The secondary heat exchanger is where the flue gas undergoes further heat exchange and water vapor forms. After exiting the primary heat exchanger, the burning gas proceeds to the secondary heat exchanger. As water is changed from a vapor to a liquid, it releases more heat into the secondary heat exchanger.
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Contents

What is the function of the secondary heat exchanger?

As the combustion exhaust leaves the primary heat exchanger, it travels into a secondary heat exchanger where more heat is released from the flue gas and water vapor begins to form.

How do I know if my secondary heat exchanger is clogged?

  1. The condensate in your condensate drain pan is brown or black. …
  2. Your carbon monoxide alarm goes off. …
  3. A Pungent Odor. …
  4. Water Leaking from the Furnace.
What does the secondary heat exchanger do in a condensing furnace?

With a condensing furnace, on the other hand, the combustion exhaust gases are also passed through a secondary heat exchanger that absorbs much of the remaining heat from the gases. As the gases cool, they condense to form water and carbon dioxide (which together form carbonic acid).

How does a heat exchanger works?

Heat exchangers, metal shells and tubes, work by transferring heat from one place to another. … The hot flue gas heats the metal as the gas makes its way to the exhaust outlet of the furnace. As this is happening, the hot metal heats the air circulating over the exterior of the heat exchanger.

How does a heat exchanger work HVAC?

The heat exchanger uses the combustion gases to warm the air, which is then distributed around the home. Exhaust gases from the combustion process are released through the flue to the outside of the home.

Can I run my furnace with a cracked heat exchanger?

If it is your heat exchanger, you cannot run your furnace, even if it seems to be running fine. The gases will continue to seep into your home’s air. Many companies, upon finding a cracked heat exchanger, will shut your furnace down so you cannot run it.

What are the symptoms of a bad heat exchanger?

  • Strange smells. A malfunctioning heat exchanger will often create an unpleasant and strong odor that smells similar to formaldehyde.
  • Soot Build-up. …
  • Corrosion & Cracks. …
  • Change in the flame appearance. …
  • Audible Sounds. …
  • Presence of Carbon Monoxide.
How does a heat exchanger get blocked?

Central heating sludge is another type of debris that can affect a boiler heat exchanger. … Heating sludge is the combined build-up of rust and dirt breaking off from copper pipes, joints, radiators, and towel rails. This gooey mess creates blockages throughout the heating system, and may cause a blocked heat exchanger.

How much does it cost to replace a secondary heat exchanger?

The cost of replacing a heat exchanger ranges from $2,000 to $3,500. Replacing your furnace’s heat exchanger would be a good route to take if your furnace is fairly new. However, it is not worth spending your money on replacing your heat exchanger when it is near the end of its life span, which is ten years or more.

What would cause a fan switch to close?

The switch’s sensor becomes dirty and stops working correctly. The furnace filter is clogged and raises the temperature within the plenum prematurely, tripping the sensor. The blower motor stops working and overheats. … These may cause the fan limit switch to stop working properly.

What causes soot buildup in the heat exchanger and vent?

Soot Build-Up Soot develops due to accumulations of carbon within the furnace. This is usually the case when the furnace is not clean and completely burning fuel, as the result of a poorly adjusted burner or a cracked heat exchanger.

How much does a furnace cost for a 1500 square foot house?

For example, a 700- to 1,500-square-foot home will require a BTU rating between 40,000 and 60,000, which will cost between $2,000 and $3,000. A furnace for a home ranging in size from 2,000 and 5,000 square feet will need between 125,000 and 150,000 BTUs and will cost in the neighborhood of $3,300 to $6,500.

Can a heat exchanger be cleaned?

Cleaning-In-Place (CIP) equipment can clean plate heat exchangers without disassembly. CIP is a combination of time, temperature and concentration. CIP provides both chemical and mechanical cleaning to the heat exchanger. If system configuration prohibits CIP, operators must perform manual cleaning.

How often should a heat exchanger be cleaned?

The association recommends reducing fuel costs by regularly cleaning heat exchangers to prevent fouling, which is often caused by a dirty, malfunctioning burner. Inspect heat exchangers at least once per year and clean them when they look dirty. Inefficient heat exchange is caused by scale and sediment buildup.

How does a heat exchanger work in a combi boiler?

How does a combi boiler heat exchanger work? A boiler works by using hot gas to heat water – and a heat exchanger is what allows this to happen. As the gas is heated, it begins to rise. When it rises, it reaches the heat exchanger and is pushed through the coiled pipe.

How does a heat exchanger work in a heat pump?

An air source heat pump has two heat exchangers. … A coil of tubing filled with refrigerant, it uses the principle of heat transfer to coax thermal energy from the air. Since the space inside the coil is filled with a liquid that is cooler than the surrounding air, thermal energy is drawn into the coil.

Does a cracked heat exchanger always leak carbon monoxide?

A furnace with a cracked heat exchanger will definitely produce carbon monoxide and poses an immediate danger”. … If combustion gasses could move through a crack in a heat exchanger to the indoor air stream, it would defy the laws of physics. (See the cautionary note about 90% units.)

Can a cracked heat exchanger cause a fire?

Carbon monoxide poisoning is not the only possible danger a cracked heat exchanger presents. If combustible gas builds up in your heating unit and is released into your home through a fracture, it can lead to a potentially deadly furnace fire.

How does a heat exchanger crack?

What is the cause of heat exchanger cracks? Overheating causes nearly all premature heat exchanger cracks. When a furnace cannot get enough airflow, the heat exchanger overheats and suffers excess stress from expansion and contraction. Over time, the heat stress causes cracks near weak areas such as bends or welds.

Is it worth replacing heat exchanger?

If your heat exchanger is cracked, your furnace is probably nearing the end of its life (18-20 years). If that’s the case, then it’s usually not worth the money to replace the heat exchanger. No matter who you ask, replacing a heat exchanger will be expensive. … Heat pumps can heat and cool your home.

How do you remove a blockage from a heating system?

  1. Step 1 – Leave the Heating To Cool Down.
  2. Step 2 – Turn off Thermostatic and Lockshield Radiator Valves.
  3. Step 3 – Disconnect Valves from Each Radiator.
  4. Step 4 – Open the Bleed Valve on the Radiator Using a Bleed Key.
  5. Step 5 – Tip Out Any Loose Heating Sludge.
How do I descale my heating system?

Fill it further with water so the water passes the feed connection. Turn on the system and wait for a few of hours (4 or so) to complete the descaling process. Turn on the hot taps every 15 to 30 minutes so hot water runs through the whole system. Flush the system with cold water as well.

Can you replace just the heat exchanger in a furnace?

If parts and labor are still under warranty, you can probably replace just the exchanger for now. If you’re covered for parts but not labor, you can further discuss the pros and cons with your HVAC professional.

How long do heat exchangers last?

In most cases, the heat exchanger determines how long your furnace will last. The heat exchanger is responsible for heating the air that circulates through your home in the winter. Heat exchangers usually last about 15 years. If you invest in maintenance, yours might even last 20.

How long should a furnace last?

A well-maintained furnace can last at least 15 to 20 years, but completing annual maintenance and being diligent with repairs can extend its life even longer.

At what temperature does the fan limit normally closed?

An adjustable fan-limit controller typically is designed for furnaces operating at temperatures from 100°F to 250°F, has a FAN OFF lower limit that can be adjusted from 50°F to 200°F, a FAN ON switch adjustable from 65°F to 215°F and a fan HIGH LIMIT stop set at 200°F.

Why is my furnace fan not turning off?

If your furnace fan won’t turn off, you most likely have one of these 3 problems: Your furnace fan limit switch is set to “manual override” The fan limit switch is faulty and needs to be replaced. There’s a problem in your thermostat wiring.

Why does the fan run when thermostat is off?

Over time, relay switches can become stuck or damaged, preventing the thermostat from communicating with the fan. Essentially, this means that the fan isn’t receiving the commands you’re relaying to the thermostat. So even if you turn your AC off, the fan will continue to run.

Why is my furnace blowing out soot?

Soot is the result of incomplete combustion, meaning that your furnace isn’t burning the gas properly or efficiently. Soot can be deposited on the heat exchanger, acting as an insulating barrier. … Your furnace’s heat exchanger may be cracked, which is what’s allowing the soot to escape into your home’s air vents.

Why is there black soot in my house?

What Causes Black Soot? Almost all household black soot comes from scented candles. Oils in candles don’t burn completely, the oil enters the air and turns into black soot. … Other sources of black soot in the home can come from kerosene lamps or dust brought into the home if a coal mine is located nearby.

What does it mean when black smoke comes out of your chimney?

If you see a lot of black smoke, it’s a sign you’re burning something toxic. a light colored smoke means your fire isn’t burning efficiently and you need to adjust your air intake. … A small, hot fire is the most efficient, burning volatile gases quickly which means better air quality.

Can a furnace be too big for a house?

Having a furnace that’s too big for your space is extremely inefficient. There are two simple signs that indicate that your furnace is most likely oversized: Your furnace runs for a short period of time before shutting off. Your home has uncomfortable hot and cold rooms.

Is it cheaper to replace furnace and AC together?

While it is always necessary to replace both air conditioning components at the same time (in a split system), it’s not always necessary to replace both AC components and the furnace. … Adding a furnace during your air conditioner replacement will cost a lot less, around $1,000 to $3,000.

Should I replace my 25 year old furnace?

Age of your Furnace If your furnace is pushing 25 years or more, it’s probably nearing the end of it’s effective lifespan. … You might choose to replace a 15 year old furnace, or it could last more than 30 years.