I bought a stronger fan to vent our bathroom shower to replace a smaller one that was vented through the roof. The newer fan has a larger opening (i think it is 3 1/4 by 6) and cannot use the old flexible ductwork. Access to the crawl space is not existent.
What is the best way to vent the new one through the existing roof vent (solid ductwork or flexible?)
thank you in advance
You most likely have a 4 flex tubing, and your new vent has 6 opening. There is a variety of reducers out there. Pick up an adapter from 6 to 4 and use it to attach to the original tube.
masterjoe,
doesn't the reducer limit the venting power of the fan? I bought a stronger one because our bathroom need it. i wouldn't want to limit it.
also, i am having trouble connecting the flex tube to the 4 adapter, is there a trick to this?
thanks
You're indeed reducing the cfm rating of the fan by 33%, I agree. However, it depends on how far that run is from the vent to the roof. Reduction may not be sufficient enough to worry about it.
Also, there must be a flapper at the vent opening to prevent the backflow...right??
The right way to connect tubes is to use a Al tube nipper, which permanently indents two tubes and joins them together.
However, I usually slip one over the other and screw in a couple of sheet metal screws around the overlap.
The run to the roof is about four feet.
When you mention using an Al nipper to join the reducer to the flex tube, I think the flex tube is not made of metal. I was thinking about using duct tape to join the two. How does that sound?
Personally, I would get rid of the flex pipe - this stuff should be banned from the face of the earth. You are about to compromise the capacity of the fan by increasing the static pressure it has to overcome in the reductiuon from 6 inch to 4. Don't add to the problem with the flex duct - this material adds significantly to the static pressure in the system. Can you reach the connection at the roof, and if so, I would install metal duct.
yes i can reach the vent in the roof but only by sticking my head through the ceiling in the bathroom with the fan removed. There is not crawl space opening to give me access to the area above the bathroom. However, I was thinking about making an access area.
The problem is we have tongue and groove finished wood covering the walls on the second floor above the bathroom. Cutting into them with lath and plaster behind them, sounds messy. Plus, what do I put in it's place? A small door?
do you have any suggestions
thanks
Sometimes, its best to step back and take another look at the situation. Can you get to an outside wall by going horizontally? How far away is it?
I vented the old fan through the exterior wall but I was never happy with it. I used one of those dryer vents with the louvered slats that close when there is not air flowing out through them. The problem with that was that I installed the vent on the fascia board under neath the over hang eaves and because the board is at a slight angle to the ground, the louvers stayed open all the time. I was a little worried about pest infiltration.
So, I reshingled my roof recently and put in a big vent (probably 10) and attached the flex tubing from the old vent fan to it. Then, I changed to the bigger unit and I have been unable to attach the existing flex tubing due to the wider opening in the new vent fan. I know I can get the reducer but vent up to the roof without the crawl space. And if I make a crawl space (which I don't relish given the age of the house) I am not sure I know finish off the opening so it looks nice.
What do you think?
thanks
You definitly want the duct connected on both ends. You mention the installation of a roof recently - is it possible to work from both ends. Get the reducer, install it at the fan and push this up into place in the ceiling. Go up on the roof a carefully remove the shingles around the vent, remove the vent, reach down in and grab the flex duct (I hate the stuff but sometimes ya gotta do what ya gotta do) and bring it up through the hole in the roof and attach it to the vent, then replace the vent. The flex duct would have to be sized long enough that you can get it through the roof but not so long that it sags as it goes up.
Another option (I spend a lot more time on home improvements than I should) is an iteration of the above - except use metal duct. Put an elbow on the fan to turn the outlet up and maybe, a 2 ft piece of metal duct on the elbow. Put the whole thing in the ceiling and then go up on the roof and remove the vent as above. You should be able to get a fairly accurate measurement for the piece of duct needed to connect the two.
Will take a bit of screwing around but in the end, it will be worth it.
I agree that venting to the underside of the soffit is not the best idea.
No easy suggestions for getting access to the crawl space other than opening up the wall and installing a removable panel. I have the same situation except I custom made a small raised panel door and installed a jamb and casing just like a full size door - but that's a lot of work
All of Dave's suggestions are indeed good ones; and the most desirable ones. However, my experience with bathroom ducts indicate that venting warm and moist air to the outside is not TOO critical that you have to lose your sleep over.
How big is your bathroom?? 6 opening tells me that the fan that you bought is a dual unit with lights, isn't it??
CFM rating on your fan strictly depends on the size of the bathroom. Overkill is better than underkill; however, if overkill will give you too much headache, it ain't worth it.
You said your other bathroom fan has 4 ducting, right??
I don't know the size difference between your two bathrooms but it kinda tells me that the current fan that you have is an overkill.
If you really want to install that fan, you should follow Dave's suggestions. I cannot encourage you to downgrade CFM rating of your fan(I only think that it's not that big of a deal).
I'm just suggesting that there is always an option to get your current fan exchanged for one with 4 duct opening.
Masterjoe's last suggestion is an excellent one and may get you out of the prediciment your in. However only you know the exact conditions you are faced with. I have a tightly sealed house and I went to a larger (more expensive) exhaust fan because the one I had, Coupled with the crappy installation done by the builder (Flex pipe) wasn't doing the job. We had a terrible problem with mildew. When I remolded (complete gut job) the bathroom, I tore down the ceiling and found out why the fan wasn't doing the job - even though it was vented directly to an outside wall 4 feet away. Somehow the flex pipe he used got kinked so the opening was reduced to less than 1/2 of what it should have been. Since the fan was 20 years old I replaced it and vented it to the same location - but, I used metal duct with Taped joints. Been two years now, and not a hint of any problems - no condensation on the walls, and I can even see myself in the mirror.
If your bathroom is of the average size and considering your within 4 feet of the roof, I would opt for a fan with a 4 inch duct.
One last comment - you mention the roof vent - I hope you are connecting the vent directly to the vent - not just placing it near the vent.
here is the whole story:
the original fan was not doing the job. it was small with no light. the mirror would steam up and the room as well. so, i went with a bigger unit which i think moves 170cfm. it has been great but is not yet vented to the outside (which i know is bad for the insulation and framing). hence, me wanting to vent it.
the old fan had the 4 (i am guessing at this dimension but it seems logical) round flex pipe vented up into and beyond the lip of the roof vent. the flex pipe is still connected to the roof vent but i couldn't connect it to the 3 1/4 x 10 opening in the new fan (which has a light as well as a fan). I am thinking about doing the reducer and attaching the flex tubing before I install it back into the opening.
what do you think?
170 CFM is more than double the capacity of 'normal' bath fan(70+CFM). If you really prefer to use it with the existing 4 ducting, please double check the flex tubing for any obstruction similar to the one Dave described. Remember, 170 CFM fan won't vent out all 170 CFM due to reduced ducting. It will be less.
Thanks. I'll try it.
3.5 by 10 inch is 35 Sq inches. 4 inch round duct is 12.5 Sq inch - about 1/3 of that which the fan is designed for. This will raise hell with your static pressure, thus reducing the air flow from the fan. It is an expontial function and the end result will likely be not much better than when you started.
so in other words, it is metal ducting or nothing?
The reduction from the 3.5 by 10 inch rectangular outlet on the fan to a 4 inch round already compromises the situation significantly. The use of flex duct adds to the problem - I would not use it.
The performance of this fan will be so far off the charts, you can't predict the results. Assumming the fan can overcome the static pressure - which it can't, the velocity through a 4 inch duct will be 1950 ft per minute - way way in excess of duct design velocity.
They make roof vents specifically for venting baths and range hoods. If it were me, I would look for one of these and think very carefully about how difficult it would be to go up on the roof, remove what you have, and install the proper vent. The vent line from the fan must be connected directly to the vent - not placed near it or in it.
the flex tubing that is there is stapled or nailed into the vent in the roof. the guy who replaced my roof last year attached it.
if i hear you correctly, i should use metal and not reduce it. the only problem is getting access to the crawl space. i have never made an access door before but if i need to, i will have to learn.
there is a built in shelving unit on that side of the house that i was thinking i could remove and replace after. i can't imagine trying to fit the ductwork down through the roof given that the opening in the roof and the vent in the bathroom, don't line up. so i would imagine that i would be doing a lot of angles to make them both meet.
if you think i am thinking about the right thing, please let me know and i will go ahead with it.
thanks again
Your latest plan involves many angles, you mentioned??
That involves using elbows; and it reduces CFM capability as well.
You just have too many obstacles to properly install that 170CFM fan and get the most out of it.
Again, why not taking it back to the store and exchange it for the one that will fit and save you unnecessary headaches??
i appreciate your feedback but i am confused. why is overkill not a good thing here? if the fan is too large and powerful for the space, why can't i just work around that? isn't it better than having one too small.
i realize i will not get it's fullest potential, but it has got to be better than a smaller one. the one that i had before, did not do the job at all.
thanks again
I understand your frustration with your old fan that didn't do Jack.
I had a similar problem and I ended up spending $90 and bought the decent fan(110CFM).
What I'm driving at is:
Overkill is better than underkill; no question about it.
But, 170CFM fan with 4 duct(+ elbows) is like having a corvette engine on a lawnmower. Your infrastructure(ducting) won't handle the capability of your mighty fan.
Since the duct won't deliever and dissipate all volumes of air that your fan discharges, there'll be a back pressure building up which may exert a strain on your fan's motor.
Bottom line is: It's your bathroom and it's your project.
But, I'm just giving you some friendly pointers to consider.
I appreciate your help. REally!
And I understand the concept of the corvette engine on a lawnmower, but I was hoping to do what I can with the ducting so that the engine stays in the car and not on the lawnmower (are we getting too abstract?). Anyway, metal ducting with only a few ells (or angles) would allow the fan to vent to it's capacity with little resistance.
I am leaning toward accessing the space because it would be good to have some regular access anyway for future use. I just don't want to ruin the tongue and groove original woodwork that i have on the walls of the room above the bathroom.
I can't return the fan because I bought it a year ago and I have been using it for that long. I didn't want to have to admit to this but: I have been venting it into the crawlspace for a year without connecting it to the roof vent. I know this is a no-no so please don't beat me up too badly.
thanks again
Look, if I were you and I made the decision to get into the crawl space, I'd go with somewhere near the correct doct size. take a trip to a roofing supplier and check out what is available in roof vents. and go from there. HD usually has a good selection of ductwork, including adapters, elbows, etc.
Also realize that if you are trying to exhaust 170 CFM from the bathroom, ya gotta make it up somewhere. That is you have to get that much air into the room or the fan just pulls a slight vacuum and nothing moves. The easiest way to do this is to keep the door open a crack or cut he bottom off so you have a gap at the bottom. - 3/4 to 1 inch should do it.
thanks again. i will get the correct duct work and the door already has a 3/4 to 1 inch gap underneath. it is definitely pulling enough air.
thanks again
Best of luck to you on your endeavor!!
Pls come back if you need more help.
Tags: vent, bathroom, through, roof, crawl space, flex tubing, roof vent, better than, thanks again, flex duct, have been, metal duct
