New Furnace Technology: What is it and What Does it Do for Your Home?
November 6, 2017
Like any other industry, the home heating industry continues to innovate with new heating technology for not only furnaces but heating systems that use renewable fuels as well. If you’re like most people, your first reaction is what could really be that different? You burn fuel to make heat then get a big blower to move it around your duct system. From that standpoint, you’re right; there’s a ‘plant’ that creates heat and then a blower moves it around. The differences are all in what kind of energy is used to create the heat, how much heat is produced, and how aggressively is it distributed throughout the house.
In the beginning, there were ‘single stage’ furnaces. The furnace itself was either on or off, and if it was on, it produced its maximum heat and distributed it at maximum speed. In fact, only recently (because of legislated code changes) have new homes contained anything other than these single stage units. What’s wrong with these units? Before we go into that it might be useful to take a step back and remember how forced air heating systems work.
The ‘brain’ of the forced air system is the thermostat on the wall. It senses the temperature in the house (at the location of the thermostat) and compares it to the setpoint. If it senses a temperature lower than the set point it sends a signal to the furnace to fire up (a call for heat). A single stage furnace will continue to produce the maximum amount of heat it can until the thermostat gets satisfied (the temperature at the ‘stat is equal to the setpoint). We all know how much the weather can vary in Southern Ontario – so that the amount of heat we need varies as well. Think about it – do we need as much clothing when we go outside in November or April compared to how much we need on a February night? Of course not. So what happens with a single stage furnace since it produces the same amount regardless of conditions? It just runs longer to satisfy the ‘stat. Think about what’s happening. When the heating load is high (very cold outside), the furnace runs a longer time to satisfy the stat. If the duct system is designed well and the vents are dampered properly, the air will get to the furthest corners of the house (far away from the ‘stat). On the other hand, when it is milder it doesn’t run for nearly as long. Again if the duct system is perfect, an equal amount will get distributed all over the house. In our experience, not only are systems not installed properly, they are vented even worse. Because air travels the path of least resistance, the new, warm air will want to escape the duct system as quickly as possible. This means most of the air will be exhausted out the vents closest to the furnace – which coincidentally is most likely where the ‘stat is. So what happens? The furnace runs for very short periods of time, the ‘stat gets satisfied, and the furnace shuts down – all with minimal warm air getting to the second floor or areas further away. People close to the ‘stat are comfortable, and those far away are no warmer at all!
So what changes to furnace technology have they made? When we look at fuel based furnaces (propane, oil, gas), 95+% of the innovation is focused on how to improve the comfort level all over the house when the heating load is less than maximum. What have they done? They’ve developed technology that not only fires the furnace at fractional rates but also matches the fire rate with the fan speed. This way not only is fuel saved (lower burning rates) but less electricity is used (slower fan speeds).
The first innovation on this front was the ‘2 stage variable speed’ furnace. As its name suggests, the furnace can fire at a low and a high speed, and the fan speed is completely variable. When the ‘stat calls for heat, the furnace fires initially at low speed with an appropriate fan speed. If the ‘stat is not satisfied within a set period of time (< 2 min), the furnace will automatically fire up to full speed on both the heat and blower settings. This technology really shines in the shoulder seasons. After we switch to heating season (the furnace plays a little catch up), we will go almost a month and a half before we ever hear the furnace click into high speed.
Once the engineers got onto this variable firing and blower speed train, they got really creative. The next generation morphed into infinitely variable firing and blower speeds. Instead of waiting for the ‘stat to call for heat, it measures outdoor temperature and the artificial intelligence of the furnace (communicating with the ‘stat) tells the furnace how hard to fire. Ideally, the furnace never shuts down and it produces just the right amount of heat to keep it at the set temperature. This really improves the efficiency of the unit so the customer ends up paying much lower gas bills.
So basically what all of the furnace manufacturers have developed is ways to make you equally comfortable no matter what conditions are outside. This new furnace technology has made it possible to have just the right amount of heat being produced and distributed in the home.
Posted in: Heating