Say you pack the average house absolutely full of 100% carbon dioxide gas (or any heavy gas), but the doors and windows are typical American homes. How long does it take for, say, half of the nitrogen to seep out the tiny cracks and vents and fireplace chimney?
If the house is 100% packed with CO2, no nitrogen is there. If you’re waiting for half the CO2 to leak out, that time depends on the building construction. In our old desert adobe with gaps in the floorboards, I’d expect CO2 seeps to kill all the subfloor scorpions rather fast. Our current house is a sealed-tight modular so CO2 loss will take a long time.
Yeah, “average” and “typical” are gonna be difficult. A leaky old house built in the 20s vs a McMansion built in the 90s will deliver very different results.
Newer construction homes are sometimes so airtight they can cause indoor air quality problems for the occupants.
It’s going to entirely depend on the house. My house, for example, while mostly ‘modern’, has garbage, contractor grade windows that I’ll bet didn’t cost more than a hundred bucks a pop. They leak like a sieve. They look like modern vinyl double pane windows, but air pours in between the sashes. Enough that on a windy day the vertical blinds actually move around. There’s a constant cold draft all winter long.
A house built with similar construction, but better windows and doors would take much longer to turn over all the air than mine.
If you used spray foam insulation, you’d probably start to approach almost no unintentional air cycling between the conditioned and unconditioned/outside air.
You mentioned tiny cracks and the chimney, but with some added cost, both of those can be closed up pretty easily.
To get a real idea of how much your house leaks, you’d have to get it tested. I have no idea how expensive it is, but IIRC, all they do is put a fan in the door or window blowing outward and measure how much vacuum it creates inside the house. Similarly, I believe they can have the fan blowing in and use a fog machine to find the leaks.
My house was built in 97. There’s a tube going from an HVAC duct to the outside of the house. After some research, I found that it’s required on modern houses to bring in fresh air when the stove or bathroom vent are turned on. Either (or both) because the houses are so sealed up the exhaust fans can’t actually exhaust anything or they’re sealed up well enough that the end up drawing air in through the ‘wrong’ places, like the soffits (which brings in dust/mold/humidity) or cracks in the foundation (which can bring in radon).
This vent gives the air an easy way to not only enter the house, but then get drawn through the furnace filter and, if the furnace/AC is running, the fresh air will get heated/cooled first.
I spent 5 years as a HVAC installer once upon a time and that is the purpose of the fresh air duct but they are typically set on a timer rather than being linked to exhaust fans.
They are required by law to be installed but my boss considered them useless and an energy waste (bringing in cold air in the winter & hot air in the summer) for everyone except shut-ins. He would frequently show homeowners how to deactivate the vents themselves if they wished to do so.
There’s no inline fan on mine. It’s literally just a piece of (insulated?) flex pipe that goes from the side of the house to a return duct.
In this case, it’s totally passive. It’s not meant to bring fresh air into the house for the sake of bringing fresh air into the house. It’s just giving the makeup air a convenient way to get into the house when an exhaust fan is running. For air to leave the house it has to come in from somewhere, better here than though the foundation or attic.