Flex duct connectors

TREEBARK · 11-09-2011, 01:06 AM

I understand regular flex duct connectors (splices) have beads allowing for good connections, but what do the pros do when you go from one size either up one or down one (16" to 14" or vice versa) in a trunk run and a wye is not where you want to make the transition? Regular reducers are smooth and aren't they really for metal to metal connecting? Thanks.

**beenthere** · 11-09-2011, 05:09 AM

Use a regular reducer, duct bands, flat washers and screws, along with mastic.

Doc Holliday · 11-09-2011, 08:53 AM

Not just for metal at all.

TREEBARK · 11-09-2011, 04:40 PM

Thanks for the response, I just did not know as I was thinking about code of what is acceptable and not as the splices are specific for flex duct right, but I have been told guys use regular metal pipe and cut it and make it for splicing, but I assume that is against code or maybe not. I have a 12" duct that is just taped up together at the extended 25 ft point and I am sure that is against code also.

Anyway, my other questions are what do the pros do for example, you have a 6 inch flex duct going to a 6 x 10 boot and you want to, as I do reduce that 6 inch flex duct down to 4 inch. Do you connect a 6 to 4 inch reducer at the wye and again at the boot or do you change the wye and the boot, which would obviously require redoing sheetrock work which I want to avoid. If your wondering why, I have this setup in the tiny toilet room sized 3' X 4' and I see it as being very inefficient and so I want to increase my duct one size in my master closet as it has a 6" duct which I know is 75 CFM, but my manual d calculations says I need 180 CFM and it is always cold in that room. By the way, it also says I need 13 CFM in the toilet room, but I can't find what the CFM of a 4" flex duct is, but 5" is 50 CFM, which is still way more than what I need and I really don't understand why there is a register in the toilet room anyway unless code requires it, but it couldn't require a 6" duct that is for sure. Thanks, RC.

**beenthere** · 11-09-2011, 06:02 PM

Run 6" all the way to the bathroom, and use a balancing damper at the trunk/wye to control CFM.

Cutting a 6" pipe to use as a splice is fine, and not against code here.

TREEBARK · 11-09-2011, 06:57 PM

I wished I could, but without going more in depth, my system is way over in DSP because of my coil alone. So, which adds more to the static load the damper or the reduction size of the duct. Either way, can you still tell me if you did reduce the duct size, would you replace the boot or not? Thank you again for your time.

**beenthere** · 11-09-2011, 07:10 PM

The reduction increases pressure drop more.

If I decreased size, I would replace the boot, as the increase to go from 4 to 6 only adds resistance and creates turbulence.

TREEBARK · 11-09-2011, 07:31 PM

Sorry, if I am making you repeat yourself, but I am planning to do this in my other very small bathroom and want this to be right as it has a 6 x 10 boot also and your saying if I replace the 6" duct with a 4 inch duct, replace the boot with like a 4" x 8" boot? And the boot and the new grille would have less resistance and air turbulance, right? I probably should replace the wye too then to do this more correct as it is a 8 x 6 x 6 and it should be a 8 x 6 x 4 right? I sure like the idea of the damper the more I look at this. Thanks again.

**beenthere** · 11-09-2011, 08:12 PM

The damper is the better way to go.

Yes, a 4" boot instead of a 6 to 4" increaser. Reducers and increasers all add a lot of resistance/turbulence to air flow.

Marty S. · 11-09-2011, 08:50 PM

Would you put a run in a room that only called for 13 cfm beenthere?

TREEBARK · 11-09-2011, 09:14 PM

You know, the builder did this when we bought the home brand new and seems rather ridiculous, again I was assuming it was code requiring this as I know we may sometimes spend a longer amount of time in that room than we'd like, but being it has a door I figured it is considered a room that must be heated and cooled, tiny but a room. So, if you don't think it is a code requirement I could completely eliminate it all together. There is also an exhaust fan in there and thank god you can't hardly turn around in there, you might as well leave the door open. My wife is 5' 3" and 100 pounds and she avoids it and goes to our guest bathroom 95% of the time. So, I have no idea and I am open for interpertation here.
Thanks.

**beenthere** · 11-10-2011, 03:54 PM

Quote:

Originally Posted by Marty S.

Would you put a run in a room that only called for 13 cfm beenthere?

If the room(bathroom/half bath) is on an outside wall, yes. Unless the door has a fair amount of under cut on it.

TREEBARK · 11-10-2011, 05:18 PM

It is not on an outside wall it is surrounded by other rooms all the way around and it does have about a half inch under cut. So, being that is the case, do I have to have a branch in there? The other bathroom does have an exterior wall. Thanks again.

**beenthere** · 11-10-2011, 05:30 PM

nope, inside rooms like that don't need a supply.

TREEBARK · 11-10-2011, 09:56 PM

Great! Thank you so much! That is 75 CFM that I can get over there in that cold closet (about 12 feet away), but being there is a 6 inch duct running over there now and Manual D says 180 CFM is needed, can I move up to a 8 inch or two 6 inch branches. The master closet is the farthest NE corner of the house and is L shaped or trianglar in shape. What would you do there? Again, I am thinking about static pressure and I assume that two 6 inch ducts is a lot less efficient than one 8 inch duct, but I read that report from the environmental building science article that rooms should not have 8 inch duct unless they are high ceilings or are large rooms and this one has a 8 ft. ceiling and @ 90 sq. ft. floor area, but it is a closet and not a bedroom (if that makes a difference to you all). Thank you for your time as I am learning a lot here.