Single Stage vs. Two Stage Condenser

Single-Stage, Two-Stage? What does it mean when someone uses these terms? Well there are two things they could be talking about. One is a furnace with different stages, and the other is a compressor in an air conditioner (or heat pump). A single stage unit will have 2 settings, on… and off. This means it will run at 100% capacity when turned on until it raises or lowers the temperature to the desired amount and then shuts off. A two-stage unit will have two on settings as well as off. This means it will turn on to less than full capacity for the first stage: If this does not get it to the desired temperature it will turn on to the second stage at 100% otherwise it will turn off. Stages in Compressors Motors A two-stage compressor runs at 40% in the first stage and 100% in the second stage. This allows you to have more control over the temperature in your home which would make it more comfortable. It will also help in the cost savings department. For example, if you have a 4-ton two stage air conditioner and the first stage (40%) can handle the temperature then you are only using the electric of a 2 ton. Here are a few graphs demonstrating the benefit of multiple stages On high end models you may see the term Variable Speed. They use this term in reference to motors, which is why you see it for both compressor motors and blower motors. Another meaning would be multi stage, for example on the Air Quest model HVA936GKA here is the breakdown

Stage	Capacity	dBA
1	25%	56
2	50%	60
3	69%	65
4	88%	66
5	100%	67

Variable speed also means that it can run at a quieter noise level. Unfortunately, the variable speed option can only be controlled by expensive thermostats. You can use a 2 stage cooling thermostat with these variable speed condensers but you will not get the full benefits of the 5 stages they are capable of. For a variable speed blower motor, it functions like a Rheostat for example in model AVPTC25B14AB It has a CFM range of 395 to 1105 Stages in Furnaces A single stage and two stage furnaces will operate in a way that is like the single and two stage compressors. Two stage furnaces will operate at 70% capacity and then 100% capacity if the first stage does not bring up the temperature enough. This capability allows the furnace to keep the temperature closer to the desired amount. Gas furnaces also have a modulating option which is like variable speed but even better. It would be comparable to the gas pedal in the car, push a small amount and very little gas is used, press all the way down for full capacity, or press anywhere in between for desired amount. With the ability to keep and hold the temperature closer to the targeted amount and the furnace can save quite a bit of energy by only using the amount of gas it needs. This means lower energy bills!! Here is an example of modulating furnace temperatures Two stage and single stage look very similar to the two stage and single stage compressor. Multi stage furnaces also have the benefit of lower noise levels. With a modulating furnace you would not even hear it most of the time. Some of the modulating furnace models need a special thermostat to work. As technology progresses furnaces and compressors will be increasingly pre-programmed for modulating or variable speed so you can use a normal thermostat. Costs The most efficient models are the variable speed and modulating. They come with the drawback of a high upfront cost, up to $1000 more than a regular single stage furnace. This can be a large pill to swallow but it is a long-term investment. If you plan on staying where you’re are for a long time, then a multi stage system may be right for you. Your wallet will thank you later, and so will your spouse. If you have any questions contact us here at HVACDirect.com and we will help you pick the system that is right for you and at a great price.