Relay controlled fans from furnace

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purduephotog

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Rochester, NY, USA
I have a number of booster fans I need to turn on and off from the furnace. My original thought was to use the aux 24v relay in the furnace to switch a second circuit (load would be about 400w).

This would require running 14/2 everywhere.

Would an alternative be too running control wire with a switched relay at each point?

I tried searching for code or best practices on this and came up blank, which just means I didn't look out use the right terms.

If you can point me to the right area I think I can go from there.

Thank you.

Jason
 
boosting fans that do what exactly? forced air HVAC system?

depending on how you will reach each fan with 120v, i might suggest you use a single SSR to switch the hot leg of the ckt, this saves having to run control wire to each fan, and, SSR is more reliable than coil/contact relay.
 
ptonsparky said:
You wil have to run power to each fan. "14/2 everywhere".

One RIB, at one location to control all the fans. Why would you want to have more than one RIB?
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exactly.

the rib seems to be the easiest way to go. but get the SSR version. if the fans are boosters for moving hvac air then the timer option is better, you let the fans run ~30-60sec after demand for heat/cooling is over, this helps get the heated/cooled air in the ducts out into the room. not required if your thermostat already has this feature, etc.


Solid State (RIB) Control Packages by mars
 
FionaZuppa said:
exactly.

the rib seems to be the easiest way to go. but get the SSR version. if the fans are boosters for moving hvac air then the timer option is better, you let the fans run ~30-60sec after demand for heat/cooling is over, this helps get the heated/cooled air in the ducts out into the room. not required if your thermostat already has this feature, etc.


Solid State (RIB) Control Packages by mars
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400W is not very much. If the aux relay in the furnace has a set of dry contacts and rated for the fan voltage, an additional relay may not be required.
 
FionaZuppa said:
boosting fans that do what exactly? forced air HVAC system?

depending on how you will reach each fan with 120v, i might suggest you use a single SSR to switch the hot leg of the ckt, this saves having to run control wire to each fan, and, SSR is more reliable than coil/contact relay.
Click to expand...

Valid suggestions; however they don't address the OP's requisites (criteria).


The post indicates multiple fans that needed to be controlled independently-- perhaps even outside control of the furnace itself—although the fans have to work in conjunction with the furnace.


The 24 VAC control circuit can be utilized to drive the relay/s. Since you are concerned about running #14 conductors, you can run low voltage signal wires class II by using Cat 5/e plenum type because of possible exposure to high temps. (see Article 725-40)


It doesn't matter whether this is for HVAC or centralized heat source for drying and /or climate control, the choice between solid state or electro-mechanical relay is not important. SSR is just an added bonus.
As one poster says you still need to control those relays.


Your second 400-watt circuit (as you indicated) is outside the control circuit loading. If you have concerns about adding load to existing control circuit, it would not be a big expense by adding a step down 24vac transformer similar to annunciator or door bell.
 
myspark said:
Valid suggestions; however they don't address the OP's requisites (criteria).

The post indicates multiple fans that needed to be controlled independently-- perhaps even outside control of the furnace itself—although the fans have to work in conjunction with the furnace.
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hmmm, well, i did not read independent control of each fan, not sure why you did.

independent controls requires a relay attached to furnace 24vac, distributed to low-V toggles in walls (or wherever), and a relay on each fan. 120vac has to be pulled to each fan no matter what.

but from what the OP posted, sounds to me like all the other posts. relay the fans ckt right there at the furnace.

and dam straight it matters what the fans are used for. in many many cases for varying reasons one would never choose to use a coil-contacts based relay !! sure, it now seems like the OP is boosting HVAC air, so a coil relay is ok, but for about the same price these days why not choose the better SSR ???
 
FionaZuppa said:
hmmm, well, i did not read independent control of each fan, not sure why you did.

independent controls requires a relay attached to furnace 24vac, distributed to low-V toggles in walls (or wherever), and a relay on each fan. 120vac has to be pulled to each fan no matter what.

but from what the OP posted, sounds to me like all the other posts. relay the fans ckt right there at the furnace.

and dam straight it matters what the fans are used for. in many many cases for varying reasons one would never choose to use a coil-contacts based relay !! sure, it now seems like the OP is boosting HVAC air, so a coil relay is ok, but for about the same price these days why not choose the better SSR ???
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Perhaps OP needs to come back and clarify what exactly his intentions are. . . instead of going through all these hypotheses.
Not all SSRs are the panacea of all issues that are present in control circuits.

They are sensitive to high temps unlike those time proven electro-mechanical relays that don't require heat sinks.

I've wired giant forging furnaces and the work area is constantly around 103 F, 24/7.
 
myspark said:
Perhaps OP needs to come back and clarify what exactly his intentions are. . . instead of going through all these hypotheses.
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perhaps

myspark said:
Not all SSRs are the panacea of all issues that are present in control circuits.
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true

myspark said:
They are sensitive to high temps unlike those time proven electro-mechanical relays that don't require heat sinks.
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not sure, i find many of the Omron SSR's rated at operating temp of 80C (176F). mechanical are subject to bad contacts, dirt, noise generation, slow rise/fall times, sticking contacts, etc etc.

myspark said:
I've wired giant forging furnaces and the work area is constantly around 103 F, 24/7.
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how big was the furnace? i find many of the Omron SSR's rated at operating temp of 80C (176F). but i suspect by theorized hypothesis that the OP does not have a operational high-temp problem to design around, but we should ask. in general, SSR's are preferred.
 
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How far you need to run, what is acessible, how easy it is to tie back to the furnace (120 or 24 volts) all impact what may be easiest way to do it. If these are at the end of a long main duct and is difficult to get back to furnace - maybe even use a pressure switch to sense increase in static pressure in the duct to start your fans. If your booster fans drop the static pressure too much, that won't work - they will just cycle on/off as pressure keeps cycling - but if you encounter that you have serious ducting issues and boosters probably aren't the answer either.
 
ptonsparky said:
IMO, Boosters are the result of poor design to begin with.
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where's the admins here to close you down? poor design has nothing to do with the OP's question :lol:

and, OP only said "booster fans", but we really have no idea if its actually boosting anything, or its just the name of the type of fan being used. i have also seen "booster" fans used to suck hot air from top of cathedral ceiling and move it to another room(s). ceiling fans dont always work when, as example, such room has a hefty wood burning fireplace and this room gets way to hot, so you use "booster" fan (aka inline) to move that heated air around as needed.

we dont know why such fans are being used, but i think OP has enough info to make an informed decision on what to do.
 
FionaZuppa said:
where's the admins here to close you down? poor design has nothing to do with the OP's question :lol:

and, OP only said "booster fans", but we really have no idea if its actually boosting anything, or its just the name of the type of fan being used. i have also seen "booster" fans used to suck hot air from top of cathedral ceiling and move it to another room(s). ceiling fans dont always work when, as example, such room has a hefty wood burning fireplace and this room gets way to hot, so you use "booster" fan (aka inline) to move that heated air around as needed.

we dont know why such fans are being used, but i think OP has enough info to make an informed decision on what to do.
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OP's mentioning of somehow tying them to the furnace is a big indication that they likely are boosting the air being delivered by said furnace though.
 
kwired said:
OP's mentioning of somehow tying them to the furnace is a big indication that they likely are boosting the air being delivered by said furnace though.
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as the saying goes, which is a 50/50 conundrum ;)

perhaps yes, and perhaps no, we suspect yes, but we dont know

tying to the furnace relay only tells me the fans are used to move air when furnace is on, perhaps just to move air from one high ceiling into a more distant add-on room. i dunno.
 
Thank you all.

I have a problem of designing things overly complicated. The independent control of the fans was to deal with rooms that get too warm and too cool, I wanted to better regulate.

I also have an issue with too little make-up air that I needed to address, so if I made my controller (down the road) cognizant of pressure drop I could shut of the fans drawing the most air away from the basement.

In the summer and winter I could boost different areas depending on what needed it.

I really would have had no issues running 14/2 everywhere... At least the price had come down some. I also know how expensive ssr and relays are so as a cost saving measure it doesn't make much sense.

When I get some sleep I'll respond to the points individually.

Without adding a complication now there's also a small laser cutter with a huge impeller for smoke collection and exhaust. I can't run it until I deal with the duct issues and safely push that outside. But pressurized the house with make-up air when it's running isn't behind the possibilities.

Thank you all again for the excellent ideas and viewpoints.
 
Excuse my ignorance but having never used a relay in a box I'm guessing there is not a need to install a barrier between the high and low voltages? Does that only apply to switches?
 
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