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Community and Q&A

Make up air and multi zone sensor

D.Kits | Posted in Mechanicals on

I do instal 600cfm rangehood in my kitchen. Vented outside of course. I have also motorized damper supplied by the manufacturer and it will be installed on the dedicated make up air duct being controlled by the switch on the hood. This part is clear. What is less understood is the question of preheating this make up air supply. The climate is cold up here and air, if not preheated, will mess up the whole system. Of course, company like Fantech offers elegant solution but… what if… Ecobee makes a thermostat with multi zoning temperature control sensors. So what if one of the sensors will be installed onto the furnace duct above from where my rangehood dedicated make up air gets in. Then cold air from outside will trigger the sensor, which then, through the main thermostat will trigger the furnace. Will that become a possible budget solution?

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  1. GBA Editor
    Martin Holladay | | #1

    D. Kits,
    It sounds like your makeup air is being introduced into a furnace duct. I'm not sure exactly which furnace duct you have chosen or where the duct is located, but presumably the temperature of the makeup air will be tempered with air from your furnace -- heated in winter -- and your wall-mounted thermostat will keep the furnace operating until the thermostat setpoint is reached. I can't see how introducing an additional control sensor in your ductwork will help.

  2. Jon_R | | #2

    Not clear how it would "mess up the whole system", but I expect your plan would lead to overheating of the interior and rapid cycling of the furnace.

  3. D.Kits | | #3

    I understand the second response. I guess I was not clear enough. So, in theory, if I will get my fresh air intake connected to the central air return it will start introducing the cold air into the building to compensate for the amount which range hood takes out. Understood. It will take too long for the thermostat installed in the living room to get furnace back to work and start heating again. The temperature fluctuations and cycling and other consequences are imminent. But, what if my temperature sensor is installed early enough to sense that the cold air is coming and will kick in the furnace? Then the second sensor in the room will say that temperature achieved the required level and will make furnace stop? Isn't it how multizone sensors are communicating with thermostat. Here is the answer I have received from the Ecobee support today: "Yes, in this case, you can use the wireless remote sensor for monitoring and averaging the temperature as long as it is within 40 feet range of main thermostat and surface is not too hot to make the plastic on sensor melt." In reality instead of placing 2 sensors in the different rooms (call it a zone or whatever it is) I will put one in the room and one on the supply plenum early enough in the path. Would it become a solution for preheating the cold return air? Thank you very much for your help!!!

  4. GBA Editor
    Martin Holladay | | #4

    A thermostat sensor in the supply plenum will read temperatures ranging from 68 degrees F to about 140 degrees F or 150 degrees F. These are not the normal range for a thermostat.

    One possible problem: If your supply plenum is located in a cool location -- for example, your basement -- a thermostat in your supply plenum might initiate a call for heat when your supply plenum is at 68 degrees F. But just because your supply plenum is cool, doesn't mean that your living room and kitchen are cool. They may be warm and toasty.

    There is probably a way you can set the thermostat to address these issues, but I imagine it would take a lot of trial and error (even if the sensor doesn't melt).

  5. SwitchgrassFarmer | | #5

    D.Kits, perhaps what you want is more "relay" than "thermostat".

    When your outside air make up damper is controlled open, a relay could also engage the blower motor (only) on your furnace. The return air flow into your furnace would temper the cold make up air. Eventually the overall air temperature in your home would drop, and your thermostat elsewhere would call for heat, thus maintaining a constant temperature.

  6. user-1085194 | | #6

    Why not install the make up air supply in the kitchen close to the exhaust hood where it is needed? This eliminates the issue of cold or hot humid air being injected into the main return and how to deal with it. The make up air being directed at the source of the heat and odors limits its effect on the rest of the home.

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