Home Assistant

At a glance

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

• Plain fact: Switches on your monitor’s reading
• In its favour: Reads Aranet4, SwitchBot, Qingping and AirGradient monitors locallyOver Bluetooth or your own network, with no cloud. INKBIRD has an integration too; CO₂ was confirmed for the IAM-T1, not the IAM-T2.
• In its favour: Its Threshold helper switches on and off with a gapSo it can turn a relay on above 750 and off below 650.
• Worth knowing: Needs an always-on computer and a dry-contact relayPlus a check of what happens if the computer stops with the relay closed: it can stay on high.
• Worth knowing: No ventilator maker documents itZehnder’s ComfoConnect integration is unofficial and marked legacy.

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. Make an automation: relay on above 750 ppm, stays on at least 15 minutes, off below 650.
2. Set the relay to stay off after a power cut, or to switch itself off after a while.
3. Unplug the hub once with the relay on, and check the unit goes back to its normal speed.

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: Units with a low-voltage input that holds high speed while closed, through a dry-contact relay. No ventilator maker documents it.

• 

  Zehnder ComfoAir Q350 ERV

  DIY smart-home option

  201 cfm at 0.5 in.

• 

  Zehnder ComfoAir Q350 HRV

  DIY smart-home option

  195 cfm at 0.5 in.

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

Specs

Runs on

A small always-on computer at home

Monitors it reads

Aranet4 (firmware 1.2.0+), SwitchBot Meter Pro CO₂, Qingping CGP22C and CGDN1, AirGradient ONE; INKBIRD (CO₂ confirmed for the IAM-T1)

Relays

Shelly, Z-Wave (Zooz), and others

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

Smart-home pieces

Use a monitor you already own to switch high speed. Not documented by any ventilator maker: low-voltage inputs only, and check your manual first.

• Shelly 1 Gen3

  Switches on your monitor’s reading

  Wi-Fi relay with a dry contact

• SwitchBot Bot, triggered by the Meter Pro CO₂

  Switches on your monitor’s reading

  A button pusher, no wiring

• Zooz ZEN17 universal relay

  Switches on your monitor’s reading

  Z-Wave relay with dry contacts