What You’ll Learn
What is furnace temperature rise, and why does it matter?
Temperature rise measures how much the furnace heats the air as it passes through the system.
A reading outside the manufacturer’s range can indicate airflow or equipment problems.
In this blog:
Donna had tried everything.
She turned the thermostat up. She checked the register in her bedroom. She even wondered if she needed to rearrange the furniture.
Still, while the living room stayed comfortable, her bedroom felt like winter had made it through the front door.
Her thermostat said 70°F, so why wasn’t the room?
When a Kauffman Gas technician sees uneven heating like this, they may look at something most homeowners have never heard of: temperature rise.
What Temperature Rise Tells You About Your Furnace
Temperature rise is the difference between the temperature of the air entering your furnace and the temperature of the heated air leaving it.
For example, if 65°F air enters the furnace and 115°F air leaves it, the temperature rise is 50°F.
Every furnace has a manufacturer-specified temperature rise range. That range tells technicians how much the air should increase in temperature as it passes through the furnace when the system is operating properly.
The goal isn’t simply to make the air as hot as possible. The furnace needs to produce heat while moving the right amount of air through the system.
If airflow is restricted or another component isn’t operating correctly, the temperature rise can fall outside the manufacturer’s recommended range.
That can eventually show up where homeowners notice it most: inside the house.
A furnace might be running, but if the system isn’t moving and distributing air properly, some rooms may stay colder than others, airflow may feel weak, or the furnace may run longer than expected.
Temperature rise gives our techs a snapshot of how the furnace and airflow system are working together.
It isn’t a standalone diagnosis. Instead, it’s one of the measurements that can help a technician determine whether something deserves a closer look.
Why Temperature Rise Matters to Your Furnace
A furnace is designed to operate within a specific range of conditions. It needs to produce heat, transfer that heat into the air, and move that heated air through the ductwork.
Temperature rise helps technicians determine whether those processes are happening within the range specified by the manufacturer.
When airflow is restricted, for example, less air may move across the heat exchanger. That can cause the air passing through the furnace to become hotter than intended, increasing temperature rise. If the reading falls outside the manufacturer’s specifications, the furnace may not be operating as efficiently or reliably as it should.
And the effects can extend beyond uneven heating. Excessive temperature caused by restricted airflow can cause the furnace’s high-limit safety control to shut the burner off to prevent overheating. If that happens repeatedly, the furnace may cycle abnormally, struggle to maintain a comfortable temperature, and experience additional stress on its components.
Over time, unresolved temperature and airflow problems can contribute to:
- Reduced efficiency
- Repeated safety-limit trips
- Increased component stress and premature wear
- Uneven heating and abnormal cycling
- Shortened equipment life
- Unexpected breakdowns
A temperature-rise reading doesn’t necessarily mean the furnace is failing. It can be an early clue that something isn’t operating as intended.
That’s why professional maintenance matters even when the furnace appears to be working normally. A technician can identify developing airflow or performance problems while there’s still an opportunity to address them—rather than waiting until they become a winter emergency.
A furnace tune-up isn’t just about making sure the furnace turns on. We’re checking how the equipment is actually operating. Temperature rise is one measurement that can help identify an issue before it affects your comfort or turns into a larger repair.
What Causes Incorrect Temperature Rise
A temperature-rise reading outside the manufacturer’s specified range can have several causes.
That’s why technicians use the measurement as a starting point for further investigation.
A Dirty or Restrictive Air Filter
A clogged filter can restrict the amount of air moving through the furnace.
When less air moves through the system, the furnace may transfer more heat into a smaller amount of air, potentially causing the temperature rise to climb too high.
That’s one reason changing your filter isn’t just about keeping dust out of the home. Proper airflow is also important to furnace performance.
Blocked or Restricted Ductwork
Your furnace can produce plenty of heat, but that heat still needs somewhere to go.
Blocked, damaged, undersized, or restricted ductwork can interfere with airflow through the system. The result may be a temperature rise outside the furnace’s expected range and rooms that don’t receive the amount of heated air they should.
This can be particularly noticeable in homes where one room consistently feels colder than the rest.
An Oversized Furnace
A furnace that is too large for the home can create performance problems of its own.
An oversized furnace may heat the home quickly and shut off before the system has properly distributed heat throughout the space. Frequent cycling can affect comfort and put additional wear on the equipment.
Proper furnace sizing is therefore about more than having enough heating capacity. The furnace needs to be appropriately matched to the home and its airflow system.
Blower or Airflow Problems
The blower is responsible for moving heated air through the home’s ductwork.
If the blower isn’t operating properly, or if airflow settings aren’t correctly adjusted, the amount of air moving through the furnace can change.
That can affect temperature rise and the overall performance of the heating system.
How Technicians Measure Temperature Rise
Temperature rise is relatively simple to calculate, but the information it provides can be valuable.
During a furnace tune-up, a technician measures:
1. The temperature of the air entering the furnace
This is the return-air temperature before the furnace heats it.
2. The temperature of the heated air leaving the furnace
This is measured after the air has passed through the furnace.
3. The difference between those temperatures
The technician measures the temperature of the return air—the air being pulled from your home—and the supply air—the heated air leaving the furnace and being sent back through your ductwork.
The difference between those temperatures is the furnace’s temperature rise.
For example:
115°F supply air − 65°F return air = 50°F temperature rise
The technician then compares that measurement with the temperature-rise range specified by the furnace manufacturer.
If the number falls outside that range, the technician can investigate potential causes, such as a restricted filter, ductwork issues, blower problems, or other airflow concerns.
It’s important to remember that there isn’t one temperature-rise number that’s right for every furnace. The manufacturer’s specifications are what matter.
The number doesn’t tell us exactly what’s wrong. It tells us where to start looking.
That’s why temperature rise is most useful when it’s considered alongside the rest of the furnace inspection.
Don’t Wait for Uneven Heat—Contact Kauffman Gas for Professional Furnace Maintenance
If one room is always colder than the rest of your home, or your furnace seems to run constantly without keeping the house comfortable, don’t automatically assume it’s simply an old furnace.
Temperature rise gives technicians one more way to understand what’s happening inside the furnace.
During professional maintenance, Kauffman Gas technicians can evaluate temperature rise alongside the furnace’s other operating conditions and look for issues that could affect comfort, efficiency, and equipment life.
Contact Kauffman Gas to schedule your furnace maintenance and make sure your heating system is ready for the season ahead.
FAQs
What is a normal furnace temperature rise?
There isn’t one temperature-rise number that’s considered normal for every furnace. The correct range depends on the specific equipment, so technicians compare the measured temperature rise with the manufacturer’s specifications.
How is furnace temperature rise measured?
A technician measures the temperature of the air entering the furnace and the temperature of the heated air leaving it. The difference between those two readings is the furnace’s temperature rise.
What causes a furnace temperature rise to be too high?
Restricted airflow is a common cause. A dirty filter, blocked ductwork, closed registers, blower problems, or other airflow restrictions can prevent enough air from moving through the furnace.
Can temperature rise affect how warm my home feels?
Yes. Problems with airflow and furnace operation can contribute to uneven heating, weak airflow, rooms that remain cold, or a furnace that runs longer than expected.
Does a high temperature rise mean my furnace is broken?
Not necessarily. An incorrect reading is a reason for a technician to investigate. The cause could be something as simple as a restricted filter or may involve airflow, ductwork, blower operation, or another component.
Why does temperature rise matter during a furnace tune-up?
It gives technicians useful information about how the furnace and airflow system are operating. Comparing the measurement with the manufacturer’s specifications can help identify problems before they lead to comfort issues or equipment damage.