bath exhaust fan venting material

[howardrichman]

I'm installing several bath fan vents using a Fantech dual vent remote fan using 6" ducting, and two 110 cfm Panasonic units using 4" venting, multiple switching in two bathrooms. I'm not sure if two 4" pipes in one 6" roof vent will open the flapper if one 4" is pushing air. I'm also told there's a building code requirement to install a 8 R rating insulated pipe from these vents directed to the roof. Is hard pipe, aluminum soft, or ridged flex still permissible even though it doesn't meet r value requirements?

HR...

 

[jxofaltrds]

I'm installing several bath fan vents using a Fantech dual vent remote fan using 6" ducting, and two 110 cfm Panasonic units using 4" venting, multiple switching in two bathrooms. I'm not sure if two 4" pipes in one 6" roof vent will open the flapper if one 4" is pushing air. I'm also told there's a building code requirement to install a 8 R rating insulated pipe from these vents directed to the roof. Is hard pipe, aluminum soft, or ridged flex still permissible even though it doesn't meet r value requirements?

HR...

I think that you answered your own question. No.

 

[John120/240]

Sounds like a problem for the tin knockers to me.

 

[howardrichman]

I'm responsible to install the noted bath fans. All I'm asking is, do I have to use the R rated flex to meet building code, or are other types permitted.

HR...

 

[J.P.]

I put in a couple of bath fans in a new office build. I talked to the heating guys and asked
your same question.

They said it was ok to join two fans even using the same size pipe. I had to build my own Y pipe, but it worked fine.

We vented through the side of the building with 4" but your fans are bigger than mine. I think mine were 89cfm or something like that.

 

[howardrichman]

I put in a couple of bath fans in a new office build. I talked to the heating guys and asked
your same question.

They said it was ok to join two fans even using the same size pipe. I had to build my own Y pipe, but it worked fine.

We vented through the side of the building with 4" but your fans are bigger than mine. I think mine were 89cfm or something like that.

I guess you could bring two pipes to one vent if the max allowable cfm for that output vent is not exceeded, and the airflow will allow enough lift to open the flapper.

HR...

 

[Gregg Harris]

I'm installing several bath fan vents using a Fantech dual vent remote fan using 6" ducting, and two 110 cfm Panasonic units using 4" venting, multiple switching in two bathrooms. I'm not sure if two 4" pipes in one 6" roof vent will open the flapper if one 4" is pushing air. I'm also told there's a building code requirement to install a 8 R rating insulated pipe from these vents directed to the roof. Is hard pipe, aluminum soft, or ridged flex still permissible even though it doesn't meet r value requirements?

HR...

R8 would not be required on exhaust duct, but it should be insulated to prevent condensation before exiting the termination.

 

[Gregg Harris]

I'm installing several bath fan vents using a Fantech dual vent remote fan using 6" ducting, and two 110 cfm Panasonic units using 4" venting, multiple switching in two bathrooms. I'm not sure if two 4" pipes in one 6" roof vent will open the flapper if one 4" is pushing air. I'm also told there's a building code requirement to install a 8 R rating insulated pipe from these vents directed to the roof. Is hard pipe, aluminum soft, or ridged flex still permissible even though it doesn't meet r value requirements?

HR...

R8 would not be required on exhaust duct, but it should be insulated to prevent condensation before exiting the termination.

 

[RLyons]

Curious as to why Panasonics and fantech, how long is your run? Fantech makes a recess light vent kit for this installation which would be cheaper.
http://residential.fantech.net/residential-products/bath/dual-grille/

 

[ptonsparky]

Condensation is a bummer, especially if you have to pay for the repair of sheetrock and rework to make it right. Ouch.

 

[GoldDigger]

What is not allowed is for two fans to combine their outputs into a single duct.
For condensation, look at the slope of the vent to make sure that the condensation does not run down to a joint or other possible point where it could leak out.

Tapatalk!

 

[ramsy]

Condensation is a bummer, especially if you have to pay for the repair of sheetrock and rework to make it right. Ouch.

In my area a flat rough-cut piece of wood is often found under exhaust vent outputs, in most original construction. The board is usually stained from years of dripping condensation & evaporation.

 

[GoldDigger]

Current codes require that the vent exit through the roof or exterior wall. No place to put the board.

Tapatalk!

 

[goldstar]

What is not allowed is for two fans to combine their outputs into a single duct.

Never knew that was not permitted. I've done this dozens of times but you have to use back flow preventers for each feeder duct. I would be concerned about the flapper opening when venting from a 4" duct to a 6" duct. Also never had a condensation problem that I was made aware of but that's not to say that one didn't exist.

 

[iwire]

Here in MA electricians are not allowed to do duct work.

Life is good.

 

[A/A Fuel GTX]

Here in MA electricians are not allowed to do duct work.

Life is good.

The way it should be! When I do a new house, my bid always states " venting to be performed by others ". I install the fans and that's it. I believe HVAC stands for Heating VENTILATION and Air Conditioning.

 

[mjf]

Here in MA electricians are not allowed to do duct work.

Life is good.

The way it should be! When I do a new house, my bid always states " venting to be performed by others ". I install the fans and that's it. I believe HVAC stands for Heating VENTILATION and Air Conditioning.

That all sounds fantastic for commercial, new construction and even a remodel where other trades are involved.

I doubt you'd ever get a residential job adding a vent fan to an existing bathroom if you excluded the vent.

 

[kwired]

The way it should be! When I do a new house, my bid always states " venting to be performed by others ". I install the fans and that's it. I believe HVAC stands for Heating VENTILATION and Air Conditioning.

Last new home I did, which was two years ago, the HVAC guy did run flex duct to my bath fans, but I removed it and ran larger sized rigid flex duct and he asked me why? You would think that an HVAC guy that is supposed to know how many CFM a particular sized duct is designed for would know that a fan with a 4" outlet but a rating of 110CFM needs more than 4" duct to handle 110CFM. By putting too small of a duct you reduce the CFM, and also increase noise from the fan, and flex has more resistance to air flow than rigid duct has, he then replies with "but the fan only has a 4" outlet" to which my reply is something like "how many times do you leave an air handler and immediately increase the main duct to a size larger than the outlet of the air handler so that you don't lose available CFM through your duct"

I'm not even an HVAC guy either, but sometimes wonder if I could do it better than most HVAC guys I run into:angel:

 

[kwired]

What is not allowed is for two fans to combine their outputs into a single duct.
For condensation, look at the slope of the vent to make sure that the condensation does not run down to a joint or other possible point where it could leak out.

Tapatalk!

Why can't you combine two into a single duct, in general anyway? I can see circumstances where it may not be desired or even allowed. Increase of size of the single duct is probably a good idea so you don't lose CFM ability when both are running. Backdraft dampers are usually included with the fans so pumping air into a second room shouldn't be much of a problem, they are generally not a positive sealing damper but will stop a pretty significant amount of reverse flow. If you have a remote exhaust with duct to multiple rooms .... you combine all those into one outlet duct.

 

[growler]

Here in MA electricians are not allowed to do duct work.

The way it should be! When I do a new house, my bid always states " venting to be performed by others ". I install the fans and that's it. I believe HVAC stands for Heating VENTILATION and Air Conditioning.

That all sounds fantastic for commercial, new construction and even a remodel where other trades are involved.

I doubt you'd ever get a residential job adding a vent fan to an existing bathroom if you excluded the vent.

I admit that a lot of these fan installs do go to electricians but they really should go to the HVAC contractors and electricians called in as needed.

Even here if any hard ducting is needed an electrician can't pull a permit for it so an HVAC contractor is needed. They mostly let a little flex ducting slide ( residential ).

We can't get a permit to install an electric water heater either.