Isn’t a “Y” better than a “T”?
With the help of an HVAC contractor I’m installing my own heat pump and ductwork. It’s a 2.5 ton split system. He brought me all of the materials (boots, ductwork, condensing unit, air handler, misc. supplies, etc.) and told me to begin by assembling, wrapping and installing the boots in the locations he designated. I did that.
I’m now supposed to install the air handler which will be located on a platform in a closet in the center of the house that is adjacent to a hallway (this is a ranch floor plan). A central return will be cut into the hallway wall beneath the air handler. The contractor has provided a tee (14″ round sheet metal) that will be positioned 24″ above the air handler and will direct the discharge air through the ceiling and down the trunk line in opposite directions.
I’m not an HVAC contractor, but I am a picky DIY’er and really want to do this right. I’m inclined to believe that a wye would handle the thrust much better than a tee and would also reduce turbulence. The contractor says that a tee will work just fine, but I’m hesitant to install it.
Am I wrong to be questioning his judgement on this?
New knowledge is priceless.
Used knowledge is even more valuable.
Replies
Technically, you're correct. Any change in the direction of flow in a piping or duct system adds resistance to the flow. An abrupt change in direction adds more resistance than a gradual change. That's why a long radius bend is better than a 90* elbow - and a wye fitting would be better than a tee.
You're HVAC guy is probably right, however, about the tee working just fine. You're dealing with pretty low velocities in a 14" duct, so the difference between a wye and a tee is probably negligable. Other possible issues might include cost of a wye v.s. tee, installation clearances, additional ducting, etc.
Assuming you get along well with him, just ask for an explanation. I know that I'm always willing to explain something to a customer who actually wants to understand.
I have to agree with Dave, the fitting used will have very little impact on the system. A wye would be ideal but probably tough to find and the system is designed to work off pressure anyway, not necessarily velocity (although that is used in the design). That is the reasoning behind avoiding a take-off in the end cap. I generally do square duct and put a splitter in the tee to help balance the system. But round pipe generally has better airflow, so no problem.
Thanks for the feedback, guys. My contractor said basically the same things you did. Unfortunately, we've now moved on to a different issue on which we disagree. He's provided me with a half-dozen rolls of Shurtape (just glorified duct tape in my humble opinion) to seal the joints of the sheet metal. It's not even labeled with the 181 listing. I'm insisting that mastic should be used on the sheet metal joints.
He says that he's been using duct tape (not foil tape) his entire career and has had no problems with it. He might be right. However, I try to educate myself thoroughly before starting these projects, and just about everything I've read implies that mastic is superior to tape when sealing sheet metal ductwork.
New knowledge is priceless.
Used knowledge is even more valuable.
Agreed. Mastic is better, actually provides a better seal easier. I have used some of the best tape and it still will eventually give it up, especially in your area. I have run miles of duct in South Carolina and mastic is almost always preferred. For tape to stick, the surface needs to be clean and I have not seen and galvanized metal without some oil or other material on it. Paint way. Just Google duct mastic and you will see the opinions....
Edited 6/8/2007 9:04 am ET by ErnieK
If you want to go with mastic, and your contractor friend won't budge, HD sells it, or did. Just wrap the joints with stick-on fiberglass drywall tape and paint the mastic on.
Of course he hasn't had any problems. He's not there years later when it falls off. Having said that we never ever sealed any of our ducts ( nor did any of our competitors) unless the ductwork was going through an un conditioned space. The theory (so I was told) was that any leakage of heat or cold was going into the same space that needed to be heated and cooled anyways and any leakage at the connections was minimal at best. Whether you think it is right or wrong I'm having difficulty remembering anyone ever using it. Though I have seen older house with duct tape (that rotted off) with no screws holding the pipes together all fallen apart inside ceilings.
roger
To correctly apply mastic, work it across the joint, forcing it to go into the joint and then smooth it out by working it in the direction of the joint. The objective is to have the mastic in the joint instead of on the surface. On the surface it is little better than tape. Keep up the good work.
Might depend upon the T, too.
Used to be, the ductwork bender would ask if the T needed a diagonal diverter in it. Kind of a pain to install, so it's just the sort of thing the sheetmetal people would remember but not be sad to see pass into history, either.
Now, my preference for that mechanical closet is to frame it as frame-within-frame to isolate some of the noise. I like building it entirely "inside" the closet footprint, too--that allows using standard door frames & trim (with a stock louvered door, too, skipping the less-pretty return grill altogether). The biggest headache I used to have was in making sure nobody "helped out" with floor drains or the like that are open to the return air plenum <sigh>.