# A/C Ducts in attic - Repair or Replace?



## TexasFlats

30 year old house and $700 a month summer light bills, so I started poking around to see where the money was going. I have rigid ducts with fiberglass/aluminum foil wrap insulation on them. After cutting away the insulation in a few key places, I began to see what the problem was...
huge gaps at every place where there was a joint in the duct. Return air wasn't sealed, not enough insulation in the attic, not enough ventilation, etc., but I digress.....

I have been told by a couple of a/c guys that I should keep the rigid duct. However, all the insulation will need to be removed, ducts sealed with mastic and reinforced tape (not "duct" tape), then reinstall the insulation - which is inadequate and needs to be upgraded. All this and the inside of the ducts will still need to be cleaned, and I'm not real thrilled with how the ducts are routed in the attic anyway.

Seems like it would be easier and more cost effective to demo the old ducts and replace with flexible ducts: they will be new and clean, have better insulation, better routing in the attic.....

It sounds like I have answered my own question, but why are the a/c guys so adamant about keeping the rigid duct?

Also - where can a regular guy like me get duct fittings & hardware? Seems like the big box stores don't have everything I'll need, no matter which way I go.


----------



## Team S.A. Blue

*ducts*

Most 30yr old houses i see with round duct are set up for heat only and then a/c is added. So make sure the duct is sized right. The air flows better with round pipe thats why they want to keep it.
Its just labor to replace and wrap because the pipe is not that expensive.
Where do you live


----------



## TxDuSlayer

You can get some duct stuff at Home Depot! You can also get duct work, collars,flex duct from johnson supply, grainger, johnstone, & some of the smaller a/c supply shops!


----------



## xtreme

Don't put flexi duct in your attic. Rigid is better but the flexi is cheaper


----------



## RB II

Is the rigid duct, duct board or metal? I assume duct board. If so and it's 30 yrs old, I would replace it. Resize to match surrent conditions. After the new ductwork, add insulation, etc. While metal duct is the best, it is way expensive and I wouldn't have duct board. Not sure why flex duct is not good, as stated above. Impractical to not use flex, at least on the drips to the registers (used every day in commercial work). As long as it is properly supported, it will provide years of service and air flow won't be restricted. At $700/month electric bill you can spend a lot to fix the problem and get it right.


----------



## TxDuSlayer

Flex duct is fine to use. A $700 a month light bill, have you replaced your a/c system yet? That is where you will see a tremendous amount in savings, replacing your leaking air ducts will help as well. It made a tremendous differance at my house.


----------



## cuzn dave

Might want to check on city and fed tax incentives for energy conservation updates.


----------



## Mont

> It sounds like I have answered my own question, but why are the a/c guys so adamant about keeping the rigid duct?


It's nearly impossible to get rigid duct in an attic to meet the energy code. The new R-8 flex duct is the way to go. It's seamless, doesn't leak air and with r-8, it doesn't lose or gain heat. We ran sheet metal for 25 years and won't touch it anymore. A properly installed r-8 duct system will have less than 5% leakage. A "tight" metal system will leak more like 20%. Anyone that claims metal duct is somehow superior is living in the past.


----------



## TexasFlats

Mont said:


> It's nearly impossible to get rigid duct in an attic to meet the energy code. The new R-8 flex duct is the way to go. It's seamless, doesn't leak air and with r-8, it doesn't lose or gain heat. We ran sheet metal for 25 years and won't touch it anymore. A properly installed r-8 duct system will have less than 5% leakage. A "tight" metal system will leak more like 20%. Anyone that claims metal duct is somehow superior is living in the past.


The SilverBack has spoken... and my suspicions have been confirmed by an expert. Thanks, Mont.

TF

.


----------



## thabeezer

I was in the same position as you 2 summers ago and decided to have all of the old rigid taken out and the new duct put in..I read many message boards arguing one way or the other.

I replaced everything (ducts and outside unit and added return air) and I went from 500-600 a month electric bill in the middle of summer to a 300-350 electric bill.


----------



## DeaconDon

*Flex Duct*

I was a mechanical contractor for over 35 years. Originally, round metal ductwork, properly sized, sealed and insulated was the most efficient. Then, flex duct came into the market and at first we had problems with the exterior insulation deteriorating. In addition, a lot of contractors didn't install it properly, leaving kinks and bends as well as just laying the duct on the floor of the attic. The metal support in the ductwork is like a slinky and created ridges inside the duct... all of these things created a lot of energy loss. 
The new flex duct is much better and is well insulated. The exterior insulation wrap holds up well and, if the ductwork is properly installed (pulled tight and supported) you will have an efficient duct system. Of course, the ducts, plenum and return should all still be sealed to avoid air loss.... If I were installing a duct system in my own home today - I'd use the flex. Hope this helps...


----------



## Mont

I can't say enough good things about adding return air inlets. If you doors close themselves when the a/c fan is running, that room needs a return air added to it. I recently added 2 more returns bringing my total to 4, and it was amazing the difference before and after.


----------



## txhoosier

*tips/suggestions/supplies*

Any tips, tricks, orsuggestion as well as suppliers of material to add the returns??

thanks!


----------

