Attic exhaust fan opinions needed

[Jimmy9190]

My house is about 1900 square feet, single story 3 bedrooms, 2 baths. The AC works, but is just OK, I have done all I can to be sure it is in good shape, change air filters once a month, clean the condenser coils once each summer, check the drain and check the evap coils for dirt or ice, I go in the attic once each summer and be sure the ducts are all taped up securely with no leaks. Last summer I had to replace the compressor fan motor and run/start caps.

The AC runs pretty much all day from about noon until 7 or 8 at night with the thermostat set on 75. It does cool the house OK but I wonder if adding an exhaust fan in the attic would help improve the cooling efficiency and also lower the electric bills? My electric bill is always around $300.00 each month summer, from about June thru September. I read a lot of mixed info on attic fans online, some say they work well, some say they don't do much.

If I get a fan, I would get the one that mounts to the gable structure inside the attic, not the one that goes thru the roof. House has 2 vents at each gable end, each vent plate is about 16" x 8" from looking at them from the ground. House also has the little soffit vents under all of the eaves arouns the outside perimeter of of the roof. I live near Orlando, Florida. It gets upwards of 95 degrees here in summer and is very humid too. July thru September is pretty uncomfortable outside.

I can get an attic fan for less than $100.00 at Lowe's. I have never had one or installed one before. Do you guys here have any experience with the fans? Do they work or not? Any other info on them?

Thanks for your help on this.

 

[friendly_jacek]

Attic fans are not recommended as they suck conditioned air from home via numerous leaks in ceiling (light fixtures, openings for electric cables, spaces in walls, etc). They can even be health hazard if you have a hot water gas heater inside and negative pressure develops.

My attic is very hot, and while the attic fans (I have 2) lower the attic temp by 10F or so, they INCREASE the electricity use by several kWh per day. I did a 2 month study alternating fans on and off.

Easy to do such a study if you are interested.

If you want to save on cooling, better insulation is the key. I invested in reflective heat barrier. $200 but lots of labor to install it. The attic is now colder than with fans on.

Next time I replace roof, I will remove the fans and add more passive ventilation.

 

[JosephHarmon]

These spinners work very well with vented eves & last year & years. Maybe these things are unheard of in FLA. No more difficult to install than a static vent. They will cool the attic/roof much more quickly.

 

[Jimmy9190]

Thanks. I read that online too, that attic fans can suck cool air out of the living area of the house. I also read a few articles about the reflective insulation you can staple to the rafters in the attic, that seems to me to be a much more viable and effective solution. I just want to keep the house cool and have the AC work the best it can. The insulation in the attic is the old school batts that are laid out in the attic floor. I will do some more research on the reflective insulation, one way or another I want to improve the AC here this year if I can.

 

[friendly_jacek]

I reread your post about $300 per month. I have a bigger home and pay about half of that. Looks like your insulation is inefficient or AC is low on charge. I would check both. It's easy to measure thickness of insulation and AC charge. I don't know about your windows, they could be old and let a lot of heat in. Tinting and shading helps too.

I wish white roofs were available and permissible. My subdivision specifies roofs HAVE to be black. Morons.

 

[Ursae_Majoris]

I would look into attic insulation first. It amazes me that people in the South (where I recently moved) do not know anything about insulation. It keeps both cold AND hot air out of your house and temperate air IN.

Insulate your attic to R-32, insulate around the penetrations in sheetrock on the outside walls and ceiling.
I took my 2 star-rated condo to 5+ stars. Only job I outsourced was replacing 30 year windows with Low-E double pane windows.

Air-leaks and cool-loss is what driving your cost up in summer. You are trying to cool down the neighborhood.

Do you have soffit/eve vents and a ridge vent?
Make sure that soffit vents are unblocked by insulation, install rafter baffles to keep air flow going.
http://www.energystar.gov/index.cfm?c=diy.diy_attic_ventilation

 

[Rodraid]

Originally Posted By: friendly_jacek
Attic fans are not recommended as they suck conditioned air from home via numerous leaks in ceiling (light fixtures, openings for electric cables, spaces in walls, etc).


I did a lot of research last summer and everything I read pretty much said the same thing. My attic floor would reach 140+ degrees during the TX summer. I now have four Whirly Birds and added 12 additional soffit vents, gave me a total of 24 and also put in a foil radiant barrier.

Now my attic only gets 10 degrees above the outside temperature. Those changes were done at the same time so hard to tell which one contributed the most.

I also replaced my heat pump and put in a matching air handler/heat pump. The house is as cool as I want it and uses much less electricity to do it.

Rod

 

[sdowney717]

If you dont have one, put in a ridge vent to passively let the hot ait out. this vent will run all the way along the peak of the roof.

 

[handyman]

I've been installing the foil radiant barrier by myself. It works great but takes a lot of time to do it by myself.

 

[handyman]

Agree!!

Originally Posted By: Rodraid
Originally Posted By: friendly_jacek
Attic fans are not recommended as they suck conditioned air from home via numerous leaks in ceiling (light fixtures, openings for electric cables, spaces in walls, etc).


I did a lot of research last summer and everything I read pretty much said the same thing. My attic floor would reach 140+ degrees during the TX summer. I now have four Whirly Birds and added 12 additional soffit vents, gave me a total of 24 and also put in a foil radiant barrier.

Now my attic only gets 10 degrees above the outside temperature. Those changes were done at the same time so hard to tell which one contributed the most.

I also replaced my heat pump and put in a matching air handler/heat pump. The house is as cool as I want it and uses much less electricity to do it.

Rod

 

[Al]

Ridge vents. I have a power vent on the roof. I really don't run it bc I have the ridge vents. You could go with the spinners or just something like this (no fan). I would go with two of them..both in the center third (lengthwise) so one serves a gable vent on the side.

 

[RTexasF]

I agree with insulation. Years ago we had 18" blown into the attic. The next month (summer) the power bill dropped by $100 and the house was much more comfortable. That winter we never turned the heat on once. Best $800 I've ever spent, made it back that same year in power savings. Where I live you must run the A/C about 10 months of the year, sometimes 12.

 

[Jimmy9190]

Thanks for the info. I agree, fans are not the way to go. I am looking into trying to beef up the insulation and possibly putting in some of the reflective insulation on the rafters. I need to get up in the attic and see exactly what I can do and how to get the job done. The problem is there is not enough room for me to stand up and work in the attic space. No matter what I do this will not be an easy job. I am also going to seal up the windows and doors the best I can, maybe install a shade or blind on the big patio door off of the dining room. Right now it only has a thin curtain and the patio door lets in a lot of heat from the sun through the glass.

 

[JHZR2]

My attic has dormers, so I open one window on one side, put a fan in the opposite window, and let it blow.

 

[Ursae_Majoris]

I could somewhat stand up in my attic. It is dirty, nasty work, and fiberglass works its way in places you did not know you had, but payback is almost immediate. Whatever insulation you put down (blown in or bats), put baffles in by the eves to keep air flowing.
I ended up doing most of the work on my belly on a 12x2 spanning a couple of ceiling beams. Used broom handle to push insulation up against the outside walls. Blow-in type is easier to do, once the baffles are in. Lowes and HD rent the blower to use with their stuff. You will need a helper to feed bags in the machine and to route the hose.

Maybe it is just a GA thing, but I do not see full length ridge vents on houses down here. With proper passive venting, you might not need a fan.

 

[bigmike]

I lived in a house that had little insulation and my A/C ran from around 12PM to 12 midnight, non stop. My electric bill still didn't go over $250.

The house I live in now has vents are off-ridge. Someone who owned the house before me put in a powered fan, but I've never turned it on. When the house gets a new roof, the fan is going to the scrap. No idea why anyone would want to cut a hole in their roof to add a mechanical, powered feature.

Extra insulation and a ridge vent, as mentioned, would be my choices. Easier stuff can be done by yourself as well. Check with a smoke machine (or candle, incense, whatever) for air leaks while the A/C is running.

Better windows, seals, weatherstripping, etc. would all be on my list of suspects. Room darkening curtains or blinds also help.

Most attics really are poor here in the SE. It's difficult to do any kind of work in them. I always wear long sleeves, gloves, tape up my shirt sleeves to my gloves and tape up my jeans to my boots, when going into attics. Not only due to fiberglass making your life miserable, but who knows what else is crawling around with you.

Bad time of the year to be going up in there, but it's better than July or August.

 

[sleddriver]

I've done quite a bit of work on my house over the years to increase comfort & lower the bills. Glad to hear you keep your coils clean. I would also add to check the indoor squirrel cage blower vanes. If you can rake dirt out of them, they need cleaning. Once the curved vanes fill up with gunk, they'll no longer move much air.

You've checked your ducts (supply side) for leaks, what about the return side? I have a vertical unit in a small closet in my house and the return grill area was too small for the blower. In addition, this air box or plenum wasn't sealed so it was sucking dirty air downstream of the filter between the stud walls and from the attic. Sealing it all up meant only conditioned, filtered air was moving through the evap coil.

Stick a small meat thermometer into your supply plenum for a minute or two and note the reading. Then measure the air temp flowing into the return filter. The delta T should be close to 20°. If not, you might be low on refrig.

Does the Sun shine directly on your roof or do you have shade trees? Dark colored shingles? I sprayed a radiant barrier paint onto the underside of my roof decking about 17 yrs ago. It did help. I can easily stand in most of my attic though.

I use a continuous ridge vent with enough eave vents to provide intake. The temp 2' above my attic floor is usually within 10 - 15° of outdoor ambient.

It's important to seal up as many ceiling penetrations (plumbing stacks, electrical wiring through the top plate, light cans, bath/kitchen vent ducts,etc) as possible in addition to open fur downs & cavities. Also seal the gaps under your sinks where the plumbing comes through the wall.

In your area the AC has a high latent heat load due to the humidity so you need a cold evap coil to sweat the water out.

I used to use the powered attic vent fans before the ridge vent. The problem is the motors are cheap. They'd run for a few years then seize because the bushings dried up. The plastic tops would also crack, then you have a hole in your roof for the rain to enter. Not good. I ripped them out after cutting in the ridge vent.

Finally, last summer during the big heat wave here in Tx. I started hosing down the roof after the sun set. Since water has a high specific heat, it absorbs a lot of heat upon evaporation. It would quickly drop the attic temp by more than 10° after 40 min. Direct the water at the ridge and let it flow all the way down to the eaves from one side to the other. Then stop.

May not be as effective as where you are because your humidity is much higher than here.

If you want to read up more about cooling loads, get a copy of Manual J from ACCA. If your local library doesn't have it, ask them to borrow it from another library. I crunched all the numbers to calculate the per room loads for my house before designing & installing a new duct system. Made a HUGE difference as my old duct system was too restrictive on both supply & return sides.

 

[sleddriver]

Originally Posted By: Jimmy9190
Thanks for the info. I agree, fans are not the way to go. I am looking into trying to beef up the insulation and possibly putting in some of the reflective insulation on the rafters. I need to get up in the attic and see exactly what I can do and how to get the job done. The problem is there is not enough room for me to stand up and work in the attic space. No matter what I do this will not be an easy job.

I use a XXL or larger Tyvek bunny-suit, a cotton painters cap on my head and a respirator when up in the attic. The Tyvek suits you can get at a painters store, WW Grainger, on-line, etc. Works great for keeping all that stuff off your clothes.

You may have to lay down ply in order to move around up there. When I sprayed the radiant barrier in, I bought a 18" extension wand so I could reach further down to the eave without having to crawl.
Quote:
I am also going to seal up the windows and doors the best I can, maybe install a shade or blind on the big patio door off of the dining room. Right now it only has a thin curtain and the patio door lets in a lot of heat from the sun through the glass.

Bingo! Very important to keep any solar radiation off of your windows, doors and especially sliding glass doors. Shade them from outside with a solar screen to keep radiation off of the glass, metal frames, etc. They can really heat up when exposed to the Sun for hours on end.

Good luck.

 

[Cujet]

One of the best things you can do is to go with a bright, white roof.

I custom built my current 2500sq/ft under air, home (S. FL) and it was designed with energy efficiency in mind.

My previous home was 1200ft home was actually more expensive to cool in summertime.

It's difficult to quantify the radiant heat that a conventional roof produces. In mid summer, stand mid room and see if you can feel warmth from above. It's quite possible that radiant heat is increasing the work load on your AC by a significant amount. No amount or type of insulation will help this. Short of a radiant heat barrier. Or, as I mentioned, a bright, white roof.

My current house has a brilliant white barrel tile roof. The attic has 2 solar fans at the peak. The eve's are well vented. My attic is never hot, even mid July! I can work up there without issue. In fact, I have a bonus room over the garage and it remains cooler than the peak temp outside, always.

My builder was baffled by the fact that I did not want "super" insulation above the ceiling. I told him that heat rises, and I'm not trying to trap any heat. He laughed quite hard. But, the truth remains, attic insulation won't help radiant heat issues. If your attic is hot, your AC will work harder.

 

[JHZR2]

So it seems that nobody really has a walk up attic? Ive always loved and lived in older homes. All this discussion of crawling around and tyvek suits in the attic, what kind of worthless space is that???!?

I walk up in my underwear if I want, stand upright, and use it for storage. Its neither that hot or cold.

If one insulates too much up against the roof, does not it damage the roof?