Types of Harmoniums are varied. Harmoniums are reed instruments played by pumping air through a bellows. The quality of the sound of each instrument is mainly affected by the quality of the wood used, the number of reed banks, and the adeptness of the artist in his or her playing skills.

When selecting a harmonium, it is wise to consider which feature actually is needed and one can make the selection accordingly. Some features sound nice, but in actual use, you might not ever need or use them. Harmoniums are classified by their features. The main features are:

1. Standard harmonium is the basic form of the harmonium which is used by most people in case of artists, performers and for home usage as well.

2. Portable harmonium is a standard harmonium that settles into a cavity and closes to form a suitcase shape.

3. Scale changer is also a simple harmonium with the difference that the keys are not fixed over the reed board. The keys are instead mounted on a movable plate which slides sideways making one key place able on another note.

4. Hand and foot harmoniums have bellows at foot level with the main body at a higher level and connected to the bellows with pipes.

Construction Quality in Harmoniums
The quality of the wood affects the resulting sound. Some of the priciest harmoniums are constructed with hard woods, such as teak or mahogany, which give them a very resonant sound. However, it makes them very heavy to carry around. Harmoniums made from lighter woods, such as pine or fir, are easier to carry, so this should be a consideration while choosing an instrument. If travelling along with the harmonium is the plan, then probably a lighter model can be a good choice.

Standard or Fold-Up in Harmoniums
Standard harmonium models usually have two handles on their sides. They are the classical model and probably most common world-wide.

Some harmoniums fold up, which is a feature that makes the instrument easier to transport. There are two basic types of folding models, one type folds up into itself and the bellows board covers the top. An example is made by the Bina brand. These are a bit tricky to fold and unfold, but once the user gets used to it then travelling along with the same could be a good option.

The other style folds into itself and a separate lid cover the whole instrument. It is called a suitcase model. These are much easier to fold and unfold, and the detachable cover can be used as a stand to raise the instrument to a better playing height. However, they are usually much pricier as they are most often found on harmoniums that are constructed out of heavier wood. And even though they are easier to fold up, they are heavier to carry.

Number and Type of Reed Banks in Harmonium
The sound of the harmonium is affected by the number of reed banks it has. There are harmoniums with 1, 2, 3, or 4 banks of reeds. Usually each bank has a different sounding set of reeds, most commonly called male, female, bass or tenor. Most often, different reeds are placed in each of the reed banks and the mix of sound from them helps create each harmonium`s unique sound.

A greater number of reed banks contribute to the complexity of the overall sound, but more reed banks also means a heavier instrument. More reed banks usually means a wider reach when playing a harmonium. Two or even three-reed bank harmoniums usually have an acceptable reach.

Scale Changer in Harmoniums
Some harmoniums have what is called a key changer, or scale changer. This is a complex mechanism that allows shifting the keyboard to the left or the right. This is a feature that most harmonium players will never use.

Coupler in a Harmonium
Some harmoniums have a coupler, a device that connects one key with its higher or lower corresponding key. When the coupler is engaged, it will play two octaves of the same note at the same time. This has advantages and disadvantages. The advantage is that it can make a harmonium that has a lesser number of reed banks sound like it has more, usually giving a richer sound. The disadvantage is that user will need to pump more air into the instrument to maintain the sound, so one needs to work harder on pumping.

Bellows in Harmoniums
Air is pumped into the harmonium with the bellows. There are actually two sets of bellows, one that can be seen and one that is internal. The external bellows can have 1, 3, 5, or 7 folds.

Bellows can open to the side or the top, and which type the users have depends on the preference. Many, but not all, of the top opening bellows have tighter bellows springs and require a bit more muscle to pump, but ensure that the internal bellows has lots of air. Many side-pumping bellows have a softer pumping action and can also ensure plenty of air for the instrument.

Number of Octaves in Harmonium
Harmoniums are made with differing sized keyboards, which mean that the number of octaves varies from model to model. There can be anywhere form 2.5 - 3.5 (or even more) octaves covered on a model. The models with the shorter keyboards with 2.5 octaves provide plenty of notes for common use. More is not necessarily better because most harmonium players will never use all of the keys on 3.5 octave model. Most models have about 3 - 3.25 octaves.

Stops and Drones in Harmoniums
On the front of the harmonium is usually a series of larger knobs that allow air into the respective air chamber(s). These are called stops. These allow playing one or all of the sets of reeds and controlling the amount of air (volume) to each set of reeds.

Some models have smaller knobs in the front that work the drones. A drone is a fixed note that sounds when you pull the knob to its open position. Most drones are in C#, D#, F#, G#, A#, or a selection of those. It is possible to customize the notes to the preference of the user.