For splitting a main duct into two directions,awye would be less restrictive then a tee,to air flow.


But it sounds like you are refering to a branch duct ,off the main trunk.Not sure how a wye or tee fits that situation?

 

Hi.

It's not really splitting the main line into two (or is it... like I said I'm not an HVAC guy, just a nosy homeowner).

As I understand it there is a 10" rigid round duct feeding the upstairs zone. (It is installed in an engineered ibeam joist) and most of the registers are on one side of the house and I know he is splitting that line further down. But, there is one register closer to the furnace (with a 6" line to it), do you think the 10" duct would have a tee to the 6" line, or would a wye be used?

Just curious about how this is usually done, to make sure air actually goes to this register or doesn't steal all the velocity from the main line.

Yeah, I know.. but in my defense I am an engineer.. and I'm sure you know we get caught up in details and lose the real world perspective.

Matty

 

10" duct ,wyes to 6",what size is the part that continues on??

Duct designs and materials vary a lot by the region of the country,so I haven't seen this one.I have heard this(wyes) is common in Texas ,with flex duct .


Generally speaking a wye,properly sized,would yield less static(resistance to air flow)then a tee.Plus some possible labor savings.

What area are you located in?

 

It is the pressure build-up in the duct that disperses the air out into the individual heat runs. If the ducting is sized properly, once the trunkline is pressurized the air should flow somewhat equally through all the heat runs. Does that make sense?

 

doc hvac hit the nail on the head. Ask a engineer what static pressure is. Your system should be fine.

 

I think 10" continues, but I know it steps down later on in the run.

The explaination from doc havoc makes perfect sense, I was seeing distribution as more of a function of air velocity then static pressure.

Thanks folks for the explanation!

Matty

 

Actually I can't agree,static pressure difference moves air.

Many undersized sized can't move enough air to the runs farthest away from the fan,as the static is too low at that point in the duct system,due to the static losses of the fittings,etc., and undersized ducts.


For the OP,Manual D ,from ACCA,is what your contractor should have done to size the ducts,if he did ,I thnk he would gladly give you a copy.Manual D is not used by a lot of contractors,they use "rules of thumb".I hope yours used Manual D.

 

I know he did a Manual D analysis, we talked about it.

Basically, I was having trouble connecting with him in person about all this stuff and it was stickin' in my craw.

Thanks again for all your help!

Matty