We recently installed a kitchen island and for various reasons there are no acceptable places to put a vent switch close at hand.

I would like to make the whole system more automatic and link the vent to gas flow. (with an additional manual switch in a less convenient location)

I'm having trouble finding an appropriate device that could switch on my vent fan when the smallest single burner on the stove is running.

So far I'm looking at something like this: https://www.alliedelec.com/product/dwyer-instruments/v6epb-b-s-1-b/70408848/

But I'm not sure if it's appropriate. It seems to be intended for things like detecting if a boiler is running, and this use should be very similar, but my minimum flow may be smaller.

Has anyone ever heard of such a construct? Is there a purpose built product I'm missing?

  • Your vent doesn't have a switch? Why would you want the exhaust fan on everytime you turn a burner on? – Gunner Nov 20 '19 at 18:42
  • it doesn't have a switch yet, because I haven't installed it yet. ; ) (in truth there's a temporary switch sitting in a metal box on the floor at the moment) And I want the exhaust fan on every time we turn a burner on to prevent accumulation of CO or Natural gas in my home. Isn't that what the vent is for? – aaronP Nov 20 '19 at 18:46
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    FWIW mine seems to be manual as well. I suspect the knob is connected to a mechanical valve. The ignitor just fires when you turn the knob past the light setting.. but there's no smarts there. It'll stop trying and just dump gas into the room if you turn the knob fast enough. – aaronP Nov 20 '19 at 19:30
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    use a remote control switch with a hard-wired base unit and a battery-operated (or self-powered) remote control that you can place anywhere. A smart switch/outlet would work as well. You can also use an IR flame sensor if you want it automated. – dandavis Nov 20 '19 at 20:24
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    Just going to leave this here to see if it sparks your interest: flame sensor – JPhi1618 Nov 20 '19 at 21:10

The switch linked in the question (Dwyer model V6EPB-B-S-1-B) won't work because its actuation requirements are too high. From its data sheet, actuation-deactuation flow rates for air in SCFM for the 1/2" pipe size valve are 6.50/5.00. (I'm presuming that they'll be similar for a non-air gas, ie fuel gas.)

An article at hunker.com asserts that "In most cases, all burners on the stove adjust down to about 1,000 BTUs" but also states "a low flame on the stove may only use 400 BTUs even though the burner might have an 18,000 BTU capacity." That's a little inconsistent but it's a place to start. There's no time unit specified but typically Btu is per hour.

The FAQs at eia.gov indicate that "In 2018, the U.S. annual average heat content of natural gas for the residential, commercial, industrial, and transportation sectors was about 1,036 Btu per cubic foot."

Combining these typical numbers, we estimate that a large gas burner of 18,000 Btu/hr will result in a flow of 18000/1036/60 = 0.29 cubic feet per minute. That's significantly below the V6EPB-B-S-1-B thresholds. The low-flow model V6EPB-B-S-LF actuates as low as 0.18, so it could detect the burner at high flow, but it wouldn't stand a chance if the burner were turned down to 400 Btu/hr.

Perhaps you could consider sensing something else such as heat or light from the flame. Or latch the fan on automatically when the gas igniter is energized, and use the more distant switch to turn the fan off when it is no longer wanted.

  • Thanks! That helps a lot for figuring out the feasibility of this thing. – aaronP Nov 20 '19 at 19:48

This is generally more of a commercial requirement/product. I am not 100% sure of the details, but in my synagogue's kitchen there is a switch that needs to be turned on to turn on the fans in order to be able to use the gas stove - i.e., without that switch on, you can't turn on the gas. But that doesn't really help you because if you could install such a switch, you could just use it to turn on the fan separately from the gas.

I would also be concerned because a really good exhaust fan (actually, even most of the more basic ones) has multiple speeds - e.g., low/med/high or a variable range. If you can't even mount an on/off switch, that means always turning the fan on at one speed, which will likely be too strong & noisy for some uses and not as strong as you'd like for others.

Back to the specific product: Yes, something like that could work. However, if you are connecting directly to 120V power then you have some serious safety & code issues. Better, but not trivial, is to use the flow detector to turn on a low-voltage relay that in turn turns on the 120V power for the fan - i.e., you want to isolate any non-UL listed device (that flow sensor is a component, not a full device) from 120V power.

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    That isolation is something I'd be comfortable with. And yeah, I have no idea what an inspector would say about this. I also considered the fan speed thing, and Might also put a less conveniently located dimmer in the loop to set the speed down stream of the automatic/manual switch. – aaronP Nov 20 '19 at 18:44

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