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Old 06-30-2007, 04:43 PM  
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Default Ductwork

I am new to this, and am doing it myself so..! LOL I have 3 questions about my Ductwork, and there is a "layout", if you will, of the duct work description at the end of this!

First of all, I know my A/C or central unit is brand new and is working, but I think the duct work may/is laid out wrong.

I have sealed/caulked and insulated all of the ducts, (2) Y's and the plenum.

But, my daughter's room which is in the front of the house (North West side) is not getting enough cool air so I know it will be cold in there this winter. I have had to cover the West facing window in her room with foil just to try and help with the heat in the afternoons.

I have tried adjusting the air flow to all the vents but it is not helping.

The Front room measures (13' 6" X 8' 6"). There is a 6-inch duct to vent in the center of her room and is Y's off of an 8-inch duct (round). The other end of the Y is over my bed and is a 6-inch duct (My room is 17' 7" X 13' 11").

There are 7 other ducts in the house (full description is at the end of this message).

The two in the living room which runs parallel to the line that goes into the bedrooms. (To the East) An 8-inch duct that Y's off into 2 6-inch ducts.

The other 5 of them are 6-inch ducts that are direct from the plenum.

2 of the 5 are almost directly over the return to the unit. (Bad design I know!)

This is a rent house so I will not be "moving" the vents. But I was wondering:

1.) Should the duct work should be a different size?
2.) Should it be attached to the plenum differently? (I.E. should the 8 inch line not Y off into the Master, and just go down into a 6-inch directly to the Front bedroom)
3.) If the above question is correct will it be ok to Y off the 6-inch duct that goes into the back end of the Master Bedroom (closested to the plenum), and attach the 6-inch over my bed (which is roughly 15 feet from the plenum)?
3.) Should the 2 vents over the returns be 4-inch not 6? Would it really make that much differents?

The house is roughly 1500 square feet. And runs North to South, with the front door in the North End.

So the layout is (ruff measurements here! LOL):

1.) Front Bedroom (13' 11" X 8' 6") is on the North end 1 6-inch duct to vent, it is roughly 20 feet to the Y.

2.) Master Bedroom (17' 7" X 13' 11") South Western Side of the house 1 6-inch duct to vent on the North end, which Y's off from an 8-inch duct to the front Bedroom. It is roughly 15 feet to the plenum.
There is also 1 6-inch duct to vent that runs directly from the plenum about 5 feet into the South end of the Master front the door to the bedroom. The unit, and first return is located directly outside the Master Bedroom Door.

3.) Master Bath (7' 6" X 7' 6") is on the South Western side of the house. There is a 6-inch duct to vent directly from the plenum.

4.) Living room (21' 4" X 13' 7") is on the North Eastern side of the house and has two vents. The line to the living room runs parallel to the line that goes into the bedrooms. It is a direct line from the plenum and is an 8-inch duct that Y's off into 2 6-inch ducts.

5.) The Hallway (middle-southern end of the house) vent is about 2 feet from the unit/return and is 6-inch directly from the plenum.

6.) The Kitchen vent is in the middle of the Kitchen (South Eastern end side of the house). It is a 6-inch duct to vent and is also direct from the Plenum.

7.) Last but not least Laundry Room South West side of the house has a 6-inch duct to vent which is also direct from the plenum.

So there you go! LOL Hope that helps and is not TOO confusing! LOL

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Old 07-01-2007, 09:03 AM  
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A 6" diameter run will give out approx 100 cfm, which should be quite satisfactory for most rooms with an area of 160-180 sq ft of floor space with normal 8' high ceilings. Obviously, the R factor of the insulation will also play a huge role in any heating/cooling effort.
The size of the heating /cooling unit has a lot to do with performance together with properly sized ductwork. What are the specs on your unit/
Also, Return air plays a huge part in any system, and if not enough of it the Supply will suffer.
Do you have a "return" in this "hard to cool" room? What size are the other Returns?
More detailed info is needed for any proper advice,such as; Btu output, a/c tonnage, furnace fan size, return air main to unit, supply air trunk size(plenum)
Usually a heat/cool unit and duct system is designed by using Manuals J and D in order to obtain the most efficient results, taking in all the various materials that were used in the homes construction. Location,orientation, window and door sizes,insulation ,etc, all play a role in determing proper sizes.

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Old 07-01-2007, 10:47 AM  
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Default Ductwork

Well I did not build the house, and I am not sure I can give you the info you want about the unit.

I know it is a Carrier furnace an A coil Central Heat and Air Dowel Fuel Unit.

The only info I have on the coil is that is says "Design Pressure" 300 and "Refrigerant" R-22.

The furnace says (the label is not printed very well but I think it says) "Output" 88,000 and "Input" 71,000.

I could not tell you about compressor.

I do know for a fact that the furnace and A coil where brand new and installed last October, so they are not even 1 year old.

The Plenum is roughly 24 inches X 24 inches square and from where it attaches to the coil is roughly 57 inches. (I have insulated it so it is hard to go back and get exact numbers there). I know that when I was measuring for the insulation it was 77 inches from the top of the plenum to the top of the furnace, if that helps!

It is a vertical unit that sets inside a "closet" here in the hallway.

There are 2 (that are exactly the same) returns on floor level in the wall that are 19 inches X 16 inches Tall. The gap between the to (or from where I can take this one off and "crawl" to the other one is) it is roughly 45 inches long X 24 inches wide on the inside X 21 inches from the bottom of the filter to the floor.

It is not sealed off in this area either. Other then the insulation that I stuffed down in the wall to secure around the plenum and coils it can suck air from the attic. They did not seal it off any anyway.

When I was stuffing the insulation down there is about a 15 inch gap in the back of the plenum all the way down to the base/board that the plenum is setting on. But the right side of the plenum (standing behind it) is open all the way down to the floor/crawl space between the 2 return covers.

So I would think that it is getting more then enough air to suck back up and blow out! LOL

As for insulation, I know the insulation I bought to put in was at least an R-13. It is 3 1/2 inches think and is completely enclosed on a plastic moister protection bag (other then where I cut to the right size piece from the roll).

The new duck I got to replace the old one the receipt from Lowe's says "Silver Ins. Duct R4" it is a silver what I call "aero space material". LOL It looks like the shine silver duct work you see in the movies and NASA clips. That is why I call it that! LOL

I sealed/caulked everything and used "1.89" X YD UL Listed Duct Tape" and clamps both ends of the duct (where it attaches).

I Duct Taped the duct, then Duct Taped the insulation, then clamped over that making sure I felt to it first and had the clamp over the duct and not just the insulation part of the duct. So I know it is well sealed.

Then I also wrapped another piece of insulation around the (what ever it is called) part that the duct attaches to and goes into the ceiling. I sealed/caulked that as well.

I also sealed/caulked the plenum, and the duct branches that are attached to the plenum, and then insulated everything very well.

I know I probably went over board with the sealing/caulking and the insulation! LOL BUT I can guarantee you that there is NO air leakage and EVERYTHING that can be insulated has been!

I did not run another layer of insulation over the new duct work though. Its insulation looked exactly like the insulation that I bought so I thought it was good and thick enough to begin with.

That is the only other thing that I could possible insulate.

My ceilings are 8 foot high and the only vent that is in any room is the vent that the ductwork is attached too for heating and cooling the house. There are ceiling fans in eve room, except the bath and laundry room.

You have lost me with the "100 cfm" for an 8 inch duct. LOL That is over my head I just know that that room does not heat and cool the same as the rest of the house! LOL

Sorry I can't give you exact numbers on the unit! I am just a single mom trying my best to understand this and fix the problem! LOL

Thank you for your time and help!!
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Old 07-01-2007, 12:00 PM  
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The furnace says (the label is not printed very well but I think it says) "Output" 88,000 and "Input" 71,000.
************************************************** ******
It is an input of 88000 and an output of 71000 (80% efficient)

You have lost me with the "100 cfm" for an 8 inch duct. LOL That is over my head I just know that that room does not heat and cool the same as the rest of the house! LOL
************************************************** ********
a 6" diam pipe run will give approx 100 cfm.(Cubic feet per minute.) (this is normal)
************************************************** ***
It would be best if you have an air "balance" done on your system by an hvac pro. This method entails "'tuning" of the air supply into various rooms. It is done by dampering certain supply runs in order to give any weaker rooms more air. It should be done with air measuring instruments ONLY for obtaining best results. Also have your blower SPEED checked out. The return air from these weak rooms may be inadequate,have them checked out too.
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Old 07-01-2007, 12:47 PM  
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Ok! Well thank you for your help!

I will go to Lowe's and get some more 6 inch duck to run her own line.

The company that installed the unit for my landlord sent 2 different guys (1 came twice) to check the unit. One adjusted the ducts, and said he did not know what to do after that other then redo all of the duct work, and he added 1 1/2 lbs. of Freon to it. (So that is a total of 4 1/2 Lbs. in 9 months! But they say there is no leak so...)

The unit still was not working and was spiking from 75 up to 80-84 and running for 2-3 or more hours before bringing it back down to 75 and could not get it lower then that! Which it was doing BEFORE the 1st guy came.

Then the 2nd guy came and the blamed it on the duct work and some "flappy valve" thing outside in the Freon line (or the pipe next to it) not slamming shut all the way.

After another week (now going on 3 weeks with 80 degree days in and outside of my home) I decided to go up in the attic and look. I know the duct work worked with the old unit so I wondered why it was not working now!

Well when they took off the plenum they just stuck stuff back on! There where gaps that where not caulked, no insulation on the top half of the plenum, the duct branches where not insulated either. There is what I am assuming is supposed to be a whole for a vent pip out of the top of the plenum, which the just covered with a piece of card board and plain duck tape (not Duct Tape), as well as, 2 cigarette butts!! One of which was right on top of the plenum! LOL I thought all the ones I had to pick up outside was bad, but then realizing that they where smoking up there and put one out on the plywood and the other on the plenum itself just put it over the top for me!! LOL

Talk about BAD work! So after two more day and taking pictures and showing my landlord I went to Lowe's and got the stuff to just fix it myself!

The following week later (now 1 month of it not working right!), when they called to come and tell me they where coming to do the duct work I told them it had already been done and that was not the problem! (MAN do I wish I could have seen the look of there faces!! LOL I know they where screwing my landlord and I and stringing us along! LOL Sorry but this is the short and sweet story!)

I then told the owners daughter the whole store and with in 2 day they had worker #2 down here again going over everything (but the duct work which he did not even look at!) with me, and rewired the "flappy valve" to give it more juice to make sure it slams completely close.

It has been working every since, but I hope what ever he rewired does not mess with the heater this winter! LOL

So anyway that is my story! And how I became a duct working girl! LOL

Thanks again for your help! I just needed some where I could make sure that I did not need to change any other sizing of other ducts!
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Old 07-02-2007, 10:26 AM  
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Congrats on your personal troubleshooting that which the "pros" were unable (too lazy) to figure out.

Sounds like they simply left lots of gaps in the ductwork when they replaced the furnace and therefore you were loosing air to your attic.

Now you're LOTS more familiar with how your system works and should you run into trouble in the future, you're better equipped to understand what's happening. Sorry you had to learn it because of someone else's shoddy work.

The cigarette butts in your attic are just plain BAD business practice. The company should have policies that prohibit employees from smoking in customers homes unless the people living there give the express OK. And then IF they are allowed to smoke, they need to not leave their mess laying around.
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Old 07-02-2007, 11:04 PM  
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Default Ductwork

Oh it was SOOOO BAD work! LOL And this is just the short story! LOL

I told the company owner about the butts, and all of the ones I had to pick up outside!! She tried to tell me that they could have been up there until I told her that I knew they had to take the plenum off to put the A coil in and one was right on top! LOL

Anyway, Yes I know my system pretty well how and I have it working MUCH better! LOL

We will see what this winter brings and how much better it heats! Or if the "rewiring" that the last guy did messed the heater up! LOL

Thanks for everyones help! I think I have got it now!

And I am off to finish fixing the dryer duct that was 3 inch PVC pipe instead of 4 inch! LOL

And to see if I can figure out it anything is wrong with the pipes! There is a funky smell coming from some where and it gets worse with any rain! I also have it if I don't run the front shower every few day, which I know can be caused from the trap drying out. But I did not think it should dry out enough to smell in less then 7 days.

But I got spray caulk so what ever it is should get sealed off, and I will spray bleach on any water stains or mold I see.

Not sure those two are good ideas but it is all I know to do! LOL

Man my 6 year old daughter is going to know how to do all kinds of things! LOL Guess that is a plus for having a single mama! LOL
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Old 09-10-2007, 11:06 AM  
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Hello TXGirl:

Sorry, I haven't been on the Forum for a while; its obvious that you have some real problems.

1. I would bet money that the ducts are all flex duct. Air has an extremely hard time getting through flex duct. When it first came on the market the manufacturer said not to run it more than 3' because the efficiency drops off so fast.
2. Your ducts come off the plenum in the attic like a spider with really long legs. There should have been a rectangular duct run near the center of the house and measuring about 2/3 of the length of the house. Then, using proper 'take-offs' there should have been smooth, sheet metal pipe run from the retangular duct to the registers. Then all the duct should have been insulated. Rooms measuring up to 10' X 12' should have one 6" pipe and larger rooms should have two 6" runs. The living room needs three 6" runs; one of them being very near the door and the others over the windows. If we can put the air over the heat/cool loosers and keep up with them, the rest of the house will be fine.
3. I don't see you mentioning any return air ducts in any room. The rooms should have the door open or at least 1-1/2" clearance from the floor to the door which will allow free air return.
4. If the A/C system is not leaking any refrigerant, there should not be any refrigerant gasses added to the system. As much as your system has, you can go out to the condenser unit and find frost on the larger line because there is too much gas comming back to the compressor; a bad situation. The compressor can't continue to pump liquid refrigerant (unless it is a Copeland Scroll compressor). The refrigerant gasses don't wear out, they can only leak out. You don't burn up the gas in a cooling system, as you do in your car, it just keeps going from liquid to gas to absorb the heat, pumped to a high pressure, travel through the condenser coil to give off the heat and turn back to a liquid to be sent back to the 'metering device' at the evaporator coil. Then do it all again.
5. I admire your tenacity and your deductive reasoning. You are very smart.
If you need any further help, please post back and let us know.


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