Return Air Vents

Garasaki

Essentially there is no such thing as an oversized return duct. You can have oversized supply (as there is a certain velocity you want the air to shoot out of the supply register at) but not really return.

2) Still would be a good idea to get a bigger plenum on there. Or at least one that's appropriately sized. Maybe your current one is, I don't recall. But remember all the air going back to your furnace has to flow thru there so it could be a major restriction

4) You'd be better off having 2 takeoffs rather then 1 takeoff then a Y. Amoungst other things, it'll probably be cheaper to have 2 takeoffs.

5) If you add balancing dampers (at about 3 bucks each...) into the ductwork you add, you will be able to balance the airflow so the vents you add near the furnace won't blow way more air then the ones that are far away.

stubits

Great info. Thanks!

I don't actually know the size of my plenum. I will check that out tonight. I do know that I use a 20x16 filter, and the plenum seems to fit right up to it, so I'd guess that's at least part of it.

I am actually suggesting 2, maybe three trunks coming out of the plenum, 1)the current 12x8 will suck from the second floor, 2) a 14x14x14 wye to pull from the main floor and perhaps 3) something to pull from the basement. Am I understanding you correctly?

I have balancing dampers on all the supply vents, are you suggesting balancing dampers on the return vents as well?

Thanks!

Garasaki

The plenum probably forms a lopsided "ell" with 20x16 being a bigger dimension (horizontally into the back of the furnace) then it likely necks down for the vertical component.

Again I'd suggest just bringing each new run as a separate takeoff from the plenum. Your calculations will probably tell you a 14" round duct can handle about 650 cfm. That same calculation applies to the Y too. Your planning on having 650 cfm thru each branch, so that means the "base" of the Y will have 1300 cfm. Way too much air for a 14" round duct. It will be an area of large restriction.

Typically in residential heating/cooling, you wouldn't see balancing dampers on the return. But you CAN put them there. And since your goal here is to even out the airflow thru your house, it seems like a logical step. Especially for the low initial investment. An installer would probably tell you to forgo them. Again, I'm saying for 15 bucks...why not? Could come in handy.

stubits

I'll check out the dimensions of my plenum tonight. I think that will help a lot in figuring out what to do here. Unfortunately the utility closest that houses the furnace, as well as my hot water heater and soon my Pex manifold, isn't huge, so I might need to get a little creative here.

I completely understand what you're saying about the wye.

The dampers you are referring to are actually built into the ductwork itself, right? Not louvers at the grille?

Do you think I can get away with 12" round or would you stick with the 14"?

Garasaki

Yep they are just a round piece of sheetmetal the same diameter as the duct, with a tab and handle stuck on the side. You drill a single hole, stick the piece in the duct, slide the tab thru the hole (from the inside of the duct outward) then attach the handle to the tab. Takes 30 seconds at most. THen you just adjust the handle to rotate the piece of sheetmetal in the duct. When the handle is perpendicular to the direction of airflow, the piece of sheetmetal is sitting across the duct filling almost the entire thing. When the handle is parellel to the direction of airflow, the piece of sheetmetal is just a thin sliver the air flows right over.

Well right now the whole system is served off a 12x8 duct right? Well a single 12" round duct has more area then a 12x8 duct. So it will undoubtedly still be an improvement.

stubits

The more I talk to you guys the more I realize just how poorly designed my current system is. It's more than just a little frustrating, although not nearly as frustrating as the basement bathroom that was installed without vents and traps. That was fun!

Little by little I am figuring things out. We love the house, but hate the flippers. I am sure I'm not the only person to ever say that.

Well, it sounds like there's some hope here. I am excited to try and resolve this problem, but will wait until the temps warm up a bit. I need to open the ceiling in the utility closet and some walls on the main level to install new hot and cold water lines (getting rid of the galvanized steel pipes, the only issue I really planned on having to fix).

Does my plan sound reasonable? At least so far?

How hard is it to tie this all into the plenum? Running the ducts will be easy, straight shot from the utility closet up to the living room and dining rooms, maybe 10 feet each, so no big deal there, but how hard will it be to get it all tied in?

Also, inevitably there are going to be a couple of 45's and maybe a couple of 90's. How much of an impact will that have? The runs will be really short.

Garasaki

Actually you could do a lot of this while it's cold out. YOu can definately run all the new return branches, and bring them back to the furnace. Then make the final connections later.

It won't be hard to tie these in. Especially since they will be larger diameter circles. The worst part might be dealing with the cramped spaces.

You'll no doubtedly have some elbows. Each elbow is sorta like adding 5 feet of straight duct. Again, compared to what you have now, it will be a major improvement. Take your time laying it out and planning it, and measure carefully when you start cutting. You'll be golden. It may help to pay attention to duct runs you see elsewhere - grocery store, local bar, free treatment clinic (lol J/K), etc. The pro's lay stuff out very neatly - try to emulate what they do.

stubits

And when I tie it into the plenum, all I do it cut a hole using some tin snips and then use a take off collar to connect the round duct?

integlikewhoa

Everything said above sounds great. Its not hard to tie all this in to the plenum.

Mine was made for free as a favor from a friend, but dont quote me on this but probley less then 100 for a custom plenum from some one that does sheet metal. They sell premade ones and you can see if they fit your filter opening properly, but mine didnt.

You should go with 2 14" atleast. or like I said before 2 12" and one 9" or so. If you go with 2 14" dont wye them from (2) 14" down to (1) 14" that dont do any good. I'll see if I can find some pics of mine, but I wyed 16". so it was a wye 16x12x12. If not you get something like a 16x16x16 and get (2) 16x12" reducers.

So if you can get some sizes and pics of the plenum and a wide shot around the plenum so we can try and see how much room we have to work with and what will fit.

Also I didnt look threw your manual again, but there should be some DIP switchs in the heater to slow down the blower. Since your unit is over sized this might be a good idea. Im also not so sure why you have a 5 ton blower/heater 4 ton coil and 3 ton a/c unit. This im sure will play a bad part into the efficiency.

Just work with you have and try to make the best of that and you should be good.

stubits

Sounds good to me.

I am guessing the mismatched components are just whatever these losers could get their hands on cheap and easy. You'd think people would want to take pride in the work, even just a little, but I think for so many it's only about $$$.

integlikewhoa

Heres an unfiinshed pic of a return plenum. it has 2 12"s into one 16" for the grill in the hallway 6" fresh air from outside 10" for the bedrooms and 12" on the bottom as a bypass.


Everything Just bearly fits. The other plenum looks the same. With 2 12" and 2 9" for the house and 1 12" for the bypass.

stubits

These photos are great, really, really helpful. It’s great to see how a system is designed as I don’t really have much to compare my system with. I haven’t had a chance to get good photos of my system yet (I took some, but they don’t really show much), but I think this might just work.

What do you think of this? Can I get a wye that is 16x14x7? If so, my thought is to attach two of these to the plenum, running both the 14’s up to the main level of the house, one to the living room, one to the dining room. I’d use the remaining two 7’s to add two return vents to the basement, one in the bedroom and one in the living room area. Or, if I am doing this, could I get away with two 12’s to the main level? Of course I’d keep the 12x8 running to the second floor. What do you think? It would have to be a major improvement, but would it be sufficient in your estimation?

Also, any thoughts on oval ducts? Just looking at them, it seems like I could use the full width of my floor joists while minimizing the protrusion into the various rooms. That said, oval duct doesn’t seem quite as easy to come by and the connections might be overly complicated, but nevertheless would appreciate your thoughts.

I think I have a good idea of how to connect this all up at the plenum, but what about at the register itself? Can I run a straight line up, cap it with a 90 and tie that 90 straight into a register? Would something like that work? Assuming I am running 14’s up to the main level, what should the dimensions of the register be? What about the grille?

So, this all started because the current main level vent makes so much noise. By increasing the number of vents and ductwork, less air should be pulled from each vent and the noise all around should go down, right?

Some more logistical questions, if you don’t mind.
1)Can I get most of these pieces stock at either a big box store of an HVAC supply house? Or am I going to have to get a lot of stuff custom made?
2)What Sorts of tools will I need? A pair of tin snips for sure, a good pair of gloves I bet, mastic and tape, but anything else? Do I need something to crimp the ductwork? Any special tools to cut the plenum holes correctly?
3)How do I go about securing the ductwork as it runs up vertically? I am sure there must be straps of some sort. How often does it need to be secured?

Oh and at some point you mentioned something about settings on the furnace itself. I looked through the manual but either didn’t see anything or didn’t understand what I was reading. Is it possible to lower the CFM’s through some sort of setting?

Oh and I did a bit of research on the mismatch of equipment and it doesn’t seem as bad as originally thought. First, the AC compressor is only 3 tons, so not horribly oversized for my house (oversized for sure, but not as bad as 5 tons would be!). And I read a number of sources that actually indicated that you can improve performance of the system by having the AC coil a half ton or a ton larger than the compressor, apparently it makes for greater surface area. Of course it is crazy that my furnace/air handler is 5 tons, 100,000 BTU, but what can you do.

Finally, do I see PEX in your photo? If so, did you do that yourself?

Thanks for everything!

integlikewhoa

16x14x7 would work but 16x14x8 would be better. The 2 smaller should flow the same as the bigger side. Also your going to have a hard time finding weird sizes. You'll have to use reducers possibly. No you should use 12's stick with 14's. Also if you do end up going 12's you dont need a 16" on the plenum. I say that cuz a 12" and 7" don't flow enough for you to need a 16"
Never delt with oval? do they even exist? You need to insulate your duct work. Leave room for that. I think you option is either round or rectangle.
Yes should work. Where are you installing a grill? In a wall floor or celing?
Also a grill and register is the same. You will need a what they call a boot or celing or floor box. This will connect to the duct, screw to the studs and provide and box for the register or grill. A register is used on the output side and uselly hase louvers that open and close or can point in different directions. You wont need those for returns. You need grills. You can buy grills with filter build into them, that you remove and replace when they are dirty or you can but them with no filter if you have a filter down on the unit. Need to know with or without filter and for sure what size duct your going to have to see a grill size.
Yes correct. the noise comes from the speed the air is traveling. Since the duct is to small the air has to travel fast to try and get so much threw. The bigger duct size used the slower the air goes.
Same goes for when you pinch the end of a garden hose or cover it with your thumb. The water shoots farther. Theres not more water comming out, theres actually less. But since you pinched or covered the end of the hose the water shoots out further cuz it has to speed up to fit the water threw a smaller hose or hole. Bix box stores suck at Duct supplys and they wont have any big parts. maybe small 8" pieces and small register covers. You need to find a HVAC supply store. they will have everything.

There is a nice tool that hooks to a drill and cuts circles in the plenum. I bought mine at home depot, but HVAC probley cheaper. Youll need soem self tapping screws to hold the metal parts together before you tape and mastic them.
HVAC store will have a strapping like plummers tape.( metal cut to lenght with holes in it, but its wider).

Well most do have some setting but mine is a brand new 95% dual stage unit, so maybe it has more options then yours im not sure. But inside the heater on the main control board where the wires hook up there should be some DIP switchs that can be changed depending on different settings for you unit. Mine has different blower speeds for each stage of heating and cooling. Im thinking your might have something like that. It should be in the install manual or writen inside the unit on the back of the door or somthing. I figured maybe you could turn down the CFM, to match the house and save some electricity. Im not so sure on your unit how it works.
OK. youll be ok. Not saying throw everything away and start over you can make this work. Also maybe you need the heat more then the A/C in your area. I need more A/C then heat here.
Yes thats 1/2" pex. Yes pex myself and it is eaiser then the A/C work. That pex was run up into the attic for the Humidifier. I ran it next to the drain comming up an interior wall going down to the crawl space below.


Also you can check out this website, to see whats out there and send links of parts you want to use. http://americanhvacparts.com/duct-work.htm

stubits

Sounds great. I will stick with the 14's and go with 8's for the basement returns.

How far do you think a 16" 90 would stick out from the plenum? Based on your experience? Trying to figure out what would be sufficient clearance.

They do have oval ducts, but not so common, so I will avoid. Do I need to insulate the return air ducts? I know the supply ducts need to be insulated. Good to know, if that's the case!

Thanks for clearing up the confusion on the grill/register issue. All of the return I am doing will end up being on the wall I think. What size box will I need of the 14s? How about for the 8s? How deep are the boxes? Just making sure I am going to have enough room in my design. How about the grilles, what size would be appropriate?

Is your whole house PEX? I am getting ready to repipe the whole house in PEX. We currently have 75 year old galvanized steel which has caused really awful flow throughout the house. I think I'll combine the ductwork with the plumbing project as it involves some of the same walls. Any suggestions on the PEX? It seems pretty manageable to me.

Thanks!

integlikewhoa

Probley around 20-24" or so with the starter ring.
Sure the oval is not for furnace exhaust or hot water heater exhaust like double walled? Thanks all I have seen around here.
Insulate if its not in a conditioned room. Mine is in the attic. It gets over 110 up there in the summer and the return air will be the same as in the house. So I dont want the return pipes to turn 100 degress and heat up the return air. So if your unit sits in a place thats condition and all the pipeing is inside the conditioned parts of the house then your ok. Same goes for you in the cold. If you unit sits in the basment and its 30 degrees or less down there and your running the heater the return air in the pipe should be 70 degrees. You will want to insulate it.

Different boxs are different. you can do any of these types.
http://americanhvacparts.com/Merchan...stackhead_boot
http://americanhvacparts.com/Merchan..._perimeter_box
http://americanhvacparts.com/Merchan...duct-cone_boot
http://americanhvacparts.com/Merchan...uct-floorboxes

Just browse threw the site and youll get some ideas on what is what and what will work for you app.
My house isn't all in pex now. What I did is got the manifold setup off the main line and I'm slowly adding new lines to the manifold (with valves) as I remodel each room. So I'm half and half now. I redid the main line when I bought the house and that enters the house in the crawlspace and splits off to the old galvinized and the new pex. Eventually I'll cap off the part going to galvinized when everything is moved over.