AccuServ Heating and Air Conditioning

Advantages of a two stage gas valve

December 21, 2019


Few homeowners know the importance of a furnace’s gas valve. But the gas valve actually has implications on both the comfort of the furnace and energy savings. We advocate a two stage gas valve over a single stage gas valve for a handful of reasons.

The gas valve is responsible for regulating gas flow into the furnace burners. It comes in various designs, including single stage, two stage, and modulating. In this article, we will be focusing on the two most popular designs: single stage and two stage. We’ll be going into detail how each work and why the two-stage gas valve makes a sound investment.

Gas Valves

Gas valves, true to their name, provide the gas to the furnace so that it can properly heat your home. Here an analogy is appropriate: When you use a blow dryer to dry your hair, you are funneling heat via air. A gas valve is much like a blow dryer, funneling gas instead of heat.

Problems with the Single Stage Gas Valve

The single stage valve was the standard design for earlier furnaces. This design allowed two settings: on and off. Regulated by an internal solenoid, the single stage valve allows either all the gas to travel through or none at all. When on, the single stage valve moves as much heat as possible from the furnace to the rooms in your house. That is, the gas valve is blowing heat from your furnace at full blast whenever the furnace is on.

This is problematic for three reasons. First, operating at full blast, the single stage gas valve often uses more energy than is needed. This is especially true on nippy – but not freezing – days, this is often overkill when you only need to heat your home a few degrees.

Second, when a single stage gas valve operates at full blast, it hits the thermostat with all it has, even before the farthest corners of your home are warm. When the thermostat hits a certain temperature, the furnace automatically shuts off. The result is often a furnace that turns off prematurely, leaving you with temperature differences throughout your house – warm central rooms but cold outer rooms, creating cold spots and hot spots.

Imagine blowing a hair dryer on the highest heat setting until your head is burning hot – the heat would become unbearable and you would likely turn the dryer off, even though your head is still wet in most places. However, the rest of your head, such as the back and bangs, might still be wet. A furnace works much like a hair dryer turned to the highest setting: It blows out heat at full blast until the thermostat is hot. But it completely ignores the other – more important – areas that need heat, such as the rest of your house.

Finally, because a furnace with a single stage gas valve turns off prematurely, it will need to turn on once again a short time later. The result is a furnace that is too frequently turning on and off, an action known as short cycling. Short cycling should be differentiated from regular cycling, which is when your furnace turns on and off in regular intervals to keep your house at a comfortable temperature.

To better understand the difference, consider this example: In regular cycling, your furnace might start up running for 10 minutes and then shut off. Three minutes later it starts up again to add more heat to a house that is gradually cooling. This is a normal process of a working furnace.

Short cycling, however, might have a start-up time of 3 minutes. The furnace then shuts off for only one minute before it starts up again. Compared to regular cycling, short cycling has shorter on-off intervals. This is abnormal and can equate to increased component attrition.

Why does short cycling occur? Imagine a chilly (but not freezing cold) Toronto morning. The single-stage gas pump emits a large amount of energy into the furnace, producing heat quickly enough to satisfy the furnace’s thermostat in roughly 3 minutes instead of 10 minutes (which might occur an especially cold winter morning). The thermostat reaches its ideal level and tells the furnace to stop emitting heat.

However, the thermostat’s temperature quickly drops and tells the furnace to restart. This results in a vicious circle. Just as constantly turning on and off any device will stress components, short cycling is not good for a furnace because it wears down components, especially the internal heat exchanger. Hence, a furnace with a single stage gas valve will often need more servicing and parts replacement than furnaces using other types of gas valves.

The Solution: the Two Stage Gas Valve

The two stage gas valve solves the above problems by allowing for two different modes: high fire and low fire. The low fire mode fires at about 65% of the rate of the single stage gas valve; the high fire runs at 100%, like a single-stage gas valve. To return to the hair dryer analogy, a two stage gas valve offers a “low” and “high” setting.

Hence, in comparison to the single stage gas valve, the two stage gas valve is virtually without any tradeoffs. It has the same abilities of a single stage gas valve once it switches from the initial low fire setting.

How It Works

The two stage gas valve is rather intelligent, switching between modes as needed, based on the thermostat. If a two stage gas valve, which starts at the low-fire setting, finds that your house is not heating quickly, it will quickly switch to full capacity to compensate. It will then switch back to low-fire once your house is sufficiently warm.

The applicability of the two-stage gas valve is best explained through its differing uses during different seasons. Because the two stage gas valve always starts up at the more efficient setting (i.e., low fire), it works great in the fall, when you only need a slightly warmer house. But in the winter, the two-stage gas valve will switch to high fire after it finds the thermostat not heating quickly enough with the initial low fire setting. The result is a cost-efficient furnace in the fall and a high-power furnace in the winter.

The slower, more consistent heating of your house typically equates to most homeowners finding that a furnace equipped with a two stage gas valve heats their homes more evenly, effectively reaching the outer rooms before shutting off. In addition, a two stage gas valve works well on chilly days, allowing you to avoid “blow drying your hair on turbo” (i.e., using a full capacity gas valve when it is not needed). The end result is increased comfort for Canadians, who encounter occasional bouts of extreme cold intermixed with moderately cold weather.[1]

Extra Advantages of a Two Stage Gas Valve

But that’s not all. A two stage gas valve reduces short cycling.[2] This means less wear and tear for your furnace.

Moreover, two stage gas valves, being more modern, come with more efficient blower motors. Older blower motors, known as PCM motors, waste electricity. Newer ECM and BPM motors[3] are often equipped in furnaces with two stage gas valves and can help homeowners cut down on electricity costs, saving you over $100 to $200 a year.[4]


Overall, a two stage gas valve can buy you comfort, a reduced need for maintenance, and gas savings. If any of these aspects are important to you, consider switching to a furnace with a two stage gas valve.

Ready to start? Call or click here to today to learn about how much a two stage gas valve can save you!