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Ensuring that kitchen extract is running before lighting stove top

mark_gil | Posted in General Questions on

We’re building a ‘pretty tight’ house, but will be installing (not ideal, but a choice) a large gas burning range top into the house.  In order to manage the indoor air quality, we’ll be adding a high-capacity range hood (c1000 cfm), and matching make-up air (likely Fantech MUA) with the make-up air delivered to the immediate vicinity of the stove top (luckily we’re in CA in climate zone 3 and have a relatively benign exterior temperature range to deal with for the inflowing air). 

All that said, we want to make sure that it’s not possible to start the range (either gas flowing, or ignited) without the extract running.   Has anyone found a good solution to achieving something like that?

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  1. Expert Member
    Akos | | #1

    Awfull lot of complication to get a stove that doesn't work as well as a professional induction range.

    I have both gas and induction at home and the gas only ever gets used for overflow when all induction elements are in use. The induction is hotter, faster, better heat control. Plus I never burn my hand on handles like over the gas burner. The only thing to make sure is to get a stove with knobs, touch controls are great for a clean decorative kitchen but the worst interface if you actually cook.

    If you must have gas and you want to lock it out, you can look at a gas shutoff device used for residential fire suppression system such as this:

    I've installed their electric range shutoff unit before with their suppression system and works quite well.

    You would wire a current sensing relay onto the power supply of your vent hood and have it connected to the gas shutoff device.

  2. DennisWood | | #2

    I'd second induction over gas 100% if you have choice. Faster, better control and no need for a massive exhaust fan either.

    I've automated our exhaust fan to induction, by using a zWave 240 volt (Aeotec) switch which is connected to the induction cook top 220 V power. An Aeotec micro relay (also zWave) turns the fan on and off based on power to the cook top, although you can still control via the manual fan switch. It works great and ensures the fan is on when cooking, and off when not.

  3. walta100 | | #3

    It seems GE offers a “Chef Connect” feature that can be set to start the fan when a burner is turned on if you buy both a GE range and hood.

    I see some of the Samsung hood also have automatic features.

    Try googling “Heat sensing range hood”

    I like my induction cook top.

    Try convincing the cook to opening their mind to the possibility that technology may have improved in the last 50 years and to at least test drive an induction top at a kitchen showroom


    1. Expert Member
      DCcontrarian | | #4

      Intuitively it seems that you're better off trying to have the fan come on automatically rather than keeping the stove from operating.

  4. Expert Member
    BILL WICHERS | | #5

    If you are using an induction cooktop (which has a lot of advantages in a tight home), then an interlock like this is pretty easy to do. Get a big contactor (a contactor is basically just a beefy relay) that is rated to carry the full load of the cooktop, which is usually 40A or 50A. Contactors like this are commonly using for blowers and other parts of HVAC systems, and will be available from mechanical supply houses, but you can also get them from Grainger. You'll need an electrical box to house the contactor too, I would use a suitably sized metal box, which will probably mean a trip to an electrical supply house. A common size that would likely work would be 8x8x6" deep. Use the contacts on the contactor to supply power to the cooktop, so the power for the cooktop would go to the contactor first, then to the cooktop. The easy way to do this would be to use the box you put the contactor in as the junction box between the cable bringing power into the kitchen and the whip on the cooktop.

    If you get a contactor with a 120v coil, you can wire it into the range hood so that the fan that turns on the exhaust fan also energizes the contactor. In this way, the contactor will only allow power to flow to the cooktop when the exhaust hood fan is on. You would have to turn on the fan first before the cooktop would be energized. Note that if you turn off the exhaust fan, you would also shutoff the cooktop, and that might defeat any features of the cooktop such as running an internal cooling fan for a while to cool things down after use. Ideally you'd want to check with the manufacturer first to make sure there is no problem doing this, but it should work.

    With gas, you would need an electrically operated gas valve (which are also available from mechanical supply houses), and things would work similarly but with the gas valve interrupting the flow of gas instead of the contactor interrupting the flow of electricity.

    If you want to make sure there is actual airflow and not just that the fan is on, then you need a device known as a "proving switch", which is a sort of differential pressure sensing switch. These are commonly used in combustion appliances to make sure there is ariflow from a combustion blower prior to lighting the flame, and they are available from mechanicaly supply houses too. To use one of these, you need to set it up with the sensing tubes so that it watches the pressure on both sides of the exhaust fan. These switches usually are rated for 24 volts, not 120 volts, so you would need to use a contactor (or gas valve) with a 24v coil, and you'd need a 24v "control transformer" (back to the mechanical supply house again) to get the 24v power to run the system. With the proving switch, you can keep the transformer powered all the time, so no electrical modifications to the hood, and let the proving switch alone control the system.

    Note that if you have an induction cooktop, there is another way to do this that might be more user friendly. Get a device (mechanical supply house again, but electrical supply houses have them too) known as a "current sensing relay". These are "relays" (usually a little fancier than that) that can sense when current is flowing in a wire. These are commonly used to detect when motors are running, but can work in all kinds of applications. Set the current sensing relay up to monitor the power supply to the induction cooktop, and use it to control the exhaust fan. With this system, the cooktop will operate normally all the time, but when you turn it on and it starts drawing power, the current sensing relay will also turn on the exhaust fan automatically. I'd prefer this setup over the interlock that requires the fan to be on before the cooktop would work. You can set this up with gas too, but you'd need a gas flow switch and those are much less common devices.


    1. mark_gil | | #6

      Thank-you! Some great ideas here.

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