That stuffy feeling has a number attached

A group sits down to eat, the windows are shut, the air conditioning is on, the conversation is good — and then somebody yawns. Most people put it down to a full stomach. Half of it is the air.

Breathing produces carbon dioxide. One person in a closed room measurably raises the level within an hour; six people do it six times faster. By the time it feels "a bit stuffy in here", the concentration is usually already high enough to affect how clearly you think.

What makes this awkward is that CO₂ has no colour and no smell. You just feel tired, slightly headachy, less talkative — with no idea why. Put a sensor in and a vague feeling turns into a number you can see.

Numbers worth remembering

What happened over those two hours

1. 18:00

   Before anyone arrives

   Empty room, CO₂ at 480, much the same as outdoors. The system is just watching.

2. 18:10

   Six people sit down

   The line starts climbing, faster than you would expect. Nobody feels anything is wrong yet.

3. 18:40

   Past 1000

   A message arrives: the dining room air is getting stuffy, open a window. Your body has already noticed by now — you have just attributed it to the meal.

4. 19:10

   Past 1400, message ignored

   Everyone is deep in conversation and nobody got up. The system stops asking and turns on the circulation fan or fresh-air unit itself.

5. 19:30

   The line turns

   Ventilation takes effect and the level falls back under 1000. Someone might say "was it a bit close in here earlier?" — but it has already passed.

6. 20:00

   Table cleared

   People disperse, the level settles back into the 700s on its own, and the system switches ventilation off. Nobody had to deal with any of it.

Four things it takes care of

Different homes, different thresholds

What you need to have

Home Assistant calls every device an "entity". The brand and model do not matter — what matters is the category it falls into.

How the whole thing works

Use the ready-made blueprints

The hub ships with 22 tested automation blueprints. Think of a blueprint as a fill-in-the-blanks form: the structure is done, you supply the content. This scenario uses two — entity_state_trigger_notify for the alert and greenhouse for the ventilation.

Just say the word

The WOOWTECH hub ships with HA-MCP, which lets AI connect straight into your system, build the rules, and then check for itself that they really fire. All you have to do is describe the outcome you want.

Prompts you can copy straight across

Every block below can be copied whole with the button on the right. Pick the one closest to what you want — you do not need all five.

Check whether there is a CO2 sensor in my dining room. If there is,
build one rule: when the reading goes above 1000, push me a
notification telling me to open a window, and put the current
reading in the message. Just that one rule for now.

Build me two separate dining room air quality rules — keep them
apart rather than rolling them into one. The first is the nudge:
CO2 above 1000 pushes a notification to my phone with the current
reading in it, only between 7am and 11pm so it never wakes me.
The second acts on its own: above 1400 it starts the circulation
fan or fresh-air unit and keeps it running until the level falls
back to 800, active all day and with no notification at all.
If there is a powered or vent window, open that too and let real
fresh air in first. Use the ready-made blueprints on the hub
rather than writing your own from scratch. When it is built, test
it yourself, confirm it really fires, and tell me which devices
you used.

Our dining table doubles as a desk — the kids do homework there and
I work there during the day, so we need to stay sharp. Tighten the
thresholds: nudge me above 800, start ventilating above 1100, and
still stand down once it falls under 800. Make the alert window
7am to 10pm and leave everything else as it is.

The alerts come too often. Move the nudge threshold from 1000 to
1200, and only notify me once per episode instead of every few
minutes. Do not touch the ventilation rule at all. Tell me what
all three numbers are once you have changed them.

I picked these thresholds off the top of my head and I want to know
whether they actually suit this house. Line up the past seven days
of dining room CO2 and compare them: what time of day the air
usually starts going stale, how high it peaks, how long it stays up
there. If the real pattern does not line up with 1000 / 1400 / 800,
propose a set that fits our routine instead, and say which days led
you there. Hold off on changing anything until I say go.

Common questions