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Thread: Relay controlled fans from furnace

  1. #1
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    Relay controlled fans from furnace

    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

  2. #2
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    Appleton, Wi
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    Just use a RIB (relay in a box) at each fan and 24V control to each RIB.

    https://www.amazon.com/Functional-De.../dp/B01L2MOI48

  3. #3
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    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.

  4. #4
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    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?
    Tom
    TBLO

  5. #5
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    I'm thinking same as pton'...

    Don't you have to run 14/2 to each fan anyway?
    I will have achieved my life's goal if I die with a smile on my face.

  6. #6
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    Quote Originally Posted by ptonsparky View Post
    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?
    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

  7. #7
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    Quote Originally Posted by FionaZuppa View Post
    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
    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.
    I will have achieved my life's goal if I die with a smile on my face.

  8. #8
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    Quote Originally Posted by FionaZuppa View Post
    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.
    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.

  9. #9
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    Quote Originally Posted by myspark View Post
    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.
    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 ???

  10. #10
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    Quote Originally Posted by FionaZuppa View Post
    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 ???
    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.

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