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 →

Carbon Monoxide Detectors

Last week we covered how a draft inducer and it’s attached pressure sensor can help prevent Carbon Monoxide from leaking out of a furnace. This week we’re moving up to the next line of defense: a dedicated Carbon Monoxide Detector. These are often installed in new homes and offices as required by local building codes in most of the United States. Where they’re not installed by construction, they’re usually installed by the facility’s owner as a precaution.   What’s the Big Deal? Carbon Monoxide is one of the deadliest, common compounds in the world. It’s is a colorless, odorless gas that will kill you at the right concentrations. There’s only two ways for someone to know they’ve been exposed to a harmful dose: Use a detector or Recognise the Symptoms before it’s too late. The initial symptoms include headache, dizziness, weakness, vomitting, chest pain, and confusion. In large part, these common symptoms can be attributed to hundreds of other ailments, including the common flu. Greater exposure can lead to passing out, arrhythmia, seizures, and death. Even then, there will be longterm complications, including memory problems, movement disabilities, and fatigue. Most people are not able to detect and react to these symptoms as Carbon Monoxide poisoning before it’s too late. They’re often waived off as a flue or some other lesser problem until it’s too late.   How Do We Detect An Invisible, Colorless, Odorless Gas? While Carbon Monoxide itself is […]

Read More →

What is a Flame Sensor?

If a roll out switch is a master “things have gone horribly wrong, stop the show” switch and thermisters are basically limited to measuring temperature, how do we know the burner is actually making a flame? Sure, the thermister will read heat, but that takes time. Imagine the igniter has failed, it takes maybe 10-40 seconds to register enough heat to confirm a flame. The combustion chamber is now pumped full of a potentially explosive fuel mixture and nothing is happening. We need something much, much faster, we need a flame sensor.   How Not to Detect a Flame The way a person knows something is on fire is usually the bright flames and the fact that sticking their hand near it becomes really painful. This approach doesn’t quite work for a furnace. We could measure the light output, that requires more processing power to interpret the data, some incredibly sensitive hardware to detect the tiniest start of a flame, and it doesn’t work on every fuel type. There are systems that work this way, but it’s a little more expensive. We could measure the temperature, but we run into challenges with making a sensor you can shove in the heart of a flame for years on end without failure. It has been done, but it’s expensive. There are however, laws of physics we can exploit to detect a flame without anywhere near so many challenges. We can detect a […]

Read More →

What is a Rollout Switch?

Your furnace is full of sensors, regulators, switches, and detectors of near everything. There are flame sensors, temperature sensors, pressure switches. That’s a lot of stuff that mostly feed into a controller that operates the furnace as long as it sees all the right readings. That one device is an almost single failure point. The only good way to stay safe is with redundancy. In most cases, these are physical, mechanical safeties which will over-ride every other part of a system and force it to stop cold. Cutting Power on Failure The Roll Out Switch is in simplest terms, a very fancy fuse. Most furnaces will have several of them spread throughout, each tuned to a particularly temperature. One near the burner or heat exchanger may be designed to trip if the furnace exceeds it’s maximum rated operating temperature. Another near the controller board may be set much lower, perhaps around 90 degrees celsius, just shy of when most silicon chips start to fail. Some may rest near the fuel line and manifold, set to extremely low temperatures, in case a leak and fire occurs away from the burner. In the event that any of these switches trip, all power to the furnace is cut. There’s no shutdown process, it just loses all electrical power. If things were going wrong or at risk of going wrong, this usually stops the problem dead in its tracks. A shut down furnace cannot […]

Read More →