I’m installing an 80 cfm bathroom fan in a 1400 sf basement suite. The fan will be controlled by the normal wall switch and also by an interval timer. Either device can power up the fan. The suite is heated with electric baseboard heaters. Does anyone know of a guideline that would indicate how many hours per day the fan should operate in order to control humidity? I’m thinking about running it for an hour in the morning and an hour at night, but it’s a completely uniformed guess.
Thanks,
Scott.
PS.. we’re in Southern BC, a similar climate to Western Washington.
Replies
Canadian Building Code (1995) states that all rooms that you can live in to have 10cfm of supplied air! So your fan may have to run continous. In the colder area's where I am ( Manitoba ) usually means HRV (Heat Recovery Ventilator) is the only answer. For moisture control You should use a HUMIDISTAT to control the moisture. Talk to a heating-ventalating person and they should be able to help or contact the HRAI (Heating, Refrigeration, Air conditioning Institute of Canada ) and they should be able to .
Hope this helps!
IF IT WAS EASY, EVERYONE COULD DO IT!
Scott: I got to figgerin, You should have 1 air changes per Hr. , 1400 sf x 8 ft. ceiling (assumed) =11,200 cubic ft. of air / 80 cfm fan = 140 minutes to 1 air exchange ,or 2hrs. 20 min. not enough. The 10cfm I said before is for most rooms, code CSA f326 says 20cfm for master bedrooms. National Building Code ref.: 9.32.
Hope this is not TOO much info. Good Luck!
IF IT WAS EASY, EVERYONE COULD DO IT!
Thanks for the replies Guys.
Artworks, did you mean one exchange per hour or one per day? Whew, one per hour seems a lot. Our local building inspector, who is admitedly not an HVAC specialist, suggested I simply connect the fan to the bathroom light switch; the assumption being that if someone were in the bathroom, creating humidity, it would be exhausted. This seems a bit shortsighted to me, as there are many other sources of humidity other than bathroom events.
Scott.
Scott, shortsighted is right. When I built our place 10 yrs ago I followed then Canadian code of .5 ACH, or a total change every 2 hrs. It's been great and guests frequently notice the difference in quality of air between our place and theirs. We filter incoming air and send it through a heat exchanger. Filtering takes out molds, pollens, smoke.
Forget your inspector for advice. For instance, here, an operable window satisfies ventilation requirements. So we have a huge number of unhealthy houses with windows closed at least 6 mo/yr. Older leaky houses obviously fair much better.
Your air system should be part of the overall plan. That's the V in HVAC, but I've met exactly 1 HVAC contractor here who paid any attention. And he said it was due to his daughter's asthma.
We monitor humidity with a simple digital device and turn on a dehumidifier as necessary. Necessary in Virginia means only in summer when it's really humid out. You want 30-50% rh. We rarely see 30% in the winter, usually lower. And we live in a house with no active heating system to dry it out.PAHS Designer/Builder- Bury it!
Thanks All.
Wow, it seems like this is an area in which many people could use some enlightening. My installation involves a basement suite with tenants and I can't count on them keeping a dehumidifier going (many people find them annoying). So I'll go with running the fan either continuously or close to it.
Scott.
Yes, .3 to .5 air changes per hr. WAS the old recommendation., but with all the man made materials inside a home and the growing problems with indoor air quality, they have bunped them up, R2000 ( & model energy code ) sate 23 air changes per day! but it depends on how leaky your building envelope is to know how much mechanical V. to use, Your rihgt to assume that the cleints will not look after a de-humidifier. Try to stop the moisture as close to the source as possible, 1 person will contribue as much as 5imp. gal. of moisture per day. You now know what your up against . Start with the cheapest and go from there . Play with the running of the fan and keep note of what is or is not happening. Watch for moistue sign,s ect. and be vigilant for ANY SIGN'S OF MOLD.
IF IT WHERE EASY, EVERYONE COULD DO IT!
We monitor humidity with a simple digital device
What make is yours and are you satisfied with its accuracy?
I want to get one for our piano.
Edited 3/21/2005 11:49 pm ET by TOMCHARK
We've got a Bionaire, no model number. Grainger used to sell them (~$40) but now has Extech, which presumably is about the same. Monitoring humidity to ensure we don't have mildew growth is our concern and the accuracy seems fine for that. This little unit has needed 2 battery changes in 10 yrs of non-stop operation.
With a piano, I'd also want to use a wood moisture meter to determine what humidity was best for the piano. The one I use is a pinless Wagner that averages mc (moisture content) to 3/4" depth. Don't know a lot about pianos, but generally, wood is happy at almost any mc, as long as it's constant. Once you have it steady, tuning would be in order.
Depending on your climate, I'd try for 50% rh or thereabouts so you don't have mildew worries. When we lived in Denver, nobody I knew ever paid attention and 50% would be very difficult to attain. One client had 2 grand pianos in the corner of her large living room. Don't remember ever checking them, but the rest of the wood in the house was right around 8% mc. Far as I knew the pianos didn't suffer. As they were used whenever the Denver Symphony needed a pair, they got good care.PAHS Designer/Builder- Bury it!
Don't know a lot about pianos, but generally, wood is happy at almost any mc, as long as it's constant.
Well, piano is basically wood. We are trying to maintain RH around 50% year round.
It gets pretty cold here in the winter and with the whole house humidifier we try to maintain the 50%.
If you play piano, a piano is probably one of the best investments. We bought our piano and DW's car about the same time 10 years ago, the car was sold three years ago for 1/3 of what we paid and the piano is just getting into its prime.
I have to check my Canadian Building Code but IIRC it's one exchange every two hours.
To control indoor humidity it depends on the differential between indoor and outdoor humidity and air exchange.
So as Art said in cold climate a HRV should be a consideration especially if you have a tight house.
Just noticed you are in southern BC so depending how leaky your house is you should be fine without a HRV.
If you want to control humidity, get a dehumidifier and hook it to a drain.
I was involved with an indoor swimming pool installation last year. The HVAC company quoted $20,000 for a system. The owners decided to wait for some other prices. The pool guys came, filled the pool, turned on the heaters and pumps and every window in the basement pool area fogged over. I was afraid every door in the living quarters above would swell beyond repair. We bought a decent sized dehumidifier for about $240 and ran the hose into a floor drain. By the next morning, it was noticeably drier and the windows had cleared. We said to #### with the 20 thousand dollar HVAC and mounted the $240 dehumidifier permanently.
A year later and its still working beautifuly.
First, all a fan will do is move air. Fans do not dehumidify. If you are exhausting a point source of moisture (like a shower or a cooking appliance) then exhaust while the source is in use. If the air you move into the space is not dryer than the air you move out, you will not affect the humidity, though the air change will usually improve the air quality. If, as is the case a good portion of the year in your area, you bring in outside air the is very humid, you will be worse off than before. If have a problem with moisture in the basement, the fan will help to mask that problem. Are there any guidelines? No.
There are code requirements for ventilation and exhaust is certain spaces and there are "good practice" guidelines for air changes for general air quality, if applied by a competent designer/installer that has all the necessary info.
More information is needed before any good advice can be provided. How is the exhausted air made up? What is the construction of the building? What is to be the use and what occupation is involved? Etc.
Thanks for the info, Timbo.
My main concern (I think) is Winter when moist air will condense on outside walls (although the vapour barrier is well installed). This house is on a steep slope so the basement is mostly stick framed with a concrete back wall and stepped concrete sides. The entire basement is a two bedroom rental suite. Makeup air is provided with two 5" ducts to the mechanical room which is in the center of the suite. I expect that any negative pressure created by exhaust fans should draw makeup air into the dwelling.
This is a new house, so I have no history to relay. I'm just trying to plan well for the future.
Scott.
Have seen this outfit.http://www.ezbreathe.com/Basically just a bath fan and ductwork for a rediculous price. And they "claim that is dehumidfies" along with curing bad breath and erectile disfunction.Now I don't see a price on this. But I remember a while back some asked about it and I found the price I think about $890.It might have been a company, but similar system.