Four bathrooms & one central fan: AC relay?

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Old 12-29-07, 07:31 PM
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Four bathrooms & one central fan: AC relay?

Hey guys, new here.

I am renovating an old house with four bathrooms. I decided to go with one central exhaust fan mounted in the attic to serve all bathrooms at once.

I want to put timer switches into each bathroom, but I'm not sure how to control the single fan with four timer switches. From my days in another life as a car alarm technician I was proficient in using DC Bosch-style relays to get an alarm to control just about anything... and I'm thinking that something along those lines, but for AC, will work here.

So basically I have a 110V up at the fan in the attic, then I am running a circuit down to each bathroom. What would be the best way to turn on the fan when any single circuit is completed?
 
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Old 12-29-07, 07:36 PM
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You could use a couple of little $8 ice cube relays and plugin bases to accomplish this.
 
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Old 12-29-07, 07:38 PM
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Not sure how you will accomplish this, not only from a switch standpoint (you can use low voltage control modules) but from a volume standpoint. Your trunk line will have to be no less than 10" in diameter to handle the potential of all the fans running at the same time. Believe me, it would be easier to run flex from each fan up a wall cavity and exit out the soffit.
 
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Old 12-29-07, 08:06 PM
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Originally Posted by dezwit View Post
You could use a couple of little $8 ice cube relays and plugin bases to accomplish this.
Are those something that I can get at Lowes? I'm assuming that they work similar to the DC equivalent that are used on cars, yes?


Originally Posted by chandler View Post
Not sure how you will accomplish this, not only from a switch standpoint (you can use low voltage control modules) but from a volume standpoint. Your trunk line will have to be no less than 10" in diameter to handle the potential of all the fans running at the same time. Believe me, it would be easier to run flex from each fan up a wall cavity and exit out the soffit.
The exhaust is dumping into the no-longer-used chimney which is plenty large enough to carry the volume. That was a good point to anyone else considering this, though.
 
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Old 12-29-07, 08:14 PM
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Just put a switch in each bathroom and wire them all in parallel. This way any of the switches can be used to turn the fan on.

No need for anything low voltage or exotic.
 
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Old 12-29-07, 10:22 PM
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I agree with Bob. No need for anything special. This project is simple as dirt. Keep it that way.
 
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Old 12-30-07, 01:48 PM
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Oh yeah... maybe I was trying too hard! My brain still thinks in DC sometimes, so I miss the obvious solution. I'll let you know how it goes!
 
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Old 01-01-08, 07:02 AM
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I like working with controls to make life easier.

I would go with four push buttons and a time delay relay.

Of coarse you can start with the switches and if you find it is a pain to go to four bathrooms to shut the fans off, you can change the relay system easy later.
 
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Old 01-01-08, 04:14 PM
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I like the idea of a central fan, much quieter. Bathroom fans can easily suck the heated air out of your house, especially if you have the capacity of 4 of them. Good luck with the switches.
 
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Old 01-01-08, 04:48 PM
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Originally Posted by jwhite View Post
I like working with controls to make life easier.

I would go with four push buttons and a time delay relay.

Of coarse you can start with the switches and if you find it is a pain to go to four bathrooms to shut the fans off, you can change the relay system easy later.
so what happens if 1 person is using each of the restrooms and the first guy to leave is conscientous and shuts the fan off??

Parallel timer switches woudl eliminate that situation.
 
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Old 01-01-08, 05:24 PM
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Just a couple of thoughts on a few issues with your plan.

If you were to have four switches in parallel controlling a single fan and you have multiple people using these bathrooms you will likely find yourself searching for a single switch if someone does not turn it off.
If you wanted to use a timer a simple 120 volt mechanical timer in parallel would eliminate any complexity and save searching for where to turn off the fan.

You will need a fan that has four times the normal capacity to serve four bathrooms which is very inefficient as far as venting heated air in the winter and cooled air in the summer if you have a/c.
It is common here in our cold climate for larger homes to have a single fan to exhaust multiple rooms but it is done through an air/air heat exchanger to maximize efficiency.

Venting exhaust air through a chimney can cause condensation to form in cold weather which could damage the brickwork.
Also, if the back draft damper at the fan were to leak, in cold weather you could have cold air dropping down the chimney cooling off the bathrooms.
 
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Old 01-03-08, 11:15 AM
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4 baths, 1 fan

This is basically the same setup I've considered.
But I haven't figured out how to prevent the central fan from sucking air from ALL the baths, no matter which switch is on.
Flopping dampers won't work.
Any other ideas?
Thanks.
 
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Old 01-03-08, 01:12 PM
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I'm just going with all bathrooms at once... I opted for the larger fan that can handle the volume... it is kind of an experiment since I'm selling the house when I am done.
 
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Old 01-03-08, 04:38 PM
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Originally Posted by DarrenDriven View Post
it is kind of an experiment since I'm selling the house when I am done.
Former homeowners experimented in my house. After seven years, I'm still finding things ...

Not trying to be snide here, but why don't you just install four fans?
 
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Old 01-03-08, 07:52 PM
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Hehe... well, I must be honest that I haven't really decided to sell once the house is done... it might NEVER be done, and maybe someday if it is done I won't want to get rid of it.

That being said, I figured that it was a little more high end to install a four-room system with a nearly silent fan. I don't have to cut through the outside wall for each bathroom. (I just finished residing and painting the entire house) Plus, the fan that I purchased is purpose-built just for this application.

The installation of the exhaust system isn't as much an experiment as the wiring controls... but now that I realized that I can just wire the fan in parallel without anything fancy it isn't even that much of an experiment.

This is an eighty-year old, 3000sf house that has undergone a couple of remodels in the past 30 years that have virtually ruined the place. I have been renovating it back to (or greater than) its original condition. I am taking a few design liberties that are a little more daring than a true restoration, but nothing too crazy.


BEFORE



AFTER
 
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Old 01-03-08, 09:22 PM
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Wow! I love the result. Amazing transformation. Congratulations!
 
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Old 01-03-08, 11:58 PM
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yes, it does look very good.

You can add a bit it you want by adding power dampers, 1 to each of the 4 runs. That way you would only draw from the room that has the energized switch. It will take a bit more work but it is possible.

One downside, the fan is presumably sized for all 4 rooms. If you use it to evac just one room, obviously it will suck the occupant up to the ceiling and suck theire hair off.

So, if youwant to consider power dampers, let us know. There are multiple ways to do this and I am sure with the guys we have here, there will be several good methods to achieve the result.

I would still want to leave the 4 timer switches so each room could turn on the fan and as the timer expired, the fan would turn off if no call from the other rooms yet nobody could turn the fan off if any other switch called for the fan.
 
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Old 01-04-08, 05:01 AM
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Wow. (crunch-crunch) That's the sound of me eating my words. If you have any spare time, can you come over to my house to experiment?

Please consider posting your project on the Did It Myself section of this site.

If the venting can be worked out and you don't want to use a timer, consider putting the fan on the light switches. It's more likely that people will remember to turn off the lights when they leave a room.

In that case each light switch would control the light and the coil of an AC relay. The switched sides of the four relays would be wired in parallel to the fan to isolate each switch leg from back-feeding to the others. (This would also be the arrangement you'd need to use powered dampers.)
 
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Old 01-04-08, 10:14 AM
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Hehe, thanks for the compliment, I'll add my house to the section soon.

I am going to go with timers for a couple of reasons. It is a simpler and more elegant solution, and it will allow people to "set and forget" when they leave the room instead of leaving the light on and walking away.

I'll post a progress update soon.
 
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Old 01-04-08, 10:24 AM
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Current thinking (as I read it from various sources) is that you should run the fan in the bathroom for 20 minutes following a shower, to allow the fan time to remove the humid air. This is much easier done with a timer than with a switch, especially if the switch is tied to the lights.
 
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Old 11-05-08, 08:39 PM
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Hey guys, I'm back. I took some time off this summer to goof off and I am just now finishing the final details of the entire upstairs remodel in the house.

I'm back to my original question, though. Each bathroom will have one timer switch. That switch will control the light and the fan -- I didn't really think about this when the idea to wire the switches for each bathroom in parallel. If the switches were controlling ONLY the fan then it wouldn't be a problem, but since there are lights wired to each switch then one switch turned on would turn on the light in every bathroom. This means I need some kind of device to prevent backfeeding juice from the fan to the other circuits.

So in the attic at the fan I will have four hot wires. I need some kind of relay device that will let any hot wire turn on the fan but won't let that power head back down any of the other three wires.

In a car I could use some $5 Bosch relays to do this, but I have no idea how to do it using AC. Someone please help!
 
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Old 11-06-08, 03:47 AM
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How can this be possible to connect?
Using only two conductors from each location is not enough.
Considering the lovely job you did on the house why is it not possible to retrofit another 120 volt cable and switch to each room or use your DC experience and install some low voltage wiring and a relay to control the fan?
 
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Old 11-06-08, 05:22 AM
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Low voltage, as suggested a year ago, and again by Greg. Simple to use, and since you already have DC experience, you can do it. You won't do it using line voltage without running more cable to each location.
 
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Old 11-06-08, 09:52 AM
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Well, I already have the cables running to each location and the switches and lights installed, so to redo it with low voltage would probably be a hassle at this point.

In the attic at the fan I have four cables, one from each bathroom. At this point only one is hooked up (master bath) so that when I turn on the master bath light the fan comes on. In the other three bathrooms you can turn the light on, but the fan doesn't come on because I don't have the wires hooked up. I could hook everything up in the attic, but like I mentioned before, the lights would come on in ALL bathrooms when one is turned on, so I have not hooked them up yet.

I guess what I am looking for is an AC-triggered relay or switch, that can isolate each individual bathroom circuit but still turn on the fan. It seems simple enough to me, but I just haven't been able to find it yet.

Hoping that someone out there has the answer!
 
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Old 11-06-08, 10:50 AM
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Maybe you can get creative with something like wireless or X-10 because you ain't going to make any magic operating two devices in four locations with only two conductors from each location.
 
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Old 11-06-08, 11:06 AM
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I'm sorry, maybe I didn't explain this properly. I have a cable running from the light circuit in each bathroom to the fan in the attic. So that makes four cables arriving at the fan. (when I say cable I mean a regular three-wire power cable containing hot, common and ground wires)

I don't need to send any power back to each bathroom at all... the ducting for the single fan is already in place so I simply need to turn the fan on.

Now if I hook all of the wires together (series or parallel) then what will happen is that when the switch for one bathroom is turned on the fan will work as desired, only the lights for every bathroom will also turn on. (not to mention that is scary because you have power from totally different circuits feeding into other circuits)

So I am simply looking for some kind of device or method that will allow any single hot line to turn the fan on, but will not allow the electricity to backfeed into the three other lines.

There is power at the fan that is on it's own utility circuit that I can use, so I really only need the AC power from each bathroom to trigger some kind of switch or pass through some kind of non-backfeeding-device (like a diode in DC speak).

I'm sure that there must be a relay that can be triggered by an AC signal, I just don't know what it might be called or where I might be able to get it. That is ultimately what I am hoping that someone here will be able to tell me.
 
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Old 11-06-08, 03:04 PM
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I'm sure that there must be a relay that can be triggered by an AC signal, I just don't know what it might be called or where I might be able to get it
Yes. It's called a relay.

actually, you need 4 of them but you also need a full time hot at the fan (or where the relays will be actually)

Each of the switchlegs you have coming to this area will operate a seperate relay that controls a hot circuit that then powers the fan. Use the same hot circuit to feed through each relay for the fan.

So, what will happen is if you turn on light in room #1, it will turn on that light and it will energize a relay. THat relay controls power for the fan.'

Do this with each switchleg using seperate relays for each switchleg.

what is the power requirements for the fan? If it is quite low, you could use "ice cube relays". If it draws a lot, you would just use a higher capacity relay.

edit:
just went back and re-read your last post. It seems you do have a seperate power circuit up there for the fan already.

You're good to go them.

Put the relays in a junction box. You can get them anywhere from 4"X4"X4" to (nearly litterally) as large as you want.
 
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Old 11-06-08, 03:09 PM
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This is exactly what I figured I could do, I just wanted to make sure that it was possible.

Are these relays something I can get at Lowes or Home Depot? I walked down their electrical aisle and didn't see anything... can you maybe find me a photo or a link to some kind of example so I can go out and find some of these local to me? Thank you! Thank you!
 
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Old 11-06-08, 03:28 PM
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what's the current draw of the fan?

here is a page that has a multitude of relays. any of them with the proper coil voltage (120 volts) would work.

http://images.google.com/imgres?imgu...IH:en%26sa%3DN

I typically use the style of the last 3.

Make sure the relay is rated to handle the current draw as well as the inductive load.

If you need something bigger, there a myriad styles of relays available.
 
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Old 11-06-08, 04:44 PM
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Thanks nap! They remind me a lot of the DC relays that I used in car security... this should hopefully be a snap now! I'll update the topic when i get things rolling.
 
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Old 11-10-08, 01:56 PM
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Your system sounds interesting from a tinkerer's point of view. But, I think it would be wasteful from a practical point of view. You must not have teenagers, they will leave lights and fans on all night or all day. Even wives don't have much concern for this type of thing. I don't like the light and fan to be tied together either. I found in the winter it is nice to run the furnace fan continously from 6-8 in the morning (w/ a prog therm.) when everyone is showering and you don't need a fan. You get the benefit of all that warm moist air instead of wasting all the climate controlled air. I like the idea of remote individual fans, so you get the quiet fan without running all the fans at once.

Good luck and keep tinkering.
 
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Old 11-11-08, 02:18 AM
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Chris,

Hehehe... no, I don't have teenagers, but I did think ahead. Every bathroom has a timer switch instead of a regular light switch. That pretty much eliminates the wastefulness of lights and fans left on.

I personally don't like the fan and light together, which is why the master bath is the only one that has separate light and fan controls. The other three baths are going to be for guests, roommates or maybe kids. By tying the fan and light together I will insure proper ventilation for both humid shower air and toxic toilet-related air. It might not be the ideal solution for everyone, but since I have roommates right now that are kind of lazy I think that I will like it this way.

There were a couple of other reasons that I didn't put individual fans in each bathroom, but ultimately I could have done it if I really wanted to. I think that when I sell the house the idea of one very quiet, powerful central fan will be perceived as a higher-end detail that might set my house apart from many others.
 
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Old 11-13-08, 12:03 AM
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OK, we have success. I stopped by an electrical supply store and picked up four Eaton D3PF2AA DPDT relays along with four base plates. The relays were $11.66 and the plates were $3.57.

I didn't really need DPDT relays, SPST would have worked fine, but the store didn't have the Single Poles so I went with the Doubles.

I used the pair of wires from each bathroom to trigger each relay, and wired the dedicated fan circuit through each relay to power the fan. It works exactly as I expected and I can knock this project from my list.
 
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Old 11-13-08, 02:09 AM
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that type of relay does not come in a sp, only a dp. Sorry about not saying something about that.

since you tinker, just so you know, they also make a 3pdt in a similar style but it uses a 12 pin base instead of 8 pin.

glad to hear it works for you.
 
 

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