removing duct work from attic makes big difference to lower AC Needs

rollandelliott

http://www.nrel.gov/docs/fy10osti/48163.pdf

The above study proves what I have always thought. Contractors in the South USA are stupid for putting cooling systems in the attic. Also proves the two HVAC techs that said moving the duct work in conditioined space wouldn't make a big difference don't know their own trade.

Sad to see that as a society we waste thousands in efficiency just so we can save $500 in building costs up front.

I would seriously like to see a new building code that prevents new homes from having this. Wonder who I would talk to about that?

waynefromnscanada

Re: removing duct work from attic makes big difference to lower AC Needs

I discovered that on my own many years ago when I installed the central AC I used back in the day, and I'm no professional AC guy! Guess some folks just don't care about efficiency as long as they themselves are not paying the energy bill. Unfortunately, it also seems many homeowners are extremely short-sighted, preferring to save $500 now, even if it later costs them $5000 in extra energy.
Along similar lines here in Canada, it's common for large industrial, retail and office building AC units to also have built in electric resistance heat source to provide heat during the cold winter months, and to mount these AC units up on the flat roofs, then pipe the conditioned air down through the roof. The result? In Summer the AC unit is located and operating in the hottest environment possible, and in winter the built in electric heating unit is operating in the coldest environment available. The energy losses are staggering, but no one seems to either have their eyes open, or care about these situations. "It's always been done that way and it works, so why change". With that kind of thinking, it's no wonder North America is in trouble!

Toby

Re: removing duct work from attic makes big difference to lower AC Needs

I remember the statement "where were the adults when that building code decision was made" regarding HVAC ducting in the attic or crawlspace. Makes you wonder why we insulate walls to R20+ and ceilings to R50+ but R6-8 is fine for ducting moving your heated or cooled air.

waynefromnscanada

Re: removing duct work from attic makes big difference to lower AC Needs

Toby wrote: »

I remember the statement "where were the adults when that building code decision was made" regarding HVAC ducting in the attic or crawlspace. Makes you wonder why we insulate walls to R20+ and ceilings to R50+ but R6-8 is fine for ducting moving your heated or cooled air.

When the "professionals" installed the oil furnace in my parents home, their way of getting heat to the upstairs rooms was to punch a large duct right up through from the basement where the furnace was, up through 3 floors and into the attic. From there, they installed UNINSULATED ductwork around the uninsulated attic, like the many legs of a mutant spider that eventually turned down to deliver the air to the rooms ceilings. The air leaving the furnace was actually rather hot, but by the time it got to blow down in those upstairs rooms, it was still, well, maybe somewhat warm. No wonder they went through almost 1000 gallons of heating oil every year! In later years, I sealed off the supply to the attic and just let the warmth from the lower floor heat the upstairs. There was actually little difference in the comfort level, but a HUGE reduction in their heating bill!

rollandelliott

Re: removing duct work from attic makes big difference to lower AC Needs

What I found eye opening was the 15 to 20% savings. Why upgrade your HVAC to 17 seer unit when you can just move the duct work?

The issue is moving duct work AFTER the home is made is such a royal pain in the butt and expensive if you are not a DIY person.

Toby

Re: removing duct work from attic makes big difference to lower AC Needs

What's even dumber is when HVAC ducting is installed in the attic and crawlspace and you have a heat pump. I know, I'm living with that Trane Comfort Systems Specialists mistake.

rollandelliott

Re: removing duct work from attic makes big difference to lower AC Needs

if you can't move the ducts than consider buyrying them in insulation.
http://www.carb-swa.com/articles/guidelines/Buried%20Ducts_updated%203_17_2009.pdf
article goes over some of the basics of getting more effcient duct system in the attic. Renting a insulation blower is a day project and makes a lot of dust, but worth it.

Back to the original topic. I currently have some 6" diameter flex duct in my hot attic (28 square inches) . I'm assuming that if I replace it with 5x6 sheet metal ducts hidden behind drywalled chases that will be fine. I''ll need to make 2 to 3 elbow turns in the metal duct work which will cause a loss of air flow, but metal ducts don't have all the ridges of flex duct as well.

Is there any web site that goes over duct sizing?

LucMan

Re: removing duct work from attic makes big difference to lower AC Needs

rollandelliott wrote: »

if you can't move the ducts than consider buyrying them in insulation.
http://www.carb-swa.com/articles/guidelines/Buried%20Ducts_updated%203_17_2009.pdf
article goes over some of the basics of getting more effcient duct system in the attic. Renting a insulation blower is a day project and makes a lot of dust, but worth it.

Back to the original topic. I currently have some 6" diameter flex duct in my hot attic (28 square inches) . I'm assuming that if I replace it with 5x6 sheet metal ducts hidden behind drywalled chases that will be fine. I''ll need to make 2 to 3 elbow turns in the metal duct work which will cause a loss of air flow, but metal ducts don't have all the ridges of flex duct as well.

Is there any web site that goes over duct sizing?

Just Replace with 6" round pipe. Available in 5' & 10' lengths therefore a lot less joints for air leakage. Seal all joints with paint on duct sealer, or tape.

westbranch

Re: removing duct work from attic makes big difference to lower AC Needs

the tape you want to use is metallic, shiny SILVER metal foil with a peel off backing...

NOT the Red/Green stuff that is good for 200 mph, handyman special we are all used to...

TheBackRoads

Re: removing duct work from attic makes big difference to lower AC Needs

I can see this being done for warmer climates where you might not have a basement. We in the northern US do, so to hear of that in your attic sounds crazy tho I know they do. What happens when it needs to be replaced, do you have attic access that large?

ggunn

Re: removing duct work from attic makes big difference to lower AC Needs

TheBackRoads wrote: »

I can see this being done for warmer climates where you might not have a basement. We in the northern US do, so to hear of that in your attic sounds crazy tho I know they do. What happens when it needs to be replaced, do you have attic access that large?

FWIW, the systems are engineered so the pieces that need to be brought up will fit through normal between-the-joist attic access doors (we had our 25 year old system replaced a couple of years ago). As others have pointed out, moving the ducts below the ceilings in an existing home isn't really feasible, but our replacement ductwork is double insulated and buried in blown insulation.