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Old 04-25-2012, 04:51 PM   #1
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feasability of replacing AC flex ducting by myself?


so apparently the ducting in my attic is substantially leaky... to such a degree that i can actually feel cool air flowing down the attic and out the soffits that i was in process of replacing. from what i can tell several joints branching from a main rectangular duct are leaking, i suspect that they are responsible for the majority of that cold air i felt. i was aware of the poor condition of the ducting prior to this point... but honestly i had not thought it was as bad at this.

what concerns me however; having spent the last few days reading and researching proper residential hvac installations, is that the attic ducting is just garbage. nothing is strapped, the ducting runs over each other... theres alot of slack in the smaller ducts, and there are dozens of fairly bad kinks that ive been able to observe. i havent seen any mastic used anywhere, just tape and zip ties.

i had an HVAC company(apparently they only install trane products) come out last year to adress some minor issues. while they were there i asked if they could service the coil in the attic, at the time i was under the impression they needed cleaning somewhat regularly, it was my understanding at the time that it had not been cleaned in like 5 years. anyway they didnt seem to want to clean it, they actually said it appeared to be in OK condition along with the rest of the ac system. i asked if could give me a quote for just servicing the ducting. he hem'd and hawed for a while and i got the general impression that he didnt want to do it, but thought i personally should do something with it.

my question is simply... can a grown fat man about 300lbs 6'3" feasibly replace a small single story homes entire poorly constructed AC ducting with something far more appropriate for a 14 cent/kwh electrical service? its a fairly small single story cheaply built tract home built in the 70's , i think there are only 19 registers?
im mostly worried about what i should use to replace the main trunk line with and how to get it back into the attic, it looks like the existing one is just sheet metal? is that even possible? it seem like it would sweat badly..which is didn't appear to be doing. i cant actually get to it without hands and knees crawling and probably cutting some drywall. i understand that there is something called duct board that sounds like a suitable replacement, but can i work with it without specific tools? i have at a table saw and all the typical power tools, but nothing specific for sheet metal working.

anyway back to the original question. should i even bother trying? should i just fix what i can get to? if i can actually just blow out all the old duct work, is there anyway to do it in phases such that i can basically keep the ac functioning while i replace sections of the duct.
im going to buy the manual D and J books regardless so hopefully what ever i end up doing is done correctly.

thanks in advance for what ever advice you can give me.

edit: bad spelling, grammar etc.


Last edited by Queequeg152; 04-25-2012 at 04:56 PM.
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Old 04-25-2012, 05:24 PM   #2
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feasability of replacing AC flex ducting by myself?


I'm not certain ow physically fit you are. Just off the top of my head I've never seen anyone over maybe 200 pounds work an attic and even then they only do the equipment, not the ducts. One slip and you'll be on the living room floor not to mention if you become too hot and you can't get out in time, say you're in a tiny crevice on the back of the home and away from the staircase, and you're all alone and have a heat stroke up there than that's it, game over. You don't have to be thin or fat to have a heat stroke, many people have 'em in attics.

Infortunately, and please don't take this the wrong way, attic work is a thin and hopefully athletic man's game.

Your metal trunk line is insulated internally, why it's not sweating.

Duct board is very easy to work with but you may need to practice on some before actually attempting the entire trunk.

You don't neccessarily have to mastik all collar/duct connections as long as the liner is taped to the collar and the insulation is pulled all the way up to the trunk line take off and the entire thing is properly zip tied with duct zip ties at the collar. You do need to at the very least foil tape or mastick the collars to the trunk line to prevent air leaks there, but not the duct to the collar, that's what I should've said the first time around.

Your ducts on the floor are a no no. They should be strapped up.

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Old 04-25-2012, 05:29 PM   #3
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feasability of replacing AC flex ducting by myself?


It's fairly easy to replace ductwork. You just need a good plan and get some books from ADC or NAIMA to see how ducts should be installed. Manual D is very good to do and it will help you design your ductwork accordingly to your equipment and the required cfm for your cooling needs. If you have alot of space in the attic and you can move in and out easily then go ahead! But if you feel you may have trouble and stuff then just hire a company but you tell them what to do so it can be done properly. The only thing suks is the cost is very high if you hire a company. So that is something you might want to keep in mind. (especially with 19 registers!) The pro's on this forum can help guide you on your ductwork. I changed almost 80% of my ductwork and it wasn't that hard at all. I even suggest if you can get some help from some friends or hire a local handy for the day will help install your ducts even faster! It won't be the actual work that will take that long but it will be the planning part. good luck
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Old 04-25-2012, 05:35 PM   #4
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feasability of replacing AC flex ducting by myself?


Ask any hvac technician on here or any other forum or in real life, the minute a home owner "tells" us what to do as if we don't know our own job and you're on your own, we're out of there.

Talking to us, informed with the recently studied knowledge that we as well have and have had for years, discussing a plan of action together is alright. That way you can tell from conversation who is on the same page.

Tell us how to do our job? Do we tell you how to do yours as if we know more than you in your field? No.

Just saying.
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Old 04-25-2012, 06:31 PM   #5
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feasability of replacing AC flex ducting by myself?


Quote:
Originally Posted by Doc Holliday View Post
Ask any hvac technician on here or any other forum or in real life, the minute a home owner "tells" us what to do as if we don't know our own job and you're on your own, we're out of there.

Talking to us, informed with the recently studied knowledge that we as well have and have had for years, discussing a plan of action together is alright. That way you can tell from conversation who is on the same page.

Tell us how to do our job? Do we tell you how to do yours as if we know more than you in your field? No.

Just saying.
Sorry , I worded that wrong. Yes your right , we should do our research and see if the contractor knows what they are talking about when making a bid for the job.
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Old 04-25-2012, 07:01 PM   #6
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feasability of replacing AC flex ducting by myself?


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Originally Posted by Doc Holliday View Post
I'm not certain ow physically fit you are. Just off the top of my head I've never seen anyone over maybe 200 pounds work an attic and even then they only do the equipment, not the ducts. One slip and you'll be on the living room floor not to mention if you become too hot and you can't get out in time, say you're in a tiny crevice on the back of the home and away from the staircase, and you're all alone and have a heat stroke up there than that's it, game over. You don't have to be thin or fat to have a heat stroke, many people have 'em in attics.

Infortunately, and please don't take this the wrong way, attic work is a thin and hopefully athletic man's game.

Your metal trunk line is insulated internally, why it's not sweating.

Duct board is very easy to work with but you may need to practice on some before actually attempting the entire trunk.

You don't neccessarily have to mastik all collar/duct connections as long as the liner is taped to the collar and the insulation is pulled all the way up to the trunk line take off and the entire thing is properly zip tied with duct zip ties at the collar. You do need to at the very least foil tape or mastick the collars to the trunk line to prevent air leaks there, but not the duct to the collar, that's what I should've said the first time around.

Your ducts on the floor are a no no. They should be strapped up.
lol, as bad as this sounds, the attic is actually only 5-10 degrees hotter then the conditioned space i estimate, and were talking at about 2pm cst. the leaks i spoke of are pretty bad i dont know if i got that across. i dont think ill get anywhere near hyperthermic while up there untill the leaks are fixed.
for what its worth, while i would never consider myself fit, im not some sort of asthmatic or diabetic or some kind of scooter bound fat guy.
i am worried about the smaller spaces tho, but there is really only one, and that's the stretch of attic that has the main duct, the roof is sloping down toward the edge at that point and is pretty low. i was hoping to just cut several access holes where necessary, in the drywall in between studs so i can get stuff;and get at stuff, in the attic space.

if i were to replace all the ducting or atleast a good chunk of it, my goal would be to get it in such a condition that when i do actually replace the AC unit(within 5 years probably), id like to have done the job correctly, such that i could have it installed with this proposed ducting. is that reasonable? should i perhaps step up the quality of the materials i use in anticipation of maby installing a much higher efficiency unit later?(currently an 8 seer 4 ton i believe)
anyway ill reserve anymore questions untill i really dig into those manuals.

kilosos2, its actually 13, including the tiny ones in the guest bathroom and laundry room. idk where i got 19.

thanks for taking the time to reply, i really appreciate it.

edit: grammar

Last edited by Queequeg152; 04-25-2012 at 07:04 PM.
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Old 04-25-2012, 09:42 PM   #7
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feasability of replacing AC flex ducting by myself?


I wasn't trying to be rude, you asked and so I told you what I thought.

It gets well over 130f in the attics I'm in. In the middle of the day I can only go in for about 30 seconds and I have to come out and rest for 10 minutes, go back up for 30 seconds, come back down and cool off for 10 minutes and so on and so forth.

If you think you can do it than go for it. It's really not all that difficult. Once the science (manual j and d) is done with the labor can be leisurely seeing as how you don't absolutely have to do it all in one day as we would if you hired us. You can do one or two duct runs a day until the job is finished or however you want to tackle it.

For now you may want to simply concentrate on the existing metal trunk line, sealing it all up with aluminum tape and/or mastik (all the collars which are connected to the trunk line as well) and then only run new flex ducts. That is if the trunk line is repairable, not squashed and torn or flattened, and is simply leaking air at the seams which can easily be repaired.
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Old 04-25-2012, 09:47 PM   #8
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feasability of replacing AC flex ducting by myself?


Your sheet metal duct is lined duct. Which means its insulated on the inside.

Duck board, is best when cut on a duct board machine. There are hand cutters for it, but the set isn't cheap.
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Old 04-25-2012, 10:47 PM   #9
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feasability of replacing AC flex ducting by myself?


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I wasn't trying to be rude, you asked and so I told you what I thought.

It gets well over 130f in the attics I'm in. In the middle of the day I can only go in for about 30 seconds and I have to come out and rest for 10 minutes, go back up for 30 seconds, come back down and cool off for 10 minutes and so on and so forth.

If you think you can do it than go for it. It's really not all that difficult. Once the science (manual j and d) is done with the labor can be leisurely seeing as how you don't absolutely have to do it all in one day as we would if you hired us. You can do one or two duct runs a day until the job is finished or however you want to tackle it.

For now you may want to simply concentrate on the existing metal trunk line, sealing it all up with aluminum tape and/or mastik (all the collars which are connected to the trunk line as well) and then only run new flex ducts. That is if the trunk line is repairable, not squashed and torn or flattened, and is simply leaking air at the seams which can easily be repaired.
oh i wasn't offended in the least lol, if i was sensitive about being fat i wouldnt of mentioned it.sorry i shoulda made that clear . i live in houston, so i suspect those temperatures are shared here as well... all the more to motivation to do it now and not in June-august.

on another note, im looking at the ACCA store for the MANUAL J and D, and i see that they are 300+ pages? i thought i was getting some sort of booklet with charts graphs spreadsheets etc for calculating duct sizes, not a 300 page book. am i missing something?
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Old 04-25-2012, 10:50 PM   #10
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feasability of replacing AC flex ducting by myself?


Coincidence? I live in Alief, Bellaire and Kirkwood, southwest Houston. Been doing a/c here for 12 years. It's Houston attics I was talking about.
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Old 04-25-2012, 11:00 PM   #11
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feasability of replacing AC flex ducting by myself?


A Manual J is going to take into consideration the geographic location of your home (Houston), which way the windows face and for how long, if they're single or double pane, how many, insulation value, awnings and trees, etc.

You may not like what you find meaning you may be needing to change out the entire system and duct work.

You can purchase the software online and do it with a computer. There's also a few local companies that do it for a price.

Cool Science is one of them. Can't tell you the price, though, but they are supposedly highly experienced at this, heat load analysis aka Manual J, as it's all they do.
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Old 04-25-2012, 11:36 PM   #12
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feasability of replacing AC flex ducting by myself?


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A Manual J is going to take into consideration the geographic location of your home (Houston), which way the windows face and for how long, if they're single or double pane, how many, insulation value, awnings and trees, etc.

You may not like what you find meaning you may be needing to change out the entire system and duct work.

You can purchase the software online and do it with a computer. There's also a few local companies that do it for a price.

Cool Science is one of them. Can't tell you the price, though, but they are supposedly highly experienced at this, heat load analysis aka Manual J, as it's all they do.
i see, i wasnt sure if i was looking at a course textbook or something. am i right in assuming i can safetly go with the manual J-8 abridged version? my home is quite common , none of the out of the ordinary elements listed on the acca store.

i did see a few sites that sold the software, but tbh im looking forward to the challenge of doing it by hand. i do alot of cad work at my job so i suppose ill copy this houses bluelines into vanilla cad so i can get the lengths of duct etc necessary when doing the manual D. hopefully i dont find anything i didnt want to lol...

i actually live in sugarland, around 59 and 90. lol if i end up falling through the ceiling or something i may just have to give you a call.
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Old 04-26-2012, 12:01 AM   #13
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feasability of replacing AC flex ducting by myself?


Oh man, now you've gone and put me on the spot. I've never once performed a heat loss analysis so sorry, I can't help with the technical aspects. I only know what they consist of.

A few of these other guys have though so hopefully they'll jump in.
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Old 04-26-2012, 04:39 AM   #14
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feasability of replacing AC flex ducting by myself?


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Originally Posted by Queequeg152 View Post
i see, i wasnt sure if i was looking at a course textbook or something. am i right in assuming i can safetly go with the manual J-8 abridged version? my home is quite common , none of the out of the ordinary elements listed on the acca store.

i did see a few sites that sold the software, but tbh im looking forward to the challenge of doing it by hand. i do alot of cad work at my job so i suppose ill copy this houses bluelines into vanilla cad so i can get the lengths of duct etc necessary when doing the manual D. hopefully i dont find anything i didnt want to lol...

i actually live in sugarland, around 59 and 90. lol if i end up falling through the ceiling or something i may just have to give you a call.
ACCA has a spread sheet for MJ8 you can download, and also one for Manual D.

Its involved, but well worth it.
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Old 04-27-2012, 03:55 PM   #15
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feasability of replacing AC flex ducting by myself?


thanks beenthere, i wasnt aware of that spread sheet.
so the actual manual J and D books are strictly guides for filling out these spreadsheets? or are they more of a learning discourse explaining why things are done this way and not this way? my manual J wont be here till tuesday, cant wait to dig in.

i have another question somewhat unrelated to the OP. i was curious if there is someway i could quantify any improvement in air speed or even air leakage reduction?

i have an regular vane anemometer i use for measuring airspeed. as well as a static differential presure gauge for 0-2 inches of water. im thinking i could run the ac blower without the cooling off, and the registers blocked with tape and cardboard or someting... and just measure the static pressure inside the ac plenum with the pressure gauge before and after. id just measure the airspeed comeing out of each of the ducts with the anemometer obiviously.

i genuinely know nothing about hvac, is this idea hopelessly misguided? sounds too easy to be honest. ive seen how they use some soft of a fancy syncroness blower to pressurize entire houses to measure air leakage... but in this case id just be compairing before and after static pressures with the ducts blocked off.

thanks.

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