# Need ductwork replacement advice.



## missdoc77 (May 17, 2011)

Our current ductwork (all in the attic) is probably as old as our house, built in 1984.  The plenum is metal and the rest is insulated flex that leaks.  We attempted to tape/seal everything seveal years ago but all the flex needs to be replaced.  At some point in the next couple years we will probably replace the A/C and furnace, however, we'd like to get the ductwork done and add insulation first.  So my 1st question is this: if we simply replace the flex with an equivalent to what's currently there, will it work with the new A/C and furnace that goes in later?  In other words, is ductwork "standard" as far as fittings, etc?  

2nd inquiry: Should we be considering changing any of the duct sizing for any reason?

3rd: Should the plenum be insulated?  If so, how do we go about insulating the current plenum?  We don't plan replacing that if we don't have to.  As far as I know, there's nothing wrong with it.

I hope that makes sense.  This is our 1st HVAC project so doing lots of homework!


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## nealtw (May 18, 2011)

I would talk the the furnace people for what they think. They can check out the house for what you need. Then you will be ready for the AC and furnace.


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## missdoc77 (May 19, 2011)

The furnace and a/c people want to sell me their product and services, not give out advice on how to do any of it myself... so I was hoping to get some unbiased opinion/advice through a forum such as this.  Thank you for the suggestion, though.


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## nealtw (May 19, 2011)

Get a couple DETAILED quotes for that new system.


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## missdoc77 (May 20, 2011)

I appreciate the input so far but was really hoping to get answers to my actual questions.  I thought that's what this forum was for.  I've received quotes and as detailed as they come... they don't answer what I'm asking here.  So let me try again:

#1 - Is ductwork "standard" regardless of brand or type of replacement a/c and furnace?  i.e. Will the old ductwork fit the new system?  And vice versa, if I replace ductwork 1st, will it work with any system I purchase?

#2 - Currently we don't have any major hot/cold spots.  So if we replace the current ductwork with the same type and sizes, etc. will that be sufficient regardless of what new a/c and furnace go in later?

#3 - We do not plan to replace the existing plenum.  It is metal but not insulated.  Should it be insulated for greater efficiency??  If so, what kind of product is recommended for doing so?


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## nealtw (May 23, 2011)

google: "duckwork sizing"


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## missdoc77 (May 24, 2011)

Ok, I'm gonna pretend that you're joking.  Google is the 1st place I visited.  I did not find the answers to the questions I KEEP asking here...  please, if you don't have a constructive and/or informative answer, don't bother.  



nealtw said:


> google: "duckwork sizing"


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## oldognewtrick (May 24, 2011)

Missdoc, i think what Neal is trying to tell you is that HVAC systems are unique to each dwelling and are sized by trained technicians for load requirements. You will probably not find a generic listing for what you are looking for. Climate, insulation, amount of glass area, window and door openings and type of construction will factor in what is going to be required for a functional system.

HVAC and electrical systems are better off left to the pros for the first time DIYER. Don't get me wrong this site is devoted to the DIYer, but with HVAC and electrical you are getting into systems that can kill you.

Welcome to the site and we hope we can be of help.


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## inspectorD (May 25, 2011)

Our current ductwork (all in the attic) is probably as old as our house, built in 1984.  The plenum is metal and the rest is insulated flex that leaks.  We attempted to tape/seal everything seveal years ago but all the flex needs to be replaced.  At some point in the next couple years we will probably replace the A/C and furnace, however, we'd like to get the ductwork done and add insulation first.  So my 1st question is this: if we simply replace the flex with an equivalent to what's currently there, will it work with the new A/C and furnace that goes in later?  In other words, is ductwork "standard" as far as fittings, etc?  


 No ductwork is sized for the heat loss on a home and the system.is installed to not be oversized. We don't even know if the system that was installed was even correct in the first place, and with added insulation, it may cut down on where the ductwork actually needs to go.



2nd inquiry: Should we be considering changing any of the duct sizing for any reason?

We have no idea from here.



3rd: Should the plenum be insulated?  If so, how do we go about insulating the current plenum?  We don't plan replacing that if we don't have to.  As far as I know, there's nothing wrong with it.

Yes it should be insulated on the supply side for loss. Use insulated ductboard sold at A/C supply houses.




I hope that makes sense.  This is our 1st HVAC project so doing lots of homework![/quote]

Hire a pro to at least consult with you on your home. Even if you do all your homework and attempt DIY, you will miss something and it will still cost you.
And everybody here just wants to help. Treating them like children doesn't help anyone.
If this did not help, move on.


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## missdoc77 (May 25, 2011)

Thank you, old dog and inspector!!!  Finally some reasonable answers that don't treat ME like a child!  I may be a girl but I'm a very capable one and have already done a lot of home improvement jobs.  Telling me to "google it" or just "hire somebody" is what's childish.  I have full faith in my ability to properly do this project.

Inspector, our current system heats and cools fairly evenly throughout the house.  I guess maybe I'm not wording my question to make sense... my concern is basically whether or not an equivalent to what is currently there (ductwork-wise) will work with the new units that will go in later.  Guess that's not possible to answer without more info??  As far as adding insulation, our attic is very poorly insulated so AFTER new ductwork goes in, we will be blowing in insulation to bring it up to par.

Old dog, thanks for your input.  We're not messing with electrical ourselves.  The new a/c and furnace appliances will be installed by a pro but we must save some money somewhere so will be replacing ductwork ourselves.

I've had two quotes done and neither person wanted to really answer my questions... obviously, they'd rather us pay them to do the work so it's frustrating trying to find solid advice.  I do know an a/c guy that's a friend of the family, just impossible to get him to our house, hence turning to this forum.   

My intention was never to "treat anyone like children"... but coming to a DIY forum then being simply told to hire a professional or google for answers is downright belittling and a waste of time.  Anyway, again, thank you for the help.


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## inspectorD (May 25, 2011)

Your welcome

And you may not have had the right company come out to look. Most good quality companies want to educate their clients, and some will even let you do the ductwork yourself. But only after they size up and do load calculations for what you are planning. 
From here there really is no good advice on sizing until you have someone farmiliar with your house look at it.

Chances are it could be fine, but I would still ask a professional opinion. Let us know what they say.


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## nealtw (May 25, 2011)

Missdoc:
 I am sorry for hurting your feelings and was not joking. When coming to sites like this you have to remmember that advice is worth what you pay for it and opinions are like heads: everyone has one. That's not to say there isn't a lot of good information here. As a home owner or diyer you want to use this site for ideas and the language that other people use so that you can then look things up and learn a little, so you can hold your own with the pros. This what I do and I just assumed others did too. 
I relly am sorry.
    Neal.


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