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Old 01-06-2012, 01:24 AM   #1
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Using a relay to accomplish 3-way switch with 2 single pole?


I have ordered a whole house ventilation fan to draw in some fresh air but mostly to exhaust the humid air from the 2 mold-prone un-ventilated bathrooms in the house. I don't want to run the fan 24/7 and I don't trust the other people I live with to flip a switch when they shower (I've already given up on getting them to turn off lights when not in rooms, motion sensor revenge in their future).

So, I would like to use an adjustable de-humidistat switch, that the manufacturer of the fan sells, in each bathroom. However, these switches are single pole. I have a good deal of home wiring experience (I just ran a 3-way switch set-up for our kitchen lights) but I don't really fully understand relays. I've used them in simple DC automotive applications, but I don't know what to look for in AC, if it even can be done.

I imagine I either need a DPST or DPDT relay but I'm not sure how that works and I don't know how I would hook up the connections from the two switches to the relay.

According to the website, the switches can operate using 24v or 120v. I'd prefer a relay that switches using 120v feeds so I don't have to get a 24v transformer for the switches.

Please advise which relay can accomplish this and how to hook it up.

Thanks,
Doug

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Old 01-06-2012, 01:49 AM   #2
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Using a relay to accomplish 3-way switch with 2 single pole?


Just wire the de-humidistat switches in "parallel", then no relay needed.

This would be like 2 regular light switches connected in parallel....

Top screw..................Top screw.......wire to light
[Switch 1] __________[Switch 2]
Bottom screw.............Bottom screw...wire to light

Then either switch on, light on.
Both switches must be off for light to be off.

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Old 01-06-2012, 02:45 AM   #3
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Using a relay to accomplish 3-way switch with 2 single pole?


Humidistat is the best option, with remote fan with ducting going to each bath. Why reinvent the wheel. Same for wiring some funky/wonky switch setup.
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Old 01-06-2012, 05:08 AM   #4
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Using a relay to accomplish 3-way switch with 2 single pole?


I concure with both Billy and Greg.....

A lot simpler than you thought...right?
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Old 01-06-2012, 05:31 AM   #5
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Using a relay to accomplish 3-way switch with 2 single pole?


I have always had whole house fans and I just love them. However, I want to bring up a point that may pertain to your application. To move air, you need to exchange the air. Meaning your bathrooms will need to have a window or some means of introducing fresh air into the room. Not knowing where you live but do you think the family members would open an outside window while showering in the winter? I don't think so, and neither would I. Is there any way to add conventional exhaust fans? I think that is your only option here.

Edit: Your post made me think about something that happened with my whole house fan. When I was building my house one of the sinks in a bathroom hadn't been installed yet so the waste pipe was just sticking out of the wall. I went into the bathroom and was almost knocked over from the smell of sewer. I was running my whole house fan but I didn't have enough windows open so it was sucking sewer gas right through the waste pipe. A temporary blind cap solved that problem real quick.

Last edited by zappa; 01-06-2012 at 05:59 AM.
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Old 01-06-2012, 06:55 AM   #6
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Using a relay to accomplish 3-way switch with 2 single pole?


zappa, that is why you either duct tape, or glue a cap on the stub, with enough extra sticking out of the wall, so that you have a finished length, when you cut the cap off. I just tape the end, some people stuff a rag into the hole.
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Old 01-06-2012, 06:55 AM   #7
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Using a relay to accomplish 3-way switch with 2 single pole?


Quote:
Originally Posted by Billy_Bob View Post
Just wire the de-humidistat switches in "parallel", then no relay needed.

Then either switch on, light on.
Both switches must be off for light to be off.
Correct. This situation does not need a real three way.

Here there is neither the need nor desire to let the manual switch force off the fan by being flipped the other way.
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Originally Posted by gregzoll View Post
I just tape the end, some people stuff a rag into the hole.
A rag would have to be large enough to be packed in tight to withstand suction from the whole house fan.
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Last edited by AllanJ; 01-06-2012 at 06:58 AM.
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Old 01-06-2012, 08:22 AM   #8
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Using a relay to accomplish 3-way switch with 2 single pole?


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Originally Posted by gregzoll View Post
zappa, that is why you either duct tape, or glue a cap on the stub, with enough extra sticking out of the wall, so that you have a finished length, when you cut the cap off. I just tape the end, some people stuff a rag into the hole.
Thanks gregzoll.....it wasn't too big of an issue. A short piece of pipe and a blind cap, no glue necessary. PVC usually has a pretty tight fit with no glue applied and it stayed on just fine in my case.
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Old 01-06-2012, 09:27 AM   #9
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Using a relay to accomplish 3-way switch with 2 single pole?


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Correct. This situation does not need a real three way.

Here there is neither the need nor desire to let the manual switch force off the fan by being flipped the other way.
. Thank you. I wasn't grasping why this situation would be different than a 3-way switch. Yes I want the fan to keep running if either de-humidistat is on. No need to force it off. I hope the fan helps clear the air of my brain fart on this one.
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Old 01-06-2012, 10:37 AM   #10
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Using a relay to accomplish 3-way switch with 2 single pole?


Quote:
Originally Posted by zappa View Post
I have always had whole house fans and I just love them. However, I want to bring up a point that may pertain to your application. To move air, you need to exchange the air. Meaning your bathrooms will need to have a window or some means of introducing fresh air into the room. Not knowing where you live but do you think the family members would open an outside window while showering in the winter? I don't think so, and neither would I. Is there any way to add conventional exhaust fans? I think that is your only option here.
The "whole house ventilator" I'm installing is more of a conventional bathroom exhaust fan than what I consider a whole house fan.
Here's the product web page:
http://www.broan.com/display/router.asp?ProductID=549

It has four 4" intake ports and one 6" exhaust port. It's like having a bathroom fan with the actual fan downstream in the duct. The real advantage is that I take care of 2 bathroom's with one fan and one exhaust damper/cap. Additionally, I'm hoping to improve the indoor air quality which has been an issue since we moved in 2 years ago.

I will use 2 of the ports for the bathrooms and a third for the center hallway. Then my HVAC installing brother-in-law is going to help me figure out how much fresh air intake I'll need to deal with pos/neg air pressure when things like the stove hood and furnace blower are on. The house was built in '38 and is far from air tight, but I do live in New England and if enough air intake is necessary I will probably go with a energy recovery ventilator.

I know it seems overkill. But I have been waging a constant war with mold in this house and I worry about the health of my young children. When we first moved in I discovered both bathrooms plumbing had small leaks for long enough that I had to tear down 10'x15' sections of the basement ceiling underneath each one to get to all the visible mold.

Then when the leaky roof forced me to gut one of the upstairs bedrooms I found that there was absolutely no ventilation in the attic crawl spaces or for the roof (the continuous eave vent material is purely cosmetic).
It was a attic turned into living space situation (I won't go into all the structural issues, I'll just say that replacing the ridge beam was one of many necessary projects) and the windows at the gable ends used to be large louvered vents that provided the only ventilation. This lead to horrible amounts of condensation on the underside of the roof sheathing and, you guessed it, more mold. The bathrooms not having exhaust fans added to this problem by ensuring all humidity stayed in the house. At the time of the roof leak last winter, the average humidity level upstairs during a dry winter day was about 65%!

I already installed a ridge vent when we replaced the roof this Summer. Then I spent a lot of time on a ladder installing over 100 circle vents in the eave overhangs. I'm extensively using plastic vapor barrier to separate the attic crawl spaces from the living space of the house. So, far there is no evidence of any more condensation issues on the roof sheathing this winter. And, God willing, this house ventilator will take care of any other moisture issues from the bathrooms.

On top of all this, I've replaced about 1/3 of the plumbing and 1/2 the wiring in the house. I now watch "The Money Pit" with a new appreciation. AHH, HOME CRAP HOME!
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Old 01-06-2012, 11:03 AM   #11
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Using a relay to accomplish 3-way switch with 2 single pole?


Quote:
Originally Posted by sissond View Post
The "whole house ventilator" I'm installing is more of a conventional bathroom exhaust fan than what I consider a whole house fan.
Here's the product web page:
http://www.broan.com/display/router.asp?ProductID=549
Nice unit.....quiet too I'll bet. Sorry to make you do all of that typing but it was an interesting read.
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Old 01-06-2012, 01:45 PM   #12
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Using a relay to accomplish 3-way switch with 2 single pole?


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Nice unit.....quiet too I'll bet. Sorry to make you do all of that typing but it was an interesting read.
Yes, supposedly it does 210 CFM at 2.0 sones. I got one of their RP series hoods for my kitchen when we first moved in. It is listed at 0.5 sones on low and it is indeed whisper quiet on low. It also does a great job handling normal levels of steam at that speed. I rarely have to turn it to high unless I'm using 3-4 burners.

I didn't mind all the typing. I occasionally need an outlet to vent some of my frustrations with this house. My wife says I sound like an episode of Holmes on Homes when I really get going.
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Old 01-06-2012, 05:43 PM   #13
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Using a relay to accomplish 3-way switch with 2 single pole?


You could use a SPDT relay with 120v coil,
You just wire the set up like a 3 way switch,
But the relay replaces one of the switchs.

This would be the most flexable option !

You could also use A DPDT relay,
so long as it has 2 throws.
It doesnt matter how many poles.

You would have to use a deep box to hide the relay !
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Old 01-06-2012, 05:45 PM   #14
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Using a relay to accomplish 3-way switch with 2 single pole?


Quote:
Originally Posted by dmxtothemax View Post
You could use a SPDT relay with 120v coil,
You just wire the set up like a 3 way switch,
But the relay replaces one of the switchs.

This would be the most flexable option !

You could also use A DPDT relay,
so long as it has 2 throws.
It doesnt matter how many poles.

You would have to use a deep box to hide the relay !
Mate....I guess you didn't read all the posts........

No relay needed....problem was already solved.

Quote:
Originally Posted by Billy_Bob View Post
Just wire the de-humidistat switches in "parallel", then no relay needed.

This would be like 2 regular light switches connected in parallel....

Top screw..................Top screw.......wire to light
[Switch 1] __________[Switch 2]
Bottom screw.............Bottom screw...wire to light

Then either switch on, light on.
Both switches must be off for light to be off.

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