[Chalky (OP)]

Our house isn't that well ventilated, and in the morning, we like to throw the windows open to get rid of the stale air.

If the house gets stuffy through cooking or too many people my lungs don't like it.   So I tend to flush out the warm humid air, by throwing open the front and back doors for a few minutes, before sitting down to dinner.

I heard that cold air warms better or more quickly than humid air, so it's not a bad thing to do.  (Forgive terminology here.)

But it feels counter intuitive as you are throwing out hot air/heat.

Is there any truth in this?

Does fuggy air have different properties?

Heating air from heating systems always seems an odd ill-efficient method of warming yourself, vs direct heating.  Like an electric blanket jump suit!

[alancalverd]

I heard that cold air warms better or more quickly than humid air,

Sort of. Moist air has a higher specific heat capacity than dry air, and fresh cold air will generally be drier than the muggy stuff in a house full of people, so it takes less energy to raise "cold" air by 1 degree than for "muggy" air. But the cold stuff starts off colder, so you have to choose between comfort (dry air) and energy efficiency (stale air).

True greenies use a heat-exchange airconditioner that takes the heat from the outgoing stale air to warm the incoming fresh stuff. Clever system but I think it has to be built into the building design - not sure if it can be easily  added to an existing domestic building as it needs large diameter ducting.

[vhfpmr]

You can buy heat exchanging extractor fans, but it's a bit uneconomical if you're doing more than just one room.
https://www.i-sells.co.uk/kair-heat-recovery-extractor-fan-12vac-selv-humidistat?msclkid=73450987d2651bd0e7895748212c6b73&utm_source=bing&utm_medium=cpc&utm_campaign=EVERYTHING&utm_term=4578778771093910&utm_content=ALL%20PRODUCTS

[Bored chemist]

The heat capacity of water vapour is roughly twice that of air.
But it's unusual for there to be more than 2% or so of water vapour in the air so the overall effect on heat capacity is small.

The biggest difference the water vapour makes is that sweating is less efficient in damp air.
It's probably also noticeable in the way that moisture evaporates from your lungs, nose + throat.

[vhfpmr]

Is it  water vapour that makes air feel stale, or carbon dioxide?

[Bored chemist]

Is it  water vapour that makes air feel stale, or carbon dioxide?

Could be both

[WilliamLeblanc]

GET RID OF STALE AIR!
There are a number of steps that you can take to prevent stale air in your home, school or office without causing a considerable increase in your monthly energy bill. The main thing that you should think about is increasing the ventilation in the affected rooms. Your HVAC system, when working properly, should filter out stale air and replace it with fresh air. This will help dilute any humidity or MVOCs causing your room to feel stuffy. You can also increase a room’s ventilation by:

    Installing a window fan in the room. Some window fans have settings to pull stale air outdoors. Make sure to follow the manufacturer’s instructions to ensure efficient ventilation.
    Using exhaust fans in your kitchen, bathrooms and laundry room. Exhaust fans help get rid of stale, humid air. This is especially important in any enclosed rooms in which moisture tends to build up.
    Changing your HVAC filter regularly. A dirty or clogged HVAC filter will decrease the efficiency and effectiveness of your ventilation system. Additionally, if mold or bacteria has started growing on your filter, your heating and air system could be blowing these pollutants back into your home. If you have not already, consider switching to a HEPA filter to further reduce the levels of airborne pollutants in your indoor air.
    Opening your windows. If the outside weather allows (and the pollen and mold spore counts are low) opening your windows can be a great way to introduce fresh air into your home.
    Using an air purifier. An air purifier can help provide fresh, clean air to your home. Many traditional air filters can only capture particles, which would not be helpful with unpleasant smells.