High CFM range hood.

[nizak]

I have a variable speed range hood (350-800CFM)operating on 120V.

HVAC contractor is requiring 120V power to be sent to a relay in the basement that will operate the furnace blower in turn providing make up air to the kitchen.

120V to the relay can only be on when the blower is operating.

I don’t see how to accomplish this without “getting into” the factory wiring of the hood which will void warranty.

There are 3 push button settings on the console for the blowers if that’s a factor as well in accomplishing what HVAC wants.

Past units I’ve wired have an optional accessory kit from the factory for this application.

Any help appreciated

 

[zbang]

About all I can think of are either a current sensor that activates at the lowest speed/draw or a pressure switch on the output duct (and that seems a bit dodgy).

 

[LarryFine]

Can you use a current sensor in the line to the exhaust fan?

 

[nizak]

Nowhere to put it that I could see. Input cables for both blowers comes from the push button console and are wrapped in a sheathed bundle with the other wiring.

 

[LarryFine]

Nowhere to put it that I could see. Input cables for both blowers comes from the push button console and are wrapped in a sheathed bundle with the other wiring.

I meant in the the line supplying the hood controls.

 

[nizak]

Not following you Larry. One source of 120V power comes into the hood unit . So then the lights probably wouldn’t be enough draw to activate it if they were turned on and the blower wasn’t in use?

 

[zbang]

Get out the ammeter and check? The lights are probably LED and if they top 1 amp I'd be surprised. The fan motor will probably start at a couple more amps and probably wouldn't be used without the lights. Add to that- at low volume, does it even need make-up air?

 

[Barbqranch]

Does the furnace even supply outside air? Mine does not.

 

[zbang]

Some hvac systems do; one of mine takes half outside air and half recirculated, others have dampers to take in and exhaust.

 

[wwhitney]

I was able to use one of these in the panelboard where my vent hood branch circuit originates:

https://www.supplyhouse.com/sh/control/product/~product_id=H608

My range hood has 4 fan speeds and LED lights--the current draw for lights only was less than for low fan speed only, and so I was able to set the pickup to a current level in between. If you need finer granularity or a lower low-end pickup, you can wrap the conductor through the CT window 2 or 3 times; I forget if I had to do that.

Cheers, Wayne

 

[hillbilly1]

Does the furnace even supply outside air? Mine does not.

Maybe an enthalpy damper? Maybe the local energy codes require it, but like you I haven’t seen it done on residential.

 

[Choice_Gorilla]

Last time I did it we used a little CT donut in the wiring compartment for the hood, as others have already stated. Honestly the lights didn’t even cross my mind at the time, a couple little LED MR16s or whatever can’t be more than 30 watts.

 

[Eddie702]

I agree a current sensor is the best choice. They sell them with all kinds of amp ratings. Amp out the lights and blower and select one that will power the furnace when the fans are on but not the lights.

Grainger has an adjustable one with a range of 2-20 amp

 

[kec]

I have a variable speed range hood (350-800CFM)operating on 120V.

HVAC contractor is requiring 120V power to be sent to a relay in the basement that will operate the furnace blower in turn providing make up air to the kitchen.

120V to the relay can only be on when the blower is operating.

I don’t see how to accomplish this without “getting into” the factory wiring of the hood which will void warranty.

There are 3 push button settings on the console for the blowers if that’s a factor as well in accomplishing what HVAC wants.

Past units I’ve wired have an optional accessory kit from the factory for this application.

Any help appreciated

Around here we or the HVAC contractor put a LV sail switch in the exhaust duct back to a relay in the air Air handler to turn on the make -up air.
Very simple.

 

[hillbilly1]

I agree a current sensor is the best choice. They sell them with all kinds of amp ratings. Amp out the lights and blower and select one that will power the furnace when the fans are on but not the lights.

Grainger has an adjustable one with a range of 2-20 amp

That’s what I use.

 

[hillbilly1]

Around here we or the HVAC contractor put a LV sail switch in the exhaust duct back to a relay in the air Air handler to turn on the make -up air.
Very simple.

The problem with sail switches, is they gum up with grease, and get too heavy to operate.

 

[MTW]

An adjustable differential air switch can be used with with two 1/4” tubes placed properly across the fan inlet and outlet.

Used these for years on all types of fans. Just don’t exceed the switch ratings. And install both tubes in the duct pointing towards the fan for proper sensing.

Cleveland Controls Air Sensing Switch, 300 VA Pilot Duty, 3 1/4 in W AFS-222-139 | Zoro

Order Cleveland Controls Air Sensing Switch, 300 VA Pilot Duty, 3 1/4 in W, AFS-222-139 at Zoro.com. Great prices & free shipping on orders over $50 when you sign in or sign up for an account.

www.zoro.com

 

[hillbilly1]

An adjustable differential air switch can be used with with two 1/4” tubes placed properly across the fan inlet and outlet.

Used these for years on all types of fans. Just don’t exceed the switch ratings. And install both tubes in the duct pointing towards the fan for proper sensing.

Cleveland Controls Air Sensing Switch, 300 VA Pilot Duty, 3 1/4 in W AFS-222-139 | Zoro

Order Cleveland Controls Air Sensing Switch, 300 VA Pilot Duty, 3 1/4 in W, AFS-222-139 at Zoro.com. Great prices & free shipping on orders over $50 when you sign in or sign up for an account.

www.zoro.com

I’ve done that with Home Depot’s tool rental rooms, the engineers specified sail switches for fan flow verification, but after a year or so, they would quit working because of dust build up. Replaced every one that failed with a pressure differential switch, and had no more problems.

 

[zbang]

An adjustable differential air switch can be used with with two 1/4” tubes placed properly across the fan inlet and outlet.

I'd be concerned of having them (or anything) on a range hood system and eventually getting yucked-up with oil particles and smoke; those are part of the reason for the hood in the first place.

Is this a dwelling or commercial operation? That's never been mentioned directly.

 

[kwired]

Does the furnace even supply outside air? Mine does not.

Was my first thought. running furnace blower does nothing for Make up air if there is no inlet to bring in fresh air. And that fresh air would be pulled in the inlet whether furnace was blowing or not anyway. If you have high enough volume of air being pulled you may want a fan on the make up inlet as well to help equalize static pressure between interior and exterior though, too much pressure difference can make it difficult to open or close exterior doors or cause back drafting on natural draft type gas appliances.