Thread: How many supply vent and registers?

Hello everyone just wanted some input on minimum reqiurements for supply vents and registers (central Air), I did some research but I would like some input from the seasoned vets here on the messege board. What would you recommend as acceptable set up? What is the widley accepted standard?

Thanks in advance for your responses!

ROD

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If it cools the room(s), it's working (as far as supply and return air are concerned).

I would not attempt to get into the design of the system other than if the system simply did not cool (or heat) properly.

I've been in some houses where that was a problem, from day one, and it needed to be addressed by someone a whole lot smarter than me to solve the problem with a new duct system design and replacement of the duct systems.

On some other homes, especially on ones in one neighborhood in Hollywood, the building installed the AHU in a first floor closet, pumped the air up to the attic above the second floor, and expected the unit to be able to push that heavier cool air that high and then be able to still push that heavier cool air out to the supply registers. Did not work. Not on any of the several dozen homes I inspected in that neighborhood over 16 years.

The only correct was to move the AHU to the second floor and redesign the duct systems. After that was done, the systems worked properly.

The balancing of the system is outside of the scope of the inspection.

I force the fan on and leave it on during the interior inspection. I check each register/return for flow and comment on no or low flow. If there is not a cold air return in an enclosed foor (except baths) I comment on that and recommend that they at least leave a 3/4" gap from the bottom of the door to the floor covering for air transfer.

Thank you gentleman for your replies, I appreciate the assistance.

ROD

The proper method of setting up a residential HVAC system requires the contractor to do a load calculation using ACCA Manual J, select the system using Manual S, design the ducts using Manual D, select the registers using Manual T.

The minority of homes are designed in this manner. The majority are done using the "that's probably about right, it worked pretty well on a house that was kinda like this one" method. And then the installation guys use the "we don't have a duct that big on the truck, this will probably work almost as well" method. The result is the "Gee, my house is not as comfortable as my neighbor's and my system is bigger" syndrome.

There is a place for someone to do the calcs the right way and help the homeowner get it right but it's not home inspectors.

Originally Posted by Ron Dawes

The proper method of setting up a residential HVAC system requires the contractor to do a load calculation using ACCA Manual J, select the system using Manual S, design the ducts using Manual D, select the registers using Manual T.

In my experience it's Manuels that do the designing. That would be Juan, Santiago, Doroteo, and Toraidio . . .

Aaron

My take is taking into consideration the size of the unit vs. the size of the home, Then you would have to have a heat source for each room. If your temp differentials are between 14-22 between supply and register you should be fine. Any comments? (i'm new)

Originally Posted by Ron Dawes

The proper method of setting up a residential HVAC system requires the contractor to do a load calculation using ACCA Manual J, select the system using Manual S, design the ducts using Manual D, select the registers using Manual T.

The minority of homes are designed in this manner. The majority are done using the "that's probably about right, it worked pretty well on a house that was kinda like this one" method. And then the installation guys use the "we don't have a duct that big on the truck, this will probably work almost as well" method. The result is the "Gee, my house is not as comfortable as my neighbor's and my system is bigger" syndrome.

There is a place for someone to do the calcs the right way and help the homeowner get it right but it's not home inspectors.

Tom,

Ron's post is the correct way.

Originally Posted by Billy Stephens

Tom,

Ron's post is the correct way.

I Can respect that, however aside from the load calculations being outside the scope of the inspection process, are you saying that what I am saying does not hold any validity? My SOP asks for things like is there a heat source present in every room and are the temperature differentials within the acceptable range and the size of the unit. Maybe I was wrong in stating my asumption and do not , at all, intend on being misleading.
This business is way more complicated than I ever imagined but I am in for the long haul. I look to all of you for your years of wisdom and knowledge in the field and appreciate all your feedback( Even if I feel like an idiot)

Originally Posted by Tom Munds

My take is taking into consideration the size of the unit vs. the size of the home, Then you would have to have a heat source for each room. If your temp differentials are between 14-22 between supply and register

Each system is different and heat rise should be on the label.

Originally Posted by Tom Munds

I Can respect that, however aside from the load calculations being outside the scope of the inspection process, are you saying that what I am saying does not hold any validity? My SOP asks for things like is there a heat source present in every room and are the temperature differentials within the acceptable range.
This business is way more complicated than I ever imagined but

If you follow your SOP and system is out of range call in HVAC.

Don't sweat the National Exam review the material before hand and don't do a lot of double guessing yourself you'll do fine.