: 6-2004
| | Posted on Saturday, April 8, 2006 - 5:44 pm: |
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George, yes, preventing ice dams is another motivation for attic venting. The alternative is to insulate the roof deck, typically with spray foam. The trick is, you've got to get this just right or you'll get warm spots on the roof deck that will lead to ice dams.
Ridge-and-soffit vents may give you a running air current over the roof deck in summer....but to what purpose? Condensation and ice damming in winter are the problems. |
Jgberkeley
Citizen
Username: Jgberkeley
Post Number: 4533
Registered: 5-2001
| | Posted on Saturday, April 8, 2006 - 5:51 pm: |
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Ridge vents with soffit intake vents allow hot air to rise out of the attic and cooler, air to enter in thru the soffit, allowing the attic to keep the temp of the roof deck more stable than if you had nothing. Power venting will increase the effect and help your roof to live a longer life. |
Travis
Citizen
Username: Travis
Post Number: 389
Registered: 6-2004
| | Posted on Saturday, April 8, 2006 - 10:09 pm: |
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I'm really trying to stay away from this, but I have to add this:
It's been said several times in this thread that ridge-and-soffit vents will cool the roof deck in summer time.
There was a study done in Las Vegas of vented vs unvented attics. The observed difference in roof deck temperatures in the approaches was 17*F. Not significant.
Again, I'm really not advocating for hot roofs. I can make arguments against unvented attics as easily as against vented attics. For example, an unvented (and therefore insulated) attic must be heated in winter time to avoid condensation, that means not insulating the floor of the attic. Do the energy savings from reduced AC load warrant the increased heating load? There's some research on this for hot-humid climates but not much for NJ's current climate, so all we're left with is a WAG. Many factors can come into play. Many of the houses around here have 2x6 joists in the attic, so it'll be hard to properly insulate the attic floor. With cells the best you'll do is about R-20; code now requires R-50. I know in NE some people will stack an extra layer of joists perpendicular to the existing joists to double the space for insulation. Whether you have a walk-up attic will also be an important factor.
Like I said in my original post, houses aren't easy. |
Eponymous
Citizen
Username: Eponymous
Post Number: 174
Registered: 6-2004
| | Posted on Sunday, April 9, 2006 - 12:58 am: |
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an unvented (and therefore insulated) attic
I'm up too late, but you need to define this. Venting and insulating are two different things, as I understand them.
Roof deck means the surface of the roof, right? Not the floor of the attic. The concern in the paper was for the material out of which the roofs were made.
And where's the condensation forming that you're talking about?
As for the study you cite:
1. It was for a "cooling climate" or "hot-humid climate". I don't think NJ qualifies, to say the least. The big problem they're concerned with is humidity in the attic in these high-humidity areas. In Las Vegas, as they say in the paper, the typical minimum winter temp is 45.
2. The houses in one simulation had:
1:150 vented attic, R-28 ceiling insulation, ducts in attic, no duct leakage, R-5 duct insulation,
R-19 walls, double glazing, black roof shingles
3. Compared to the number of variables they discuss (e.g., roof-tile color, ductwork, leakage, venting), they ran very few test cases (i.e., 2). |
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