Duct Branching

[Steve Wiggins]

I mostly agree with Dash.

P. Student has some great points but they are in a perfect dream world. Nice goals to work toward though - keep going p.

One of my pet peeves is connecting the flexible duct straight to the boot box. When I walk through a new construction house I want to see clean shiney metal inside the box with a nice clean metal elbow making the turn.

The only place flex is ok (and in some cases preferrable) is between this metal elbow and a metal wye (or elblow and metal starting collar @ plenum.

My preference until someone talks me out of it:
1. Well sealed, easily accessable air filtering system

2. Metal plenums, screwed and sealed with clear silicone (or mastic)

3. Externally insulated metal boot boxes with metal elbows on them. Usually 3 way throw ceiling mounted on an interior wall with curved blade grille (not stamped face).

4. Flexible duct supported in the attic slightly up off the blown insulation. Ran in a way to provice the smoothest possible air flow path. Yes round metal is better but not practicle in the places we are asked to install it. And round metal is better than rectangluar metal, esp when the rect. in insulated on the inside.

5. No dampers. They are for inadequate duct designers and only hamper air flow.

6. Accurate thermostat location (usually close to return air intake) but definately NOT where supply air will blow on it. If two story home need one on each floor. Not in line with sunlight beam through windows. Not inline with fireplace radient heat. One or two extra conductors just in case. Digital but NOT programmable. Top plate wire penetration and wall hole SEALED air tight.

7. Outdoor unit secured level on its own poured concreted pad attached to the house so it won't tilt later. Mounted at least 10" to 12" away from the house so it can be washed on the backside.

8. TXVs & start kits are essential among numerous other safety features. I prefer recips over scrolls but that is purely opinion mostly due to noise and breakdown problems.

9. Crankcase heaters = longer compressor life no question. Most all equipment has been stripped of these features (#8 above also) to the detrement of equipment life and the benefit of manufacturers saving on cost.

10. Indoor cooling coils ARI match in new construction. Inspectors only look for that yellow energy tag on the outdoor unit to verify SEER rating. They have no clue of the indoor sections abilites or ratings. This is really sad for the home owner. Lifetime warranties can be denied because of this mismatch.

CONCLUSION:
There are SOOO many things a good inspection should reveal to the homeowner but 99% are mised by non professionals. This is a battle between TREC and the TDLR/TACCA in Texas. I think there is a need for these inspections but not by unqualified people. An inspector stating some problems and then saying the system should be checked by a professional only causes problems and doesn't help them. With some work in Austin I think inspectors and professionals can strike some sort of truce to help increase public trust.



[Edited by Steve Wiggins on 01-09-2005 at 02:31 PM]

[tinner73]

no dampers?? how do you regulate (direct) the airflow? whenever you put in a tee of any kind the should automatically be a damper installed.

recip over scroll?




i dunno about those Steve.

[trane]

Air will always take the path of least resistance. I don't know how you can get by without dampers. We put dampers in the main ducts anytime there is another duct going off from it and dampers in all supplies.

[Steve Wiggins]

Originally posted by tinner73
no dampers?? how do you regulate (direct) the airflow? whenever you put in a tee of any kind the should automatically be a damper installed.

The only tee I would see is the supply plenum. If your plenum is the right size (not those supplied by the manuf) and the holes are cut in the right locations you can get pretty close to predicting the air flow from each run. Since heat load are variable and duct sizes are not there is no way to be exact. If heat loads were constant and air flow to each duct was variable then yes I would agree with dampers.

Dampers (for balancing purposes) are an engineers crutch and should only be used when the symptoms call for it. All the residential dampers I have seen are left wide open anyway so why bother and hamper air flow?

[pjsullivan]

Steve:

What sorts of problems do you encounter with home inspectors? I'm sincerely interested in finding out.

My inspection of HVAC systems includes the following:
a. Check temp drop (14-22 deg).
b. Check temp rise (if manufacturer's specs available).
c. Look for visible damage to unit or heat exchanger.
d. Check for gas leaks.
e. Flame is correct color, size, and burns properly.
f. Blower is clean, and runs smooth.
g. Flue is secure, and has proper clearance.
h. Condensates are properly configured & insulated.
i. Pan is in good shape, and pan switch works.
j. Proper work space in front of unit & accessible.
k. 110V outlet & emergency switch are available.
l. Electrical wiring is secure and not a hazard.
m. Check for air leaks around plenums, and connections.
n. Check filters for correct size, and cleanliness.
o. Outdoor condenser is level, and runs smooth.
p. Suction line is well insulated and secured.
q. Shutoff panel is accessible, and properly wired.
r. Circuit breaker in main panel is correct size.
s. Size of supply wire is correct for installed breaker.
t. Look for visible damage to condenser (fins & fan).
u. Operate thermostats in heat, cool, and manual fan.
v. Location of thermostat is near return, not in direct sun, and not near supply duct.
w. And other stuff I'm probably forgetting right now.

I do home warranty inspections (1 year home whose builder's warranty is about to expire), and the #1 complaint is the HVAC system not delivering enough hot or cool air to various parts of the home. This type of thing is a really pervasive issue throughout the new home industry. Even custom homes use flex duct strewn all over the place. I inspect 300+ homes a year, and I have only once seen rigid metal duct in a new home. Is this just regional (Texas?), or is the problem a matter of builders not wanting to spend the extra money on a quality designed and installed HVAC system? I think you mentioned earlier that most spec homes do not have a system designed for the home, and I agree. I'll inspect a specific model of a spec home, and it'll have a 3.5 ton unit downstairs with a 2.5 ton unit upstairs ... the following week, I'll inspect the exact same layout two blocks away with a 2.5 ton unit down, and a 3 ton up. What's up with that? What's more, it's the same HVAC company doing the work!

You indicated problems between TREC & the TDLR/TACCA in Texas. What sort of solution would you offer to help mend the relationship in order to regain the public trust?

I understand the need for more qualified people in the inspection indusrty, but when we are faced with the abominations that pass for HVAC system ductwork of the like I've illustrated in brand new homes ... what qualifications do we need? All of the pros in this forum seem to agree that improperly designed systems are the root of most poorly operating HVAC systems. So why don't the systems get properly designed?

BTW, as of 01/2005 TREC now requires a professional inspector applicant to have 448 credit hours of approved coursework (it used to be 188).

It seems that whenever an inspector raises a flag, he gets shot down because he's not qualified to raise the flag. Fair enough, but if we can all agree that the systems being installed in new homes are basically crap, then what's wrong with raising a flag now and then? Just maybe if the builders have to call back the HVAC installers often enough, then things will get better over time (I'm propbably being overly optimistic).

Steve, you are preaching to the choir. I abhor using the phrase "Recommend a qualified HVAC professional evaluate ... etc". I wish I was more qualified to make sure that I was not wasting a HVAC pro's time ... but I have to know about foundations, grading, roofs, attics, structures, doors, windows, water heaters, plumbing, electrical systems of all ages, and all kinds of other stuff as well. There's just not enough time to learn everything.

Anyway, I'm rambling.

Peter.

[dash]

Originally posted by tinner73
dash...my arch nemesis...please tell me why an all flex system would be better than an all metal one.

Didn't say it would be better,just that properly designed,there is no air flow difference between the two.

Metal is more difficult to seal and insulate,and is seldom done correctly in Florida.I've never installed metal in my own homes or business(have in many others,in the 60's and early 70's).I don't see the value of the increased cost.

Of course Florida is all most exculsively ductboard and flex.

[davidr]

Originally posted by Steve Wiggins

Dampers (for balancing purposes) are an engineers crutch and should only be used when the symptoms call for it. All the residential dampers I have seen are left wide open anyway so why bother and hamper air flow? [/B]

Steve,I have to disagree with you on this one.
Dampers are there because no design process is 100%.
Things change in the field that don't allow the duct to be installed in the exact way the designer intended.
There are too many variables that can take place which will affect air distribution for them not to be installed.
If an adjustment needs to be made on start up to allow for airflow adjustment it is nice to have them there.

[pstu]

I just wish there were a way to get the real problem in your crosshairs -- absence of competent HVAC design. Kudos to you PJ, if you ever get a legit reason to nail those builders who make a mess of our HVAC systems!

-- P.Student

[Steve Wiggins]

Originally posted by pjsullivan
Steve:

What sorts of problems do you encounter with home inspectors? I'm sincerely interested in finding out.

Home seller calls me and says the "home inspector" left a report that says the "coils are dirty" and the system needs to be "serivced".

This happened to me recently and here is an example of how the call went:

I asked the home seller which coil the inspector was talking about (indoor or out). She didn't know and the inspectors report didn't specify. So I checked them both and both were very dirty as was the evap drain pan.
The indoor coil required removal to clean it and it had a non repairable refrigerant leak. Checked charge and system was low on refrigerant and the run cap was only half value µf so it ran the compressor but needed replacing.

When I told the seller of the problems she was very angry at me because she wasn't about to pay for all those repairs. She only wanted done what was on the inspectors report so she could sell the home. She didn't give a rip if the system worked correctly or not.

In her eyes the inspector was the ultimate authoritative professional and I was merely the grunt hired to "do what I was told".

The problem here lies with the wording the inspector used. The wrong word was "service". If the inspector had used the word, "evaluate" everything would have worked out.

Please please please all you home inspectors out there make sure you tell the customer to have their system "evaluated" NOT SERVICED by a licensed professional. Further state in writing that you are NOT a professional and that the licensed contractor is most likely to find things wrong above and beyond what was covered by your inspection. Systems cannot be serviced without evaluating them first.

The above example has happened to me more than once and I see a terrible problem developing in the state of Texas in this area. The end result was the HO was furious with me and refused to pay the bill. They will never call me again and am sure it will tarnish my reputation by them telling others. I did my job as politely and professionally as I could and still didn't gain public trust.

[Edited by Steve Wiggins on 01-09-2005 at 05:37 PM]

[Steve Wiggins]

Originally posted by davidr

Originally posted by Steve Wiggins

Dampers (for balancing purposes) are an engineers crutch and should only be used when the symptoms call for it. All the residential dampers I have seen are left wide open anyway so why bother and hamper air flow?

Steve,I have to disagree with you on this one.
Dampers are there because no design process is 100%.
Things change in the field that don't allow the duct to be installed in the exact way the designer intended.
There are too many variables that can take place which will affect air distribution for them not to be installed.
If an adjustment needs to be made on start up to allow for airflow adjustment it is nice to have them there.
[/B]

Changes in the field need to be reflected in the design and not corrected by a bandaid dampering system.

No one that I know ever checks cfm at each register to see if it matches the designed value. The only reason a damper would get adjusted is if a HO complained and then when the seasons change they are uncomfortable again. They just get tired of calling the contractor about it and put up with the discomfort. All the while the contractor is thinking he actually fixed the problem.

[Steve Wiggins]

Originally posted by pjsullivan

e. Flame is correct color, size, and burns properly.

Peter I am very worried about this statement.

1. What color are you looking for?

2. What size is the right size?

[Steve Wiggins]

Originally posted by pjsullivan

Size of supply wire is correct for installed breaker.

How do you determine this?

[davidr]

Originally posted by Steve Wiggins

No one that I know ever checks cfm at each register to see if it matches the designed value. [/B]

Well now you know at least one person,trust me there are others.
If we have a sizeable difference in how much CFM an area takes in heating & cooling we recommend zone controls.
If you take the time to adjust your systems there won't be as many unhappy HO's.
It is not about making the system perfect,this is not practical.
What it is about is making your customers comfortable & making sure they are getting what they paid for.
With that much confidence in your duct system design you should appreciate having it tested to verify your design has been achieved.
All it would do is give more credibility to your engineering skills.

[davidr]

Originally posted by Steve Wiggins

Originally posted by pjsullivan

e. Flame is correct color, size, and burns properly.

Peter I am very worried about this statement.

1. What color are you looking for?

2. What size is the right size?

Steve I agree with you 100%.
The only way to be sure an appliance is burning properly & safely is through combustion analysis.

[tinner73]

Originally posted by Steve Wiggins

Originally posted by davidr

Originally posted by Steve Wiggins

Dampers (for balancing purposes) are an engineers crutch and should only be used when the symptoms call for it. All the residential dampers I have seen are left wide open anyway so why bother and hamper air flow?

how would an open damper hamper the airflow.




Steve,I have to disagree with you on this one.
Dampers are there because no design process is 100%.
Things change in the field that don't allow the duct to be installed in the exact way the designer intended.
There are too many variables that can take place which will affect air distribution for them not to be installed.
If an adjustment needs to be made on start up to allow for airflow adjustment it is nice to have them there.

Changes in the field need to be reflected in the design and not corrected by a bandaid dampering system.



dampers are not band-aids they are valves. how else do you control the volume? how do you control the flow of water? with a valve (damper).



No one that I know ever checks cfm at each register to see if it matches the designed value. The only reason a damper would get adjusted is if a HO complained and then when the seasons change they are uncomfortable again. They just get tired of calling the contractor about it and put up with the discomfort. All the while the contractor is thinking he actually fixed the problem. [/B]

..if the homeowner complained then a damper would be the ONLY way to re-direct the airflow. dampers are cheap and as long you don't bury them under drywall, they should ALWAYS be installed.

[caliweath33]

I can't believe that PJ Sullivan is now trying to blame immigrant workers for this crappy duct design. First let me tell you that behind that desk designing these systems is an old us of a good old boy.I can guarantee you that the only language good old boy speaks is english and nothing else. Also parts lists are supplied from you guessed it the good old boy from behind the desk. The only difference you would have if you replaced the so called immigrant workers with 100% us of a good old boys would be very high employee benefits, sh##load of workers comp. Backed up on builders schedule and so on and so forth. You need a new job if all you do is use hard working people as scapegoats everytime you have to use your brain.

[41gasman]

pjsullivan. I commend you on your efforts to do a indepth
inspection for your customers.This is very rare around here.
I have been in a nasty little crawl of a home a week after there closing to install gas pipe(hard pipe of course).Only
to roll over and soak my shoulder in what was not quite
just water. The 4" sewer main was leaking and there was
a big white ring were the "water"had flooded and evaperated.
How this was missed I don't know.I know of one home inpector
around here who try's this hard.And sellers don'tlike him.
But buyers love him.I have seen him cause people to get
quite irritated. Because he really "inspects" a home.
It seems to me the way for you to really check a hvac
system would be to do what you all ready do.Than use the
hvac-cal that is sold here.That and a air flow hood would
very quickly put the ball in the installer court.Let them
prove you wrong.You just got to know they went by a"rule of thumb".And that's before the installers whith very little skill,or thought to a job well done.And in a big hurry!
Around here installers get a way with murder because of
the mild weather.Back to back to back 6"dia. 90's going
into wall stacks two floors up!!And the customer wants to
know why the bedrooms up stairs are so cold all the time.
It's called "hack and slash"here.I do mostly retro fit's
And it can be a real bear to fix alot of this and make
a buck at the same time.I love my trade a lot.And find
some of this stuff very embarrassing.But I digress.Good
luck with you efforts. And keep up the good work!

[cem-bsee]

again, ACCA manualJ is used to determine the load, given many physical parameters & the designer makes certain assumptions. manual S is used to size the equipment | unit. manual D is to design ducts for airflow necessary for the equipment and the loads. [ perhaps a local commercial plumbing shop will let you come & see manualD, one here did]

Same info are in ASHRAE manuals [ ~$150 ea ], which have LOTS of design info; in 4 volumes, one updated ea year. [ Engr school libraries may have <1990 vintage, $$$ have prevented most from just getting them since then. In fact, none in a 400mi radius of me had one! including Purdue, GA Tech, ... ]

regarding the ductwork, good insite can be gained just viewing the 3-4 pages of manD relative to "equivalent lengths" for the various fittings; eg: wye, tee, scoop take offs, etc.

remember that air is a fluid which can be compressed.

Leakage is a BIG concern along with duct sizing and its insulation.

[Edited by cem-bsee on 01-09-2005 at 08:14 PM]

[fat bob]

Originally posted by tinner73
flex duct degrades the airflow. it is not smooth like the metal pipe. the smoother and squarer the duct, the better. the part here that gets me is even if you went with CHEAP round "stove" pipe it would be way better than this. it would be fairly close in price and you wouldn't need a
tin-shop. this way saves on labor mainly and what's more important than their bottom line anyway. i'm happy they don't do this around Chicago.

I've heard that Chicago still requires cast iron drain pipes--no PVC--and armored power lines in the attic. That's good for plumbers and electricians, and I suppose makes for a better house. But I wonder, are Chicago's codes looking out for the trades or the homeowners? Maybe both.

[tin_fab]

armored power lines in the attic

No BX or romex except for 3'BX whips..all EMT conduit
No pvc for DWV OR potable....cast iron and copper
NO FLEX SYSTEMS...5'of flex or less and sheet metal required

Yes Chicago protects homeowners and requires trades to know their stuff