I don't understand how central heater heats up a whole house

I grew up in a small farm house with no AC.

In fact I never knew much about it until I visited an aunt in the city and I heard her complaining about the poor climate control in her living area.

She lived in a bungalow with 4 bedrooms and a stretched out garage where she kept most of her old household appliances. She’s a hoarder, and among her things in the garage are a traditional cooking stove, cooking table top, a 2-face commercial air conditioning unit and a low powered heater. These were from her business that closed down a few ago after she couldn’t meet the local health regulations in her eatery. A local service provider who mostly deals with commercial HVAC for sale had bought most of her business equipment. So back to her house that had several units of independent ductless mini split spread across most rooms. I couldn’t believe she used to rely on a central AC system to warm or heat the whole house. I understand it was a lot of ductwork all around the house and as the house she built 30 years old aged, a/c service was becoming costly. So she consulted a local a/c representative that recommended a more modern and efficient furnace/heater installation. These new units demand infrequent a/c repair and heat pump service. I liked that technicians often offer useful energy saving tips but the ultimate advice was to google more about air conditioning. It was good to learn how attics vents play a pivotal role in heating and cooling bungalows by relying on the help of a dehumidifier, something that you can achieve by buying a heater for sale.
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