Was wondering whether installing a thermostatically-controlled attic fan would pay for itself in Minnesota. Our second story is hard to cool down even with central-air in the summer time.
With an attic fan would I have trouble with the blown-in insulation in my attic being blown around?
Appreciate any comments.
Replies
Cannot say enough good things about my Tamarack Tech whole house fan.
Cools the attic and the house.
Quiet, seals tight, easy install, low energy consumption...
You would need to build a 'dam' to hold back the insulation, but it does not blow hard enough to cause troubles.
Just something to consider as a alternative to a typical roof or gable fan...
http://www.tamtech.com/hv1000.htm
I have three, each wired for a different temperature and a manual overide that can turn it off or on manually. I love mine, but carefull wiring will make it a nice product.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Bob, do you have duct work in the attic?
What type of ventilation up there, ie., soffit vents, gable vents, ridge vent or roof vents?
What is your attic insulation and depth?
Do you have an idea of summer attic air temps?
Is the upstairs staying hot long after the sun goes down? Roof black?
Do you know the A/C tonnage serving the upstairs and the sq footage?
It will be easier to advise with this info.
Paul
Paul, this is in response to your reply to my letter asking about the feasibility of putting a thermostatically-controlled fan in my Minnesota attic:
I have a 16 year old 2500 sq. ft. two story house with natural gas forced-air heating system with a 1 1/2 ton central A/C unit. The upstairs is probably 600-750 sq. ft. There is no duct work in the attic. There is roughly 12" of blown cellulose insulation in the attic which has soffit vents as well as roof vents. The roof has one year old black shingles and I have no idea how hot it gets in the attic in the summer, but the upstairs stays warm long after the sun goes down.
Thanks in advance for your help.
Bob
I suspect that you will do a lot better looking at where vents, speically the return air, are located and the balancing of the vents.
Bob, Let me ask a few more questions.
Are you saying you have only 1 1/2 tons of A/C for the whole house (2500 sq ft), or for only the upstairs (600-750 sq ft)?
Where is the air handler located that serves the upstairs?
Do you have metal ductwork in the walls, or is the hollow wall the actual duct?
Where are the upstairs supply vents located...floor, low on wall, high on wall?
How does the air velocity feel coming from the upstairs vents compared to the downstairs vents?
Do you have dampers on the ducts coming off the main trunk lines for each room or zone?
How many return air grilles do you have and where are they?
Do you have a gable roof or hip roof?
Where were you thinking of mounting the attic fan?
Is the downstairs "cool" in the winter, ie., difficult to heat compared to the upstairs?
Sorry for all the questions, but the more I know about your situation, the better advice I can offer. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Paul, The A/C is actually 3 tons, my mistake. The metal ductwork is in the walls, with supply vents located on the floor by the outside walls. There are return vents in all three bedrooms and in the hall, all located high on an interior wall. The air velocity feels good upstairs except for one bedroom that has poor air flow. It's always the coldest room in the house. The upstairs as a rule is more difficult to heat in the winter compared with the main level. I had a squirrel cage duct booster on the ductwork for that room where it came off the furnace in the basement but it was noisy and didn't help much. I remember seeing dampers on the ductwork, they were all open, but now the basement ceiling is finished and they are for the most part inaccesible.
I was thinking of mounting the fan in the gable end of my gable roof, or as a roof mount.
Thanks.
Bob, thanks for the extra info. Here is what I gather and suggest.
You have 833 sq ft per ton of A/C capacity. That is a stretch for most houses on hot days, unless very tight and well insulated. By tight, I mean both the house envelope and the forced air system.
You are pushing the air from a basement to the 2nd story. Cold air is heavier than hot, and you have a long up hill distance. It would be helpful to be able to partially close some of the dampers feeding the downstairs during the summer so that more cold air was pushed to the upstairs. Understand you can't get to them.
You have about R-42 in the attic, not bad, another R-8 wouldn't hurt, but let's do some other things first.
So what can be done...
Let's reduce the heat load, increase the air flow , and check the A/C performance.
The heat load. I would put in the gable fan, but don't go overboard on cfm. Size it to the sq ft of the attic, and be sure you have adequate outdoor supply air to the attic. The box or paper work that comes with the fan will give you the info. Check that the fan has a high temp cut off in case of fire. You can use either a timer or a thermostat to turn on the fan. Most people use a thermostst; I use a timer to get an early jump on moving the air out before too much heat buildup.
I would put in a radiant barrier on the underside of the roof rafters, from just above the insulation to about 1' below the ridge. You can order a roll from Solar Shield at 1-800-645-3645. An air staple gun makes the job pretty easy. You will be channeling the hottest air from attic floor to the ridge between the rad barrier and the roof decking.
If you have collar ties forming a triangle of space at the top of the attic, you can go across the bottom with the foil/paper barrier, and using some foil backed foam board, channel the air to the gable fan.
The idea,is to pull fresh air into the attic,up behind the rad barrier to the ridge area, and then out the gable vent via the fan. You may find that your attic with out this system is 140 deg +++, and with the system is about outdoor temp. That is just the temp improvement. You will also be avoiding the radiant heat gain which even penetrates insulation. (this is why the upstairs stays hot so long after the sun is down)
Now let's look at the air flow. Take a strip of tissue paper and tape it to one of the supply grilles upstairs. Turn the blower to "fan on". Fix the strip so that it flutters or is supported by the air stream. This is your visual indicator to see if you can make air flow improvements.
Remove all the supply grilles and using aluminum tape, seal any gaps between the sheetrock or floor and the duct work. You want a smooth air tight liner to prevent any air from blowing into the wall or under the floor. Don't overlap the tape beyond the border that the grille will hide.
At the air handler, you want to tape all the seams and connections. Feel for any air leaks, especially where the plenums connect to the air handler case. Now do the same procedure to the return side. Those returns in the bedrooms will probably have some gaps between the wall and the duct.
If you have return air filter grilles, you can remove the filter from the air handler and tape the panel door closed. Note, you must have filters in all returns before you can eliminate the one at the air handler.( Before taping the seams of the blower compartment, you can turn off the unit, including the breaker,open the case and inspect the blower vanes. After many years, they often build up a layer of crud that reduces their ability to scoop air. It is not difficult to pull a blower out and clean the vanes. If you do this, clean all the vanes to maintain balance.)Check for oil taps while in there.
Tape the seams on the air handler that are on the return end. You won't be able to feel air blowing out because that is the "suction or negative pressure" side of the blower.
With the system tight and well fitted to the house interior, you have done about all you can for air flow. The tissue strip should show greater action if you made any sealing improvements.
Check the air temp across the cooling coil in A/C mode. I use a couple of $10 digital thermometers with a 10' wired sensor from Walmart or Target. Put a small hole in the return plenum and in the supply plenum and stick the sensors into the air stream about 10". With the unit cooling, you should find about a 15 deg or greater difference, unless it is very humid in the house. You may find as high as 20-22 deg. This is a rough test to see if the refrigerant, compressor etc are correct.
I trust you have checked the tightness of windows, doors, access to the attic etc. Are you supplying out door air to the clothes dryer, gas water heater and gas furnace, and keeping that air from joining house air? Isolate those appliances so that they are not sucking conditioned air out of the house, or causing backdraft from the flues.
There are a number of other things to do, but these should make an improvement and save some energy cost both cooling and heating.
Please let us know how this turns out. You are not the only one to have a hot upstairs. Good luck PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Really appreciate your help, Paul. I'll probably get cracking on the fan end of things in the early Spring before it starts to get too warm.
I'm heading to the bookstore tonight to look for your book.
Paul, very interesting info in that post.
You have 833 sq ft per ton of A/C capacity. That is a stretch for most houses on hot days, unless very tight and well insulated. By tight, I mean both the house envelope and the forced air system.
If I recall, he's fairly northernly -FWIW, in my area 3 ton is what I expect to see on that size and age of house.
_______________________
Albert Einstein said it best:
“Problems,” he said, “cannot be solved at the same level of consciousness that created them.”
Your mileage may vary ....
Bob, he is north, and I hope he can get by on 3t. I have a bunch of clients in NJ with houses in the 2800 sq ft at 4t and 3500 at 5t. Single systems for whole house, air handler in the basement, and hot upstairs. Houses only 6-7 years old with thermo windows, a lot of attic insulation, and billed by the builder as "energy efficient" construction. They are having the same problem, hot upstairs, and freezing basements. After better sealing,and pulling down the attic temps under the black roofs, we can usually get enough cold air to the upstairs by seasonal changes to the dampers. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Bob. a theoretical concern is that a power vent might leave areas of the roof sheathing in "still air" which can lead to condensation problems (even in summer! - get super saturated humid air up there, sun foes down, roof cools down -voila! condensation.)
I can'tr say that I've seen any attics which actually (and obviously) have had that problem.
A whole house fan is generally used at a different time of day and for a differentr purpose.
Albert Einstein said it best:
“Problems,” he said, “cannot be solved at the same level of consciousness that created them.”
Your mileage may vary ....
There are two types of 'attic fans', at least I've heard people call both types 'attic fans'.
One goes on the gable end, and exhausts hot air from the attic, on a thermostat. The other kind pulls air through the house and into the attic, to cool the house with outside air.
I have both types, and the first one I highly recommend. Even with a ridge vent and clear soffit vents, my attic was getting > 140 in the summer. The ceiling underneath was noticably hot. The gable end vent went in pretty easily and keeps the attic cool, which keeps the house much cooler.
The other type, which is installed in the hallway ceiling, blows air up and out, theoretically cooling the house by pulling in cool nighttime air. My attic roof is probably only 4-5' high at the peak and I think there's probably too much back pressure, because the fan is loud and pulls a vacuum, but doesn't do all that much cooling. It's also expensive to run. I also had to build a custom insulation cap for keeping the cold air out of the living space in the winter.
Remember to put a high-temperature cut-off switch in-line with either type of fan - you don't want it to turn on and feed a fire!
Many of the problems you mention with your whole house fan can be eleviated by getting a Tamarack fan instead.
Part of the energy savings comes from running the AC a lot less.
Wow, they look nice.
for others:
http://www.tamtech.com/hv1000.htm
It might be worth saving up for one of these, even though it's about 6x the cost of the one I got.
They have to sell direct for full retail. Some of their distributors do sell them for less than MSRP.
Not saying they are cheap, just less expensive...