> forced air

It has as a fan and blows heat.

If you have a fireplace or radiator, it just gets hot and doesn't actually blow it.

> a furnace

Burns something for heat. This can be natural gas which is piped to the the house, or:

> liquid propane vs heating oil

Propane is an explosive gas. It burns up in a couple seconds.

Oil is not explosive, it burns very slowly and releases more heat, but often produces more smoke.

Oil is safer and easier to haul. Theoretically it might freeze and become buttery in very cold conditions.

> "central"

One unit for multiple rooms. You have ducts (big pipes) that can blow hot air through multiple rooms.

> geothermal

If you place a big container of water in the freezer, it might take days to freeze. The outside can freeze while the inside is warm.

If you have a big mountain, it heats up slightly in the day, and cools down slowly at night. But because it's so different the temperature stays pretty constant. Sometimes it's even constant throughout the year.

If you did a hole that's deep enough, it just keeps getting warmer underground. There's so much dirt that it weighs a lot and won't freeze easily. Eventually if you go super deep your get hot lava.

With geothermal you dig a hole or trench that's deep and run a water pipe through it. When you put cold water in the pipe, the heat deep in the ground will heat it up so you get warm/hot water on the other end.

> boilers

A fire or electric heat that boils water. These are used for big buildings.

Instead of running ducts with hot air.

They run pipes with steam or boiling water.

> Radiator

The hot water from a boiler flows through it and makes it hot. There's no fan, and sometimes they don't even use electricity.

https://upload.wikimedia.org/wikipedia/commons/0/02/Household_radiator.jpg

It just gets hot, and as a result sometimes one side of the room is hot and the other is cold.

If a fan is added it can be a hydronic system and it evens out the temperature better. With a hydronic system, you can also pump cold water and use it as an A/C.

> heat pump

An air conditioner has two ends. One blows hot air, one blows cold air.

Normally you want the cold air to blow inside, and the hot air to blow outside.

It turns out if you run an air conditioner backwards, it will blow cold air outside, and hot air inside. This makes it surprisingly effective as a heater.

An A/C actually produces more heat than cold.

Let's say it's 10 degrees outside. If you cool the outside part of the A/C to zero degrees.

The 10 degrees air actually warms it up from zero to ten degrees.

Because of this, a heat pump can actually grab little bits of heat from outside and it's one of the most energy efficient ways to heat a house.

> mini splits

An A/C has a hot side, and a cold side.

With a mini split you leave the hot side outside, and the cold side inside.

These are connected with pipes instead of ducts.

Pipes end up being more efficient than ducts.

With a central system you have one system for the whole house, or 2-3 zones in a house.

With a mini-split you can have one system for each room.

These systems can each have their own outdoor box, or they can share a big outdoor box.

Mini-splits are especially easy to run backwards and use as a heat pump.

By heating/cooling just the rooms you need you can save a lot of power vs heating/cooling your whole house.

> baseboard

A heater on the bottom of a wall: https://images.thdstatic.com/productImages/a8027bb7-12b0-4200-93c8-260d3ff7c00f/svn/whites-cadet-baseboard-heaters-ebhn1500w-4f_600.jpg

> window units

Mounted in a window. Typically these are air conditioners, but some can do heat as well.

Since they're in a window they can blow the hot air outside the window, and the cold air inside.

They don't need any ducts, pipes, etc.