Where to start ... improve leaking duct(s) right at air handler


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Old 05-11-14, 07:24 AM
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Where to start ... improve leaking duct(s) right at air handler

Hi, we purchased our current home back in November of 2013 and I've been in the "new house" mode ever since. It is exists here I'm attempting to improve it. The previous owners were a bit older and also had the responsibility of caring for one of their older parents. I think they were busy and/or just plain lazy and possibly didn't know how to turn a screw driver. As such I've moved from project to project. With summer coming I've turned my attention to the HVAC system.

The home is a 2 story with full basement brick home built in 1977. With the finished basement it is approximately 3000 sq feet. One of the first things I've noticed about the state of the HVAC system since moving from heating to cooling, besides its age (15 yo Trane AC / 23 year old gas fired furnace), is that the basement area where the system exists is FREEZING. This is a single system for the entire home so there is a lot of duct work going on. Complete with dampers, etc. A quick once over found some seams "patched" with duck tape (Alabama chrome or regular duck tape not foil duct tape). I also found several "peeker" holes cut to view the direction of the dampers. These were actually sufficiently taped with foil which leads me to believe at some point a professional did the cut, inspection and reseal.

As might be expected with a single system attempting to heat/cool a home of this size I've got considerable hot/cold zones. So I think the obvious down the road solution is likely either dual units or a possibly a larger one (I believe this one to be 3 ton).

However, in the meantime I'm looking for answers on at least improving the air flow/leakage/loss at the air handler. I think that at the least is to remove the duck tape and reseal those seams/joints with foil duct tape. Look for obvious signs of leaking joints and patch if possible. There are also several sections that are using transition pieces to accommodate short runs of odd angles that are using a flexible fabric like material. These appear to be extremely inefficient.

Any other things for a novice to look for here?

Pardon me if I used odd or incorrect language as I consider HVAC systems and the proper nomenclature to be among my weakest areas of knowledge regarding homes.

Thanks!
 
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Old 05-11-14, 08:07 PM
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First place to start is getting a small smoke generator such as a Wizard Stick. Amazon.com: Wizard Stick: Toys & Games You use this to find any leaks in the ductwork when the fan (blower) is running on manual.

I would remove ALL the cloth "duck" tape and then use mastic to seal the joints. No fan/blower running when sealing. Some people like to use a "belt and suspenders" approach and first use the foil tape and then cover the tape completely with the mastic.

Can you post some pictures of the "flexible fabric" material? Flexible joints are not uncommon in ductwork and depending on what material or where located may not be a problem. Both close up and from a distance are best and be sure they are well lit and in focus.

Several more things with the rest of the system but start with the ducts.
 
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Old 05-12-14, 05:04 AM
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Thanks Furd.

I've got the Wizard Stick on order and have already started removing the cloth duck tape. Ran out of foil tape, but will pick some more up this evening.

Is there a particular mastic that is preferred? I like the belt and suspenders approach.

-OpusX
 
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Old 05-12-14, 05:43 AM
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I'm at work so pics of the flexible duct interconnect will not be possible till later.

However, it looks a lot like this material here. I believe it to be a large part of my air loss as it is older and the corners look to be cracking.

ComfortGurus.com: DuroDyne MBX4-100 - Black ExcelonŽ Flexible Duct Connector (1 ft.)

 
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Old 05-12-14, 03:51 PM
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What you linked to is actually a very good flexible joint material. The problem comes from sealing the sheet metal to the ducts AND the rubber to itself. For the latter they use a proprietary cement that has a shelf life of only a few months in the bottle. Determine exactly where the leak is and I may be able to suggest something.
 
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Old 05-14-14, 05:55 PM
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Leakage seems unlikely to be the cause of your problems, most residential heating systems leak like sieves and work properly.

Your 3 ton unit should be adequate size barring any special circumstances to your particular house. Unless you have major heat gain due due certain exposures.

Questions:
1. Were the areas that are cold now hot in the heating season?
2. Are the dampers that you mentioned in the large trunk (square) duct or the smaller branch (4"-7" round) runs? If they are in the trunk duct are the interconnected so that one closes as the other one opens?
3. Are your supply registers on other floors closed off or blocked?
4. Do you have adequate return air in your basement? Often when basements get finished after initial construction people forget to add proper return air.
 
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Old 05-15-14, 06:10 AM
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While I don't believe leakage to be the root of my problems I do believe it is having an impact based on just how much air appears to be leaking in the area of the air handler. There is easily a 20 degree temp difference in the area of the air handler and everywhere else. After starting this thread and doing some basic research it seems that little to no work was ever done to seal up the mass of elbow joints, seams, etc in this system. As said before there is A LOT of duct in the general area of the air handler and hardly any is even taped let alone sealed with mastic.

This is a two story home with full basement. I just realized in my original post I said it was approximately 3000 sq WITH basement...that is incorrect. It is actually approximately 4000 sq ft WITH basement. Basement is 85% finished. Above grade sq ft is 2663.

Being a two story home and this our first warm period in the home, we moved in December 15, I am starting to see the inadequacies of the system cooling the second story.

Back to your questions...

1. Yes / No. Some areas appear to be well supplied while others, specifically areas of the second story, are not.

2. Dampers are all in branch runs.

3. Where applicable I have closed supply registers. Almost the entire first floor register are closed as it is well cooled/heated.

4. I would believe so. I have a large return, in the basement, with a short run of approximately 10 feet right to the air handler.
 
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Old 05-15-14, 06:15 AM
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At this point taping and applying mastic to all visible duct can't hurt right? At worse I'm out less than $50 and a few hours of my time this weekend.

I did receive the smoke generator yesterday so I plan on using it to help determine which dampers affect which supply branches, and to isolate leaks at the air handler its self.

Thanks Furd and Shylier. I look forward to hearing more back from you.
 
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Old 05-15-14, 08:17 AM
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Question similar question about sealing leaks and improving flex duct runs

I'm in a somewhat similar situation. We have poor airflow from registers in several rooms. After inspecting the ductwork in the attic, it looks like there are not only leaks (mostly minor) but flex duct that is crimped, pinched, sagging, goes up and down in the run, or is a very long runs (25+ feet). Some of the flex goes directly from plenum to outlet, but most of it is connected to hard pipe and then finishes at the outlet.

My plan is similar to opusX to seal the leaks; also plan to eliminate the crimps and sags on the various flex sections so the air has less obstacles.

This should improve the airflow in those ducts, but will it also impact the other supplys coming out of the plenum? In other words, will making those ducts more efficient screw with the pressure in the plenum or is that pressure more or less constant since I'm not changing the start collar sizes, or duct size or duct length?

(This is first time dealing with ductwork so hope that makes sense!)
 
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Old 05-16-14, 04:23 AM
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Sbenn,
Fixing sags and "crimps"(?) shouldn't affect your pressures much, a typical house is done using an extended plenum system which operates primarily on static pressure. That static pressure needs pretty major restrictions (like a bunch of registers closed off) to be affected. Inversely, you need some pretty major leaks to affect it going the other way. How bad are the sags in the flex joints, these could change pressure a bit if they are bad enough to change your net free area in a large duct (1/2" sag reduces your NFA by 1" times the width of the duct opposite the sag).

opusX,
No it certainly can't hurt to seal up your joints, if you are able to post a picture of the suspect leaks before you get them coated with mastic it would be helpful. The only place I typically use mastic is for exhaust/fume hoods in large blow pipe systems, (ie. Welding Exhaust) where you don't want to risk any contaminants escaping. For supply air in commercial install we use duct sealer, either with or without teflon additive. It is similair to mastic and I suspect you may be incorrectly referring to duct sealer as mastic. Mastic is a two-part system where you place a fabric tape over the joint and brush over a thin liquid, similar in process to drywall taping. Duct sealer is a thicker brush on sealer about the consistency of drywall mud or a little thinner depending on the brand and use. Residential we never use anything, if I don't screw the branch runs I'll use a piece of duct tape and that is about it. Residential is pretty forgiving.
Be careful shutting registers down too much. Your duct system is designed to move certain volumes based on the pipe diameters delivered to rooms. That said they often get designed poorly which causes those hot/cool spots. You are on the right track identifying which dampers go to which rooms. Once you have those identified try to balance each floor, not each room, from the dampers rather than the registers. Being a 2 story you are can try shutting down your main floor runs about 25% and your basement runs around the same for a starting point. Make sure all of your return air grills on all floors are clear (no couches in front) while doing this.
 
 

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