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Coil Material Opinions:

Call me a professional homeowner.

I am going to have the flex duct in my attic replaced because it is vintage 1982, and on much of it, the cover has split and come off. Its all in an unconditioned space.

The question: The units were replaced in 1996 with a Ruud unit and works well. But it is getting old. I asked about replacing it. There are "issues" because it is in a closet and a 16 SEER unit is too high etc. But in discussion with the person looking at it, he stated that his company uses a well known brand that is too high to fit under the door header. There's a water heater under it. But his brand uses  all aluminum coils while the other ones use aluminum and copper. And that all those solder joints were sources of leaks while a straight continuous piece of aluminum tube had less places for leaks. Therefore, what they proposed was better.

Being a heater, I've put in a lot of copper/aluminum coils in and I've not seen a lot of them leak, if any at all.

I'm not in any way questioning the integrity of the person or the company. I'm just asking the experts here what they think.

Is it any kind of code that you MUST use R-8 flex duct in unconditioned spaces? I don't know what they propose to use because the quote isn't broken down. I read somewhere that it is. If they can, I will request R-8.

I've already figured out that if possible, I'd try to see if the unit could go in the attic. But that's another issue. I'd rather have it in the conditioned space in the closet.

Any comments will be appreciated.


  • SpenceSpence Member Posts: 316

    Following all of the storm damage before Sandy, we had the now-famous "Chinese Drywall Era" which drove most manufacturers crazy. Hence, the movement to all aluminum coils, which appear to be less prone to off-gassing building materials creating champagne leaks in coil tubing.

    R-8 duct insulation in non-conditioned spaces is code. However, check your local AHJ to see if they have a different requirement.
  • icesailoricesailor Member Posts: 7,265
    Insulated Coils:

    Thanks for the info.

    Everyone gets nuts over AL. Where I used to live, AL TV antennas didn't last long and on houses, carpenters always used zinc flashing's on exposed to the weather locations. Like over windows and doors, cheek flashing's. Never use anything but zinc. But I used to find eaten away zinc all the time. I bought a house on Cape Cod that was built in 1972. Racoon's tried to get into the attic through a wall cheek. I re-shingled it and the aluminum flashing used like it was 1972 and just off the roll.

    As far as the R-8 Flex Duct, I read somewhere recently that they, professionals installed R-8 in unconfined, unconditioned spaces as it was code. That if you wanted R-8 Flex Duct, you had to go to a REAL HVAC Supply house that stocked it. The DIY and work out of their van clan, go to Home Depot or Lowes and the only flex duct they carry is R-6. So, I checked Home Depot and Lowes. That's all they carry, R-6.

    I am having the flex duct in my attic replaced because it is 1982 vintage R-2.5 and the covering has all come off. I asked the contractor about using R-8 in the conditioned space (like we do in Massachusetts) and it was like he asked him to donate his first male son. He called me later and said that none of his suppliers carry it and it would have to be special ordered. It was my understanding that it was a DOE requirement and part of any energy improvement you did.

    Its just another government conspiracy.
  • TonySTonyS Member Posts: 849
    Rip it all out

    Put in some new inverter mini splits. R8 for air temp of 55 and attic temp of 120 thats a 65 degree delta t. They require more in a wall thats a 20 degree delta t.

    I did it in my place and it cut my bill in more than half.
  • SpenceSpence Member Posts: 316
    Rip It

    Your post certainly strikes a chord to those of us who advocate locating ducts in conditioned spaces, which I view as an underlying tone of your comment. In some applications, cost or physical limitations get in the way of doing the right thing; keeping ducts out of attics.

    Your post also nods toward the value of insulation. Using your Delta T, a 6" duct would lose 15 BTUH per linear foot with R8 and 11 BTUH with R10, so if you aren't able to rip and tear then insulate, insulate, insulate.
  • icesailoricesailor Member Posts: 7,265
    Unconditiioned space duct:

    I don't know if your comments were directed at me.

    My Condo in FLA was built in 1982. On a slab. The condenser is inside the conditioned space. The insulation/flex duct was probably R-2,5. I covered most of it with 6" fiberglass insulation to help it. A few weeks ago, when it became cool enough outside to go into the attic space, I found that a lot of the grey covering had split and fell off. I'd seen the same thing in the North where I worked. I wanted to replace all the flex duct. I wanted to replace it with the highest R Valve that I could get reasonably in.

    I know about the energy codes and HVAC, being a "Heater" myself. I'm a "Wethead", NOT an airhead. But I know the drill because of the turmoil that the airheads up where I work were going through. I've seen AC coming out of second floor ducts that in the summer, would have been perfect for January, and the air coming out in January would have been cold enough for July.

    I had them replace ALL the flex duct and Duct Board. Duct board was 1", now 1 1/4". I read somewhere on a forum about how the "Pro's" buy their HVAC materials from Professional Wholesalers. "Others" get it from Home Depot or Lowes. Where the thickest they stock is R-6. That the code requires R-8 in "unconditioned spaces". I asked about them using R-8 in the attic. They had never heard of such a thing. They asked their supplier (not H-D or Lowes) and they were told that they would have to special order it. So, I had to settle for R-6. Cost wasn't an issue for me. I just wanted it replaced. The whole thing was a mess. It works a lot better now.

    The coil issue came from a comment by the estimator. They used a certain brand/manufacturer for their equipment that is very well known. The selling point was that their coils are all aluminum and no copper. That aluminum/copper coils could fail. A Google Search for any brands all have a equal number of dislikes. Happy people don't write glowing reports about equipment. Unhappy ones write bad reviews. Any and all had plenty of dislikes.

    Then, there was the issue of locating a new unit to replace the 1996 Rheem that might on a good day be 8 SEER now. Their 16 SEER unit was too tall to get into the closet. Their 14.5/15 SEER would just make it because they had to install a filter rack on the bottom where as the Rheem had it built in. They were going to check to see if Rheem had a 16 SEER that would fit. I don't think that they did check because they are coming tomorrow to replace it. Who am I to tell someone how to do their job. It will be better than it was. Do I wish I could get a more efficient one in? You Bettcha.

    As far as the new Flex Duct, the old was all laying on top of the insulation. In 2006, I covered it all over with 6" Fiberglass batts. The whole thin flex duct was heavily insulated. The new installers made a point of hanging the duct up the floor. I guess that is standard practice. In my experience, it doesn't keep critters out of it. But you can cover it up a lot more with insulation in a unconditioned space. Now, I can't and the heat/cold loss will be entirely around the duct.

    What started this is that whatever the codes for "R" values in unconditioned spaces, and it needing to be R-8, it isn't being enforced in Florida. Because the Wholesalers don't stock it and the Professionals aren't using it. If the Hackaroos are only buying and using R-6 flex duct, they are setting the standard.

    I know that in Massachusetts where I worked, it was common practice to run 8"  R-6 in 2X10 Joist bays (9 1/4" high). When they started to require R-8, their portion of the world ended. The R-8 wouldn't fit without serious crushing and ovaling. Does that decrease the output?
  • SpenceSpence Member Posts: 316
    UC Ducts

    My comment was to TonyS (rip it) and was intended to be complimentary for recognizing the value of insulation. You mention two interesting issues: SEER and insulating ducts. First of all, if for example, your electric cost is $0.12/KWh and you have a 3-ton machine, a 14 SEER unit would cost $0.31/hr. while the 16 SEER model would be $0.27. Multiply that by cooling hours per season; you may find the small difference will make you feel better about not having room for the larger 16 SEER coil, and be better off having a well-performing duct system.

    Flex duct moves 40% less air than sheet metal, so any distortion makes a bad situation worse; especially if flex was not considered in the original design. Compacting insulation lowers R-value. However, it sounds as if you are trying to do it right. I would check your ESP to see the effects any duct distortion has had on your blower.
  • unclejohnunclejohn Member Posts: 909
    I thought

    The fan moved the air not the duct.
  • SpenceSpence Member Posts: 316
    I Thought......

    The blower has to overcome the duct resistance, plus the other pressure drops in the system, to deliver the designed air quantity. This is why many in the industry have the concept backward, residentially. You first have to find a blower that will deliver your required air, take out the PDs from your accessories, and use the remainder to calculate duct friction rate. A flex system will only increase the resistance against the blower, causing high energy use, noise, and substandard comfort, especially if distorted or not accounted for in the design.
  • icesailoricesailor Member Posts: 7,265
    Old Insulation:

    Everything was original to the place when built in 1982 except that there was some kind of a water coil to pre-heat the potable water in the water heater, All 240 units had them and they didn't work out. In 1996, they were all eliminated. We bought the place in 2005. What was here is what we got. I didn't want to change anything. But the duct work was over 30 years old, spliced in and broken and leaking. I was getting condensation out of some ceiling registers and staining the sheet rock ceilings. Just changing the duct work has been an improvement. Changing the rest while I can still afford it is a plus. I'd hate to have the compressor (R-22) croak in August three years from now.

    As far as the flex duct over square ducting, no one does it, the boarding is cheaper, and most wouldn't pay the price for square duct. As far as the thicker, if given a choice in pricing, thinner and cheaper over thicker and more expensive, if given a choice, a lot might pay the difference. Same with the R-6 to R-8round duct. If you never offer it as an alternative, and just have the attitude that "no one wants it because no one asks for it", then you aren't serving your customers well. I would have gladly paid for thicker insulation. I asked for it. They couldn't provide it. I can't make people do things that they can't or won't do.

    I had a customer that had built a new house by a "contractor" in the 1980's. It had a Carrier WA Gas furnace. The house was in a depression and got too hot in the summer. So, AC was installed. The old metal duct was replaced with metal duct with the insulation installed inside the ducts. It worked wonderfully. The owner sold the house in the late 1990's, early 2000's. The first thing the new owner did was call in a "AC Specialist". He said that the metal duct was junk and had to be replaced, that it would sweat and make a mess. It was all ripped out for 1" Duct Board. Only when he ripped out the old ducting did he realize that the whole job was insulated from the inside. The runs to the outlets were R-2 flex ducts. It was replaced with the same although R-6 was then available.

    Everyone has an opinion. Everyone has a better idea on how to extract cash from people. Some are better at it than others.
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