HVAC and/or attic ventilation

big2bird

big2bird

Charter Member, Founder Bird-Run, Cruise-In Bird-R
Joined
Mar 5, 2008
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Location
Anaheim, Ca.
Guys, my power bill is killing me. I just installed a SER13 gas package unit to replace my 23 year old unit. I replaced all my ducts with R6.5, and increased my gable vent sizes, but I'm on a mission. I want MORE.
Anybody know a no BS site on attic ventalation. There seems to be TONS of hype and BS with no science out there.
I also have a few questions to a HVAC ENGINEER. I'm really getting into this now. I need a working knowledge of schedule J, S , and all that crap.
Being an electrician, I know from experience that a little knowledge can be dangerous. I do want to learn what I can though.:D
 
How many gable vents you have?? two?? I would put a fan in each one, something not too powerful as it draws too much current...

I would do the same, but I have a mansard roof which I hate, and it's got ridge vents in it....not that they do a damn bit of good, primarily because the nitwits that did the plastic soffits just put the vented plastic over top of the wood with holes/screens...so therefore blocking any good done from the vents....

it's hottern' HELL up there.....

I had great luck in Md. years ago with a townhouse 3rd floor bedrooms hot as hell...put in the attic vent flying saucer, and must have dropped that temp up there by some 20f....IN THE BEDROOMS>>>>
 
When I built my garage I put two of the thermostatically controlled fans in. They worked for about a year and quit just like all the modern SHIT you buy.

If I was doing it again I'd avoid any powered option and look to the spinning whirlybird things or something a bit more benign than the stupid electric pieces of garbage. But then, Chinese folk gotta eat too...:suicide:
 
You need intake vents as well as exhaust vents for best ventilation. When my house was built the builder had installed plenty of roof peak vents to exhaust the air but nothing down below to draw it through. I went to one of the building supply stores and picked up 8 of the 16" x 8" soffit vents for about $2 each. Pretty easy to cut a hole in the soffit and install 2 on each side of the house. Lowered my bills at least $5 per month in the summer. Not bad for a $16 investment.

You can also get some 2" round aluminum soffit vents at Lowes pretty cheap. I think they were about $10 for a bag of six. Pretty easy to install with a 2" hole saw. They just pop into place.

For best results, you need the same cross sectional area of intake ventilation as you have in exhaust ventilation.

I've got an attic ventilation brochure at work someplace. I'll see if I can find it and copy it for you.

You might see if there is a state energy efficiency agency in California. If so, they might have the info you need on their web site.

DC
 
I was just looking into this over the weekend (yeah, I know, I have an exciting life).

I don't know if this is just the midwest but the word I got was:

For every 300 sq/ft of living space you need 1 sq/ft of vent with 60% of that from the soffit vents.
 
Adding insulation around the AC ducts is the first step in the right direction... what's up there is just enough to meet code requirement, nothing else.... add insulation to the ducts and the floor (ceiling) and you'll see a difference on your monthly bill...
 
MYBAD79 said:
Adding insulation around the AC ducts is the first step in the right direction... what's up there is just enough to meet code requirement, nothing else.... add insulation to the ducts and the floor (ceiling) and you'll see a difference on your monthly bill...
Click to expand...

I already have R-30 insulation in the attic, and just reducted the whole house in R6.5 flex duct.
 
BBShark said:
I was just looking into this over the weekend (yeah, I know, I have an exciting life).

I don't know if this is just the midwest but the word I got was:

For every 300 sq/ft of living space you need 1 sq/ft of vent with 60% of that from the soffit vents.
Click to expand...

That's the basic building code I came up with.
 
DC3 said:
You need intake vents as well as exhaust vents for best ventilation. When my house was built the builder had installed plenty of roof peak vents to exhaust the air but nothing down below to draw it through. I went to one of the building supply stores and picked up 8 of the 16" x 8" soffit vents for about $2 each. Pretty easy to cut a hole in the soffit and install 2 on each side of the house. Lowered my bills at least $5 per month in the summer. Not bad for a $16 investment.

You can also get some 2" round aluminum soffit vents at Lowes pretty cheap. I think they were about $10 for a bag of six. Pretty easy to install with a 2" hole saw. They just pop into place.

For best results, you need the same cross sectional area of intake ventilation as you have in exhaust ventilation.

I've got an attic ventilation brochure at work someplace. I'll see if I can find it and copy it for you.

You might see if there is a state energy efficiency agency in California. If so, they might have the info you need on their web site.

DC
Click to expand...

See, I need more intakes, but the house is stucco with no soffits. The eaves are bare up to the walls, then stucco with blocking behind that between rafters. Could get REAL ugly to retrofit some more.
 
GT6Steve said:
When I built my garage I put two of the thermostatically controlled fans in. They worked for about a year and quit just like all the modern SHIT you buy.

If I was doing it again I'd avoid any powered option and look to the spinning whirlybird things or something a bit more benign than the stupid electric pieces of garbage. But then, Chinese folk gotta eat too...:suicide:
Click to expand...

Same story. Meager results, with 3 years of life, while also paying for power. No more. I bought 3 new ball bearing aluminum whirlybirds tonight, and that brings my exhaust up to double code. Now, to add some intakes in stucco.:suicide:
 
What about the walls of your house ?? Insulation quality on the walls makes a huge difference - ever got that checked out ???
 
I also need to know the truith about radiant heat barriers. They look promising, but the roofers say it decreases shingle lifespan. My roof is new, and that is not desirable. They also require ridge vents, but some say they don't work as well as they claim.
 
MYBAD79 said:
What about the walls of your house ?? Insulation quality on the walls makes a huge difference - ever got that checked out ???
Click to expand...

I have also retrofitted all walls but one bedroom with R-13, along with increased shear walls and anchors for seismic.
And yes, the crawl space is R30 also.
My immediate concern is the attic temps.
 
big2bird said:
I also need to know the truith about radiant heat barriers. They look promising, but the roofers say it decreases shingle lifespan. My roof is new, and that is not desirable. They also require ridge vents, but some say they don't work as well as they claim.
Click to expand...

Well, my roofer called tonight, and said go ahead with the radiant heat barrier. Sounds cheap, and worrks well. However, ridge vents suck. He said the originator went belly up from lawsuits over roof leaks, and that crows like to bite them up for nesting material.
I think I'll try the south facing side, and see how it works. easy enough to tear back out. $78.00 for 48"x500' at the Home Dump.
 
Minimum code (well maybe not CA code, but everywhere else) is with high (peak) & low (soffit) venting, one square foot of vent area for each 300 square feet of conditioned space attic area (if I remember right this late at night). That's minimum. And remember, "Built To Code" means built to the absolute minimum standards the law will allow...

The spinning turbine vents 'work' on the principle that the convection draft will get the turbine spinning which will then draw more air out. Think about your work/power engineering principles .(Where's Turtle when we need him? Where is Turtle, by the way??) You use passive airflow convection currents to spin a mechanical device to thus draw more airflow....Hey, buy two and I'll toss in a free magnetic ionizing fuel filter for your car guaranteed to improve milage & performance by 20%! All those fucking things are good for is to keep the neighbors awake all night when the bearings go bad and they start sqeaking.

No soffits, huh? bummer--where's you passive shading? Oh well, moot point. Install regular roof vents down low as possible without being blocked by insulation, and more up high. For HVAC generalities, you want twice the area of return than you have for supply--supply is higher pressure (forced), return is low pressure (passive). Same principle here---install as many low vents as you can (I don't have any numbers to give you, but I'll just toss out a combined total of 1 sq foot of vent area per 50 sq foot of attic area--more if you want--I know I have more than that in my little house) ) and then install at least 1 1/2 times MORE area of high vents as high up on the roof as you can than you have in low vents. The more airflow you have, the better. Put a few more low vents on the cool side, more high vents on the hot side of the roof. Enhance the convection effect.

Gable vents can help, especially if aligned with prevailing winds. Increase the size of your gable vents--make 'em as big as you can, get a breeze flowing through the attic! And/or an attic exhaust fan with thermostatic control can help a lot too. Again, exhaust (fan) on hot side of house, intake on cool side. And don't whine about service life---christ, any mechanical device has a service life (hence, the emphasis on passive ventilation). Do you bitch about how long the water heater, furnace, A/C last (Well, OK, yes we all do). How often do you service & repair those dam mechanical beasts we call 'cars'? How much do you bitch about that?:D

I don't know how tall your attic is, but if you have R30 in it, well then add more---keep the heat away from the ceiling to reduce the broiler effect. Just don't let the insulation block the ventilation airflow.

You want to insulate the conditioned space, not the roof deck itself. Don't cook the shingles from below with reflective barrier directly under the roof deck. Let the heat absorbed by the shingles pass through and then be removed by being transferred to the medium of the attic air which is then removed by ventilation. But isolate that heat from the conditioned living space below.

R6.5 duct insulation is better than nothing, but any A/C or heat equipment & ducting in an attic (whether California or Minnisota) is pretty fucked. Hells peckerwood, how do you think the efficiency of the A/C coil is affected living an environment like that? Again, moot point. You got what you got. Cover the ducts with more batts to increase the insulation. Flex ducts have a very poor airflow rate compared to hard tin ducts, therefor the air flow is restricted & slowed down, thus increasing its absorbtion rate of surrounding heat, and thus doubly reducing its efficiency in cooling the conditioned living space.

What color is your roof? Dark colors absorb heat, light colors reflect it thus reducing the heat absorption of the attic space. Moot point #3......


So, to wrap up Johnny's presentation, the main points are:

Increase ventilation in the attic airspace (and then double it).
Increase insulation to the conditioned space & eqipment (and then double it).

Just get up really early when it still cool up there to service the attic fan, just as you periodically clean the A/C condenser, change the furnace filters & and check the fluids & shit on the cars.....


Schedule J and all that stuff I haven't gotten into.


And here's a website from aguy whom I have met in person and he's exactly the kind of man who would fit right in here on VetteMOD, or any construction sight---even theough he is an 'engineer'. He even makes fun of himself for that. I'm too tired right now to look for any specific articles so I'll have to leave it up to you look for them, but I know he has at least one about attic HVAC, and others about roof/attic/conditioned space relationships. (edit: If he contradicts any of my opinions above, listen to him, not me!)

http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1






Check out his other articles in the sidebars under "Digests", "Insights", & "Primers" as well--he's not only one smart motherfucker (and he'd be honored to called that) but he's a hell of a good & humorous writer as well.
Here's some more samples:

What do the American Revolutionary War, whiskey & NASCAR all have in common with building practices?
http://www.buildingscience.com/docu...on/?topic=/doctypes/building-science-insights

"Top Ten Dumb Things to do in the South" HVAC-wise
http://www.buildingscience.com/docu...th/?topic=/doctypes/building-science-insights

Let's make a model space shuttle from a brick, a cold beer & two cigars...
http://www.buildingscience.com/docu...ce/?topic=/doctypes/building-science-insights
 
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Are you SURE its all the attic? Window glazing up to snuff? Its an electric power bill - do you have gas on the Hot water heater - or electric. Unless its an "on demand"" -- $$$$. Insulate the case of that one too.
I chased some of the same a couple of years back. Added the foam rafter "doofers" that span between the trusses at the soffet to ensure there is ventilation -- then shot 1/2 the attic with a ton of cellulose. Seems to have made some difference -- but now - no storage space. Well, guess if its in the attic - I don't need it all that bad anyway.

Best of luck on chasing the problem.

Cheers - Jim
 
It's pretty hard to make drastic improvements to an existing design and without gutting the house, only general guidelines will help. Only you can decide what will end up being cost effective.
Be aware that a SEER 13 rating for a couple of years has been the absolute minimum rating and that higher top rating seer often is not recoverable financially in the life of the unit. I know a lot of units work afte many years, but the efficiency of the condenser coils after 10 to 15 years are a small percentage of what they were when new and the unit will run a greatly reduced capacity. Keep in mind the rating was done under lab conditions. Installation results do vary.

A package system is not a really efficient design, and I understand you are stuck with that. Hopefully it is a ground unit and not a rooftop. The biggest proglem is with those is the plenum ductwork both inside the unit and the run to the main duct system.
You can add thin foam insulation inside the unit (careful of waranty) and thick rigid foam (ie. 3") glued and sealed to the outside of the plenums.
On the plus side of a package unit, there is no reason for an installer to touch the refrigerant charge, so it should be correct. Residential units are often not charged properly and result in up to 30% in energy loss.

Attic temp makes a big difference.
Here we commonly use a full continuous 4 or 5" soffit vent around the complete soffit.
Without seeing pics, I hope I understand your soffit properly, but remove the stucco and blocking between the trusses (rafters), top plate and roof sheathing, and install a full soffit vent, such as those used with aluminum siding. PITA messy job, but a diamond blade on a 4 or 5" grinder works wonders. The vented soffit installs on the bottom of the tails, netween the fascia nd the wall, so any stucco damage above the top plate won't be seen.
Don't know what type of roof you have, but on our rentals, as well as ours, I put a white elastomeric rubber coating on the concrete tile and also on a shingled house. I did it to prevent reroofs (they will last forever with repainting), but on a shingled house it dropped the attic temp by 40° mid day by itself. Solar radiation is high in S Florida. I've been in attics as high as 145°.
If your ductwork is in the attic, it makes a big difference, especially when the system is idle and convection is heating up the ductwork.
Your looking for the canopy effect. Cool and breezy.
You must be carefull to not have your ductwork sweat in an attic, ideally all the ductwork should be in air conditioned space. That alone can save a bunch.
You can also get paint for your outside walls that has ceramic particles mixed in, (just like headers) and the reduces the radiant heat by a good percentage.

If you have a pool, you can add a water to refigerant condensing coil to the condensing side and use the superheated rerigerant to heat the pool and conversely the pool will drop the refrigerant pressures. Same principal as a pool heater, but it uses free electricity. On mine it dropped the condensing unit amperage draw by 3 amps, a direct electrical savings and also dropped the compressre head pressures translating into a longer lasting compressor.

Shade all your windows with awnings or at least reflective film etc.
For example, adding an 8 ft wide unshaded slider to a west facing wall here, required 1 more ton of a/c to cool the house. That is a lot and shows what the sun can do.
This was discovered by using a heat load program developed by Trane and accepted by Florida codes for design.
I still find this unbelievable, but wall insulation makes a bigger difference than attic insulation. Studies from Trane have proven that and is incorporated into the program.

Use a good programmable electronic tstat. Probably save the cost of it the first month.

Keep in mind, most of this code stuff, especially for structures, is just a minimum requirement, you can usually improve on it substantially.

Good luck figuiring the cost effectiveness. :D
 
My house is on a crawl space and its pretty cool in the crawl even on hot days. I thought I would try to take advantage of that cooler air and use that air to force the hot air out of the attic. The furnace room is in the center of the house so I ran an 8" diameter tube from the crawl space directly up in to the attic with an 8" diameter solar powered fan inside the tube. I found the 8" heating duct tube and the fan and solar panel at a garage sale but I'm sure new this couldnt cost more than $100. I reduced the attic temperature by 15 degrees. I would think tweaking this idea you could do much better,the cooler air in the crawl space is free.
The very little tweaking I did: Iniatally the 8" tube went just inside the attic and was at the ceiling in the crawl space. I extended the attic tube to go higher so the cooler air could fall and mix more with the hot attic air and force it out the vents more. I also extended the tube in the crawl space to go closer to the ground thinking that air is cooler. I did these 2 things at the same time but I think the attic extension was the real improver.
Initially the temp drop was 10 degrees but went to 15 after the extensions.
I monitored the temp drop with and old inside-outside thermometer that I buried in the insulation in the attic.
 
Don't know if this has been covered in this thread but on a hot summer's night what would you normally like to have the attic temperature to get optimum results from your home A/C unit. I have a 2 story house and when I walk upstairs I can start feeling the air temperature increase. I believe the attic temperature has a lot to do with it so I installed a attic fan with a thermostat I just need to set the proper attic temperature which I figured around 100 degrees before the attic fan turned off.
 
My neighbor and I have been thinking of rolling several cans of Cool White roof coating/sealant on to the shingles, years ago I bleached them and got good results, this year it's marginal for some reason....they are normal shingles with the white/lt. gray gravel on them....just replaced the rolled roofing on my nearly flat roof room addition....white metal this time around....

I dunno how it would look from the street though...but on the backside, who cares?? it virtually can't be seen....:smash:
 
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