Why is my 2 Stage Furnace Always Running?

After our talk on short cycling, we came across people with the opposite complaint: their furnaces were running constantly. As opposed to constant short cycling, these people were experiencing some form of long cycle. Their furnace would fire up, warm the office, and then keep running. There would be constant, mechanical sound from the machine. This is exactly what it’s supposed to do.   Wasted Heat In a single stage furnace, the thermostat calls for heat, the furnace runs, and once the target temperature is reached, it all shuts down. This is horrendously wasteful. Your furnace has just  burned fuel or used electricity to get a heat exchanger red hot. When the furnace shuts down, that heat exchanger is still roasting, glowing red, but its not using that heat. The heat exchanger will just sit there, cool down, and an extra ten, twenty, or even thirty minutes of warmth has just been completely wasted. The excess heat in the exchanger will go into the ambient air in the furnace. It might heat some of the basement or perhaps the furnace will have a tiny bit less work to do next time. In any event, it’s resources spent that aren’t making you more comfortable. This situation is analogous to approaching a red light, flooring the car, and then slamming on your brakes. All that gas to speed up is probably being burned for nothing.   Using Idle Heat There’s not really much […]

Read More →

What is Short Cycling?

Everything around you is designed with a specific set of uses. Consumer lighting is generally designed to be in a warmer environment, be turned on for a few hours, then be shut off for a few hours. Your car is designed to start up, run for at most a few hours, reach a few thousand rpm, carry a given load, and then shutdown for a while. Everything is designed with these use constraints, that they’ll be on for a given time, achieve a given performance, and then shut down. We call this off, on, off pattern a Duty Cycle.   Getting Out of Cycle Your car works wonderfully when you use it as its designed, doesn’t it? Short trips to the store, the commute to work, and the occasional long haul trip all work out just fine. What would happen if you didn’t use it as intended? Imagine if you ran it for short periods. Start up, drive to the stop sign, shut off. Start up, drive 5 minutes, shut off. Start up, drive around the corner, shut off. Something is going to break eventually. Either the starter will have overheated or the battery will die, but it’s going to work a lot shorter than desired because it’s designed Duty Cycle is being interrupted. This disruption, a constant start-stop is short cycling. The system keeps going through cycles, but they’re shorter than they should be. Just as with the car, […]

Read More →

Unfreezing a Freezer

How do you run your refrigeration hardware through the winter? How far does our industry go to keep a fridge running in the winter or a hospital chilled in a blizzard? There are a number of technologies at play, all working to manipulate the hardware to do their bidding. These are collectively called Defrost Controls.   Let Nature Take Its Course The simplest defrost system is little more than a few switches and a timer. In many systems, the greatest concern is that the evaporator coil may freeze over. This is especially common with industrial freezers. This is a year-round problem and it can be caused by staff frequently entering and leaving a freezer. The freezer temperature increases and many refrigeration systems end up running for entirely too long. The evaporator coil builds up ice from being chilled too much. In configurations like this, the simple solution is a time delay. The compressor shuts down, but the evaporator fan is run for an extended period, forcing relatively warm air over the coil. Whatever ice was there melts and the system can return to it’s regular cycling after the defrost cycle finishes. This can be set to run on timers or in more advanced systems, as necessary using temperature readings. In some installations, it can even be boiled down to a timer which triggers the cycle once every 24 hours and just turns off the refrigeration system for an hour to […]

Read More →

How We Installed a Thermostat

Here at the Procure office, most of what we specialize in is pricing, product hunting, and the general theory of what makes your furnace tick. How’s a thermostat work? It measures temperatures and sends either digital signals or specific voltages over wires to make the system do your bidding. Yesterday, we got to actually trade some theory for practice. Specifically, I got to trade theory for practice. My home thermostat of 20+  years finally croaked.   My Symptoms It was pretty hard to miss that the thermostat had died. As it began getting chilly outside and as the house started to feel more like a meat locker, we followed common sense and set the thermostat. At least, we tried to. On day 1, we pushed the little slider to ‘heat’, and the screen stayed dark. On day 2, we changed the batteries. The screen remained dark. Pressing the buttons really did nothing, but after some bored tinkering and prodding, the circulator pump came to life. Heat restored. How much heat? We didn’t know. The home office was an inferno. Our cats refused to go anywhere near the baseboards they usually love to sprawl against. I put a fan in the window and even mother nature’s frosty 30ºF breeze couldn’t fight off the furnace’s heat. Our thermostat had developed a fever or it was nostalgic for the hot and lazy summer.   Other Symptoms of Failure When your thermostat fails, you […]

Read More →

Oil Burner Ignition

Gas systems need either a hot surface or a pilot light to get started, but not oil systems. Why the difference? It boils down to the fuel being fundementally different. Fuels like propane and natural gas enter the combustion chamber in a gaseous state. Once part of that material is lit on fire, it will conduct the heat and light the entire fuel stream. This doesn’t work for oil.   The Major Difference Oil enters the combustion chamber as a liquid and it requires extreme heat to light. This makes a pilot light nearly pointless, as it would be just as easy to light the main burner as the pilot. A hot surface igniter would be a viable option except it needs to be in the path of the fuel stream, where it would endure the direct-heat of the flame throughout operation. Oil as a fuel source is a completely different beast, unrelated to gas heating. These problems all stem from heating oil’s chemical make up. It’s a cousin of diesel fuel used in over the road trucking, but thicker. It shares some of diesel’s inherent safety. Heating oil and diesel require either extreme heat or extreme pressure. This is why diesel trucks don’t have sparkplugs. At least for an engine’s needs, a spark wouldn’t work well in the long run. They generally remain in a liquid state as well, rather than readily becoming gasses.   A Really Big Spark […]

Read More →

Gas Furnace Ignition

We’ve talked a lot about the safety systems keeping your furnace from burning down the building or blowing up your building. This all begs the question: how do we get the flame started in the first place? It’s actually not a fully straight forward answer, and it varies by fuel source and furnace design.   The Old Fashioned Pilot Light In days long-gone, a furnace needed a constant flame to light it’s burner. This was called a Pilot Light. It was just a tiny, constant little flame like a lit candle. When the burner started, it simply had to turn the gas on and the pilot would ensure that the whole burner lit afterwards. The solution worked well enough, but by modern standards is an incredibly wasteful way to run a furnace. In systems with an always-on pilot light, fuel would always be getting burned, even if there wasn’t heating anything. Overtime, this adds up to hundreds and thousands of gallons of wasted fuel. It certainly worked for a time when we had no better alternatives but it’s a relic in today’s high-efficiency world.   Intermittent Pilots One of the major hurdles of moving on from a pilot was creating enough energy to light the fuel. It takes more than just a spark for ignition, it can take significant voltage. Between the fuel mixture, spark size, spark temperature, and everything else, it’s a difficult ballet to directly, electrically light a […]

Read More →

Measuring the Heat

Have you ever wondered how your heating system knows to turn on? Or to turn off? You could say “the furnace controller tells it to” and “the thermostat tells it to,” but that’s not the whole picture, is it? We need a way to measure the temperature inside the furnace and inside our homes. It has to be durable, reliable, and affordable. It doesn’t have to be precise, but it must be right every time it’s measured.   A Complex Web of Technology There are a staggering number of ways to control a furnace through temperature input. A brief and nowhere near all-inclusive list of techniques include: Gas Expansion Tubes, Bi-Metal Switches, Bi-Metal Coils, Thermocouples Driven by a Pilot-Light, Thermistors, and of course modern IR Temperature Sensors found in your enthusiast-chef’s kitchen. These devices are all in some way sensitive to the heat. Bi-Metal systems expand as temperatures change. Measuring the expansion reads the approximate temperature. Gas Expansion Tubes have an internal change in pressure as temperature changes. The pressure can be used to calculate temperature. Thermocouples generate an electrical current when they’re heated. Measuring the current allows you to determine the temperature. Inside a furnace, they’re often heated directly by the pilot light or burner to read flame temperatures. Infrared Thermometers measure “Blackbody (Wikipedia Link)” radiation, but aren’t all that effective around metals or the air. And lastly, we have the humble Thermistor, which varies it’s resistance based on […]

Read More →