Zehnder CO₂ sensor (0–10 V) with the Option Box

At a glance

• In its favour
• Plain fact
• Worth knowing
• Not stated by the maker

• In its favour: Can be set under 800
• In its favour: Made for the ComfoAir Q350, Q450 and Q600Wired to the Option Box, which has four 0–10 V inputs. The Q unit has no boost or 0–10 V terminals of its own.
• In its favour: Ramps up gradually, toward a settingThe Q unit works to hold the room at the setting. With several sensors, the highest reading decides.
• Worth knowing: Use sensor mode, set to 700 ppm (3.5 V)In its own controller mode it holds a fixed 1,050 ppm, and Zehnder’s suggested setting is 1,000. Both are above the 800 goal.
• Worth knowing: Its light stays green up to 1,200 ppmGo by your monitor’s number, not the light.
• Not stated by the maker: The lowest setting it allows isn’t statedZehnder’s mapping makes 3.5 V 700 ppm; its manuals don’t give a floor.
• Plain fact: A manual override goes back to automatic within 12 hours

Setting it for a bedroom

HouseExhale’s setting: switch up at 750 ppm and back at 650, or ramp from 600 to full by 750. Never above 800.

1. Put the sensor in sensor mode.
2. On the Option Box input: input at 0% = 10.0 V, input at 100% = 2.0 V, method CONTROL, setpoint 3.5 V (700 ppm), proportional band 50%, integral time 300 s.
3. Check with your own monitor over a few nights that the bedroom averages 800 or less.

A Danish study ran a bedroom fan from about 900 ppm and the nights still averaged 835, so a control has to start below the goal. Good home CO₂ sensors are rated within about 55 to 90 ppm at 800, and the night average includes the climb after bedtime, so 750 on and 650 off leaves room for both. A control in the return duct mixes the bedroom with empty rooms, so it needs lower settings still (about 650 on, 550 off), and your monitor in the bedroom has the final word. These are HouseExhale’s numbers: no study has tested a control against an 800 night average yet.

What it works with

Documented for: Zehnder ComfoAir Q350, Q450 and Q600 (with the Option Box).

• 

  Zehnder ComfoAir Q350 ERV

  Documented by Zehnder

  201 cfm at 0.5 in.

• 

  Zehnder ComfoAir Q350 HRV

  Documented by Zehnder

  195 cfm at 0.5 in.

How to add CO₂ control to an HRV or ERV · HRV and ERV units

Specs

Output

0–10 V: 2 V is 400 ppm, 10 V is 2,000 ppm

Power

12 V DC from the Option Box

Modes

Sensor (sends the reading) or controller (holds a fixed 1,050 ppm)

Option Box

Four 0–10 V inputs, each set separately

Also works with

ComfoAir 200, SL, 330, 350 and 550 (Zehnder Switzerland)

Part numbers

Sensor-CO2-Wall Mount, SKU 9767-00 at Zehnder America’s store; the ComfoAir Q350 spec sheet lists 9260-01. Option Box 9620-00 on the same sheet.

From the maker’s documents, read October 17, 2026. Prices are before tax and shipping and change often.

Made by the ventilator’s maker

Sold for a maker’s own units, with the wiring in its manuals. An installer fits them.

• 

  Fantech CO2RT-R (item 99315)

  Setting range not published

  Wall CO₂ controller with a relay

• 

  RenewAire CO2-W (wall) and CO2-D (duct)

  Can be set under 800

  CO₂ controller with a relay, for RenewAire ERVs

• S&P SCO2-W

  Can be set under 800

  Wall CO₂ control for S&P ventilators