> Genuine, this-never-occurred-to-me question: are there lots of people out there with boilers that DON'T do this, or areas where it is not normal?
I understand that american indoors heating is mostly done through HVAC. Since in that case the heater would be heating the air directly, you'd need a separate boiler. Heating water to heat the air makes sense when water is your transfer medium (e.g. hot water radiators), less so when the air is.
So I expect US homes usually have separate air furnace and boiler, whereas in e.g. europe where water central heating is common you'd usually have a combined furnace/boiler.
I understand that american indoors heating is mostly done through HVAC. Since in that case the heater would be heating the air directly, you'd need a separate boiler. Heating water to heat the air makes sense when water is your transfer medium (e.g. hot water radiators), less so when the air is.
So I expect US homes usually have separate air furnace and boiler, whereas in e.g. europe where water central heating is common you'd usually have a combined furnace/boiler.