Bathroom exhaust fan
Have an old house with no exhaust fan in the bathroom, and it looks like quite a job to get electric there and to fit the fan in the wall or ceiling. Looking for alternative avenues to take, does it really matter if the intake for the exhaust fan is on the ceiling/in the wall/in the floor? I was thinking of installing an in-line fan 2 floors below in the basement and running 3 or 4" PVC piping up to the bathroom (which is doable) along with the electric, but is this a viable arrangement?
I submit the hypothesis that it will work perfectly well, and ask for any pro who knows otherwise, to tell us why. I am a homeowner so have few "credentials" in this department. I do know there is at least one toilet manufacturer who has a 10 cfm fan in the bowl, their idea is to remove odors at the source with minimum airflow.
Originally Posted by Jimski
Fan manufacturers emphasize getting to a certain number of air changes per hour (ACH) and I believe that is most important whether you are trying to control odor, or homogenize humidity in the house. My own master bath suite has a tendency to high humidity and I have become convinced that 3-4 ACH added ventilation will fix this (there remains a question in my mind about makeup air, in my hot-humid S.Texas climate). Speaking as a homeowner who has done his best to understand this, I suggest a floor or wall vent will be effective in your bathroom if you have sufficient air flow.
There might be contrary arguments, but let us hope some other professionals will articulate those.
If you can use 4-inch piping, that will have almost twice the area of 3-inch and might keep air speed within the recomendations made by ACCA Manual D. It will depend on the CFM airflow you push through this channel, but many bath fans are sized in the 80-120 CFM range.
Best of luck -- Pstu
Your advice is extremely well put--and equally well taken. As I stated, it is an old house (circa 1875) and as such it has 4 smallish bedrooms and 1 even smaller bathroom (apx 5' x 6') so it probably does not require a whole lot of CFMs to clear away the steam-like humidity caused by the shower. Perhaps a 3" or even 2-1/2" PVC pipe with an in-line fan?
If I were designing this, I'd throw in a 75CFM fan and a 6" duct discharged to the outside. Intake is usually done by undercutting the door by ~1 inch so that becomes the make-up air path. My $0.02.
I am glad to share what knowledge I have that is true and correct, however this being a contractor's board we might run afoul of the DIY rules with some of the "wrong" questions and answers. This is another board where you can float your same question and receive additional help. Some of the same professionals on this board, also will help DIY-ers at this site:
Originally Posted by Jimski
Here is a simple web page that one vendor offers to size a fan. It suggests a minimum 30 cfm for your bathroom but there might be a problem buying one that small:
Fantech is a highly respected maker of remote fans, however the smallest I know of is 100 cfm. Lots of people in the HVAC profession seem to favor Fantech.
I myself am a homeowner in a hot-humid climate, which implies I might not be fully aware of some "gotchas" to know about your cooler climate. So please try to verify whatever I say before you plunk down your money and cut through anything... I have a Panasonic 80 cfm in my toilet stall about the same size as your bathroom, and it works great for me. However it is a ceiling model and I know you want a remote fan. My Panasonic came with an adapter for 3-inch duct so I guess they endorse that but I used 4-inch -- I rather think it will not flow 80 CFM if one uses 3-inch duct.
Let me just observe that ACCA Manual D recommends air speeds under 1000 feet/min (FPM) when using hard pipe like the PVC you propose. The limit is lower if you use flex duct. Friction within the duct will increase with air speed, that will reduce any fan's output and that is one reason you want to keep FPM from being excessive. You might want to consider a 50 CFM fan which is about the smallest rating size you can easily find. A 4-inch duct would result in ~570 fpm while a 3-inch would result in 1020 fpm. At some high airspeed the air will become turbulent, resulting in noise and friction, I will not claim to know how high you can push it. Someone with more experience would know better.
Hope this helps -- Pstu
Very interesting, I must admit. When I get to work tomorrow I will run it by the tinknocker foreman. Although neither of us do residential work, perhaps a common solution can come of it. How people lived in this house ALL these years without an exhaust fan in the bathroom is truly beyond me.
If all else fails, I may try to run the PVC, or possibly round duct, and figure oout the fan's placement in the basement later.
Bathroom exhaust fan
To properly ventilate a bathroom, the exhaust point should be high, not low. Warm air rises and brings humidity and odors with it. The steam in my bathroom gathers towards the ceiling, not the floor. For my second floor bath, I installed an exhaust grille 4" from the ceiling on a wall away from the door, connected to a duct running down through the wall to the basement, then to an ERV. I also picked up one in the general kitchen area (again high) for cooking odors and humidity. Fresh air comes back into a ducted return plenum. I have "make-up" air for what I am exhausting with energy recovery. I have an automatic "whole house" control and will install on-demand switches at each exhaust point. We did the same concept in my rental house.
I like your system, sounds reasonable. I would also like to install a whole-house fan for summer. But I have no duct work at present (hot water heat) so what ever I install it must comply with what is there, within reason. Any ideas?
My first house had no bath exhaust fan. We just opened the window.
That worked just fine. My new house has no bathroom window, so we use the fan it does have.
Remember, Air Conditioning begins with AIR.
I have two bathrooms with windows but with no fans. Our local climate makes ventilating with the window confined to a narrow band of days in spring and fall. In one bath I intend to fur down part of the ceiling over the shower and commode, install an exhaust fan straddling each, and duct it out over the window if there's enough room above the header to send the duct over it and through the exterior siding. The other one already has a fur-down and a wood wall on the exterior, so likely no headers to deal with.
One thing I will NOT do is vent the fan into the attic. Such is a no-no.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
So you exhaust the bathroom air through an HRV?
Originally Posted by Drippy
sounds like a good system. just 1 question: did you place the return plenum in your bathroom as well? i think it would be better to place the return plenum in your bedroom, and so creating an airflow in house: good,fresh air in bedroom going to bathroom and then outside.
What is your experience when buying a exhaust fan. Can you share? And what is the best price do you suggest?
To properly ventilate a bathroom, the exhaust point should be high, not low. Warm air rises and brings humidity and odors with it. The steam in my bathroom gathers towards the bathroom exhaust fans
, not the floor. For my second floor bath, I installed an exhaust grille 4" from the ceiling on a wall away from the door, connected to a duct running down through the wall to the basement, then to an ERV. I also picked up one in the general kitchen area (again high) for cooking odors and humidity. Fresh air comes back into a ducted return plenum. I have "make-up" air for what I am exhausting with energy recovery. I have an automatic "whole house" control and will install on-demand switches at each exhaust point. We did the same concept in my rental house.