The author Warren Toedman has taught Heating and Air Conditioning at Harper College in Palatine, Illinois and has re-written the Heating courses for Refrigeration Service Engineers Society.

(RSES). RSES is one o f the largest training organizations in the USA. Mr. Toedman also owned a Heating, Air Conditioning and Refrigeration contracting business for over 20 years. Mr. Toedman also ran a business that did investigations for the insurance industry for 20 years.

Don’t Be Fooled by “No Breakdown” Furnace Guarantees

You’ve probably seen furnace or air conditioner inspection offers that come with a “No Breakdown Guarantee.” It sounds like a great deal—but before you agree, it’s important to read the fine print and understand what you’re actually getting.

What’s Really Covered?

Some companies use these guarantees as a sales tool. The guarantee might sound reassuring, but often it only covers limited situations—or requires you to buy future services from the same company.

Always ask for the guarantee in writing. A legitimate company should have no problem providing a document that clearly explains what’s covered, what’s not, and how to make a claim if something does go wrong.

What a Real Furnace Inspection Looks Like

A proper furnace inspection takes at least one hour. If the technician just glances at your system and says “everything looks fine,” that’s not a true inspection.

A thorough inspection should include:

Temperature readings
Voltage readings
Current readings
Pressure readings
Timing and performance checks

If you don’t get these readings in your service report, the inspection probably isn’t worth your money.

Be Careful of Sales-Driven Inspections

Unfortunately, some technicians are paid on commission for selling new equipment. If someone tells you your heat exchanger is bad and you “need a new furnace,” don’t rush into it. Get a second opinion first—especially if your system seems to be running fine.

Safety First: Carbon Monoxide Detectors

Your furnace burns fuel to create heat, which means carbon monoxide (CO) can be a danger if the system isn’t venting properly.
Always have a CO detector installed in your home. Follow the manufacturer’s directions for placement, testing, and replacement. A properly working detector is one of the most important safety devices you can own.

Understanding Run Capacitors

If your technician checks the run capacitor on your blower motor, it doesn’t have to match the exact number printed on the label.

Here’s what to know:

Most blower motor capacitors are rated between 5 and 10 MFD (microfarads).
The label includes a tolerance of ±5% or ±10%.
- For example, a 5 MFD capacitor with ±5% tolerance can read between 4.75 and 5.25 MFD and still be within spec.
Newer ECM (electronically commutated) motors don’t use a capacitor at all.

Before You Schedule Your Next Furnace Inspection

On the inspection checklist below, you’ll find a comprehensive list of what a proper furnace inspection should include. Email that list to the company before they arrive so you know exactly what to expect—and what you’re paying for.

Taking a few extra minutes to verify what’s included in your inspection can save you money, prevent unnecessary repairs, and keep your home safe and comfortable all winter long.

Download our FREE checklist for inspections.

Some technicians will try to sell you a new capacitor, even though the unit runs and the capacitor i s with-in tolerance often at a very high price. The contractor list price for a 5 MFD capacitor i s around $10.00. The time t o install the capacitor would be 5 to 15 minutes.

For those who are interested the 36 items on the Inspection Form are explained

Understanding Your Furnace Nameplate Information

The nameplate on your furnace (or nearby labels) lists important details about how your system operates.

Input BTU: This is the amount of heat the furnace burns each hour.
Output BTU: This is how much heat actually gets delivered to your home.
The difference between input and output is the heat lost through the exhaust pipe (also called the flue).

Furnaces with metal exhaust pipes (galvanized flues) are usually around 80% efficient, meaning about 20% of the heat is lost.
Furnaces with PVC exhaust pipes are 90–98% efficient, so only 2–10% of the heat escapes.

Temperature Rise

Older furnaces (made before about 1980) often don’t list the temperature rise on the nameplate. These units sometimes have a limit switch set as high as 200°F.

Newer furnaces (made after 1980) that use an induced draft motor—including both 80% and 90% efficient models—do list the temperature rise. This is the difference between the supply air and return air temperatures, usually around 40–80°F.

Motor and Capacitor Information

The blower motor’s horsepower and amperage may or may not appear on the furnace nameplate. If not, you can usually find it printed on the motor itself—sometimes you’ll need a small mirror on a stick to see it.

The induced draft motor’s amperage is normally listed right on the motor and is easy to spot.

If your technician checks the run capacitor, remember: it doesn’t need to match the exact number printed on it.

Most furnace capacitors are between 5 and 10 MFD (microfarads).
Each has a tolerance of ±5% or ±10%, which means small variations are perfectly fine.
Newer ECM motors don’t use capacitors at all.

Be cautious—some technicians may try to sell you a new capacitor even when yours is still within tolerance and working properly, often at an inflated price.

At supplyhouse.com under the search window enter run capacitor to view various run capacitors. Click on one of he capacitors. Place the Cursor over the capacitor so that you can read the capacitance and the tolerance.

This check is to make sure that the thermostat works properly and is accurate.
If the furnace is an 80% efficient furnace that uses metal pipe to go up through the roof or
connects to a chimney, the flue cap must meet NFPA54 requirements. The flue cap prevents
rain, birds o n other animals from entering the flue. If the flue is restricted it can cause large
amounts of carbon monoxide to be produced at the furnace.
The service person will ask you if you have a carbon monoxide alarm. It is recommended that
the alarm have a digital read out t o indicate the level of carbon monoxide and that the alarm is
installed as per manufacturers instructions. It is recommended o n many alarms that they b e
replaced every 5 to 7 years. Check the instuctions for the carbon monoxide alarm.
This question is t o determine if the rooms in the house heats and cools evenly. Many two-story
homes have significant temperature differences between the first and second floor.
Some homes have high humidity problems in the summer and low humidity problems in the
winter. Some people have allergy problems. There are solutions for all o f these problems.
Some furnaces are connected to the black gas pipe with a flexible connector or a range
connector. Some of the older range connectors can crack or break and cause a significant gas
leak. The proper way to connect the furnace is to use black gas pipe with a black pipe union.
This test is to make sure that there are no gas leaks in the gas piping. An electronic combustible
gas leak detector is much more sensitive than smell. A liquid soap solution is used to detect the
exact location of the leak. Propane and natural gas companies add Ethyl-Mercaptan t o the gas as
an odorant so that if there is a gas leak it can be detected by smell.
Metal flue clearance is important to prevent a fire. Double wall (B-vent) requires a one inch
clearance from wood or combustible.
Single wall metal flue pipe requires 6 inches from wood or combustibles to make sure there is
no fire hazard.
All furnaces require combustion air to support combustion. If if the furnace uses combustion
air from inside of the house or crawl space, NFPA54 has a lot of rules to insure that the furnace
has adequate combustion air. This is t o insure that there is adequate combustion air so that the
furnace does not produce carbon monoxide in the occupied space. This may require two
combustion air pipes from outside or the attic to make sure that the furnace and or water heater
has adequate combustion air. Newer tight houses may require combustion air even if the
furnace is located in a larger basement area. It is recommended that 90% efficient furnaces that
have a combustion air connection use PV pipe to bring combustion air from outside o f the
house. I f the furnace uses combustion air from inside of the house NFPA54 rules require that
all exhaust fans and the clothes drier be operated for a considerable amount of time to make
sure that the furnace has adequate combustion air.
This to make sure that there is not paper, cardboard, Kerosene, gasoline, oil, paint or any other
combustible materials located in the furnace area.
This is a visual check of the heat exchanger to look for rust, cracks and holes. It is necessary to
remove the burners and some welded seams may look like a crack. In older furnaces that have
ribbon burners that are approximately 18 inches long, one way to check the heat exchanger is
to wait for the blower to come on. If the flames move when the furnace blower comes on it i s
likely there are cracks or holes in the heat exchanger. The favorite scam of some
contractor’s is to tell you that you have a crack in the heat exchanger and that you may
die tonight from carbon monoxide. They will tell you that you need a new furnace. If you
have a properly installed carbon monoxide detector (as per manufacturers instructions)
the alarm will sound if there is a dangerous amount of carbon monoxide in the space.
If the heat exchanger has rust the rust should be removed. This consists of brushing and
vacuuming the rust out of the heat exchanger. If there is rust in the heat exchanger i t is likely
that the flue i s not venting properly.
This generally applies to older furnaces with ribbon burners or cast iron boilers with ribbon
burners or cast iron burners. If the burners have rust on them they will be removed and cleaned
with a wire brush and a vacuum cleaner. If there is rust o n the burners it is likely that the flue is
not venting properly. In-shot burners o n newer furnaces generally d o not collect rust.
The induced draft motor may have lint on it, which could cause it to overheat.
This is the induced draft motor ampere on a single stage furnace o r on the high stage of many
two-stage furnaces.
This is the induced draft motor ampere on many two-stage furnaces.
Lint on the blower motor can cause the blower t o shut down or cause i t t o fail pre-masterly do
to overheating. Using compressed air to clean the blower motor makes sure that the blower
motor does not overheat and shut of causing a failure of the heating system. Cleaning the
blower wheel with compressed air, makes sure that the blower moves the proper amount of air
through the furnace and prevents the furnace from shutting off o n the limit switch. If the
furnace shuts off on the limit switch the limit switch will reset and the furnace will operate
until the limit switch shuts off the furnace again. You man not know there is a problem until it
gets really cold outside. I n some cases the lower wheel i s dirty enough that it needs to b e
removed from the furnace and needs to be cleaned with a hose or a pressure washer. This is
not part of the furnace inspection and will b e billed a s a n extra charge.
The ampere reading on the blower motor is a check to make sure that the blower motor is
working correctly. The nameplate amperes listed on the blower motor, is the amperes for the
blower motor on high speed. This is generally the speed used for cooling. The amperes used
for the heating speed is generally less.
On many two-stage furnaces the blower amperes will be less than the blower amperes on the
high heat stage.
If the filter o r filters for the furnace are dirty they should be changed. A dirty filter o r filters
may cause the furnace to shut down on the limit switch do to insufficient airflow. One inch
thick filters should be changed one time per month in most cases.
It is possible that one or more of the ¼ inch quick connects or push on connectors is loose. If
they are loose they should be crimped or replaced. Wire nuts should be checked to make sure
that they are tight. Loose wiring connections can cause the furnace not to work.
Most furnaces use a hot surface ignitor to ignite a gas burner. If the ignitor is pulling less
amperes i t may be near the end of its life. Oversized furnaces will cycle on and off more often
which will reduce the life of the hot surface igniters. Some igniters actually light a pilot, which
lights the main burner. Some furnaces use a spark ignitor to light a main burner..
On older furnaces with a standing pilot which uses a thermocouple a s a safety control, i t is
necessary to hold the knob down for around 3 0 seconds t o make sure that the thermocouple is
hot enough to hold the safety valve open. A t 5 to 8 millivolts the thermocouple will generally
hold the safety valve open.
On older furnaces with a standing pilot which uses a thermocouple as a safety control, after the
pilot is extinguished the safety solenoid should snap shut within 6 0 to 90 seconds. The
thermocouple will generally hold the safety valve open until the millivolts falls t o around 2
millivolts.
On newer furnaces that directly light the burners the safety system should allow a few seconds
for all of the burners to light. The ignitor or spark ignitor lights the first burner and the flame
sensor is located on the last burner. This i s done t o make sure all of the burners light. In order
to check the safety the main gas valve to the furnace is shut off and the time that there is 24
volts on the gas valve terminals is measured. The time should be approximately 3 to 5 seconds.
This is a visual look to make sure the burners light smoothly without a delay. The burners
should light smoothly and the flame should carry over from one burner t o the next burner i n a
smooth manner without a time delay.
The manifold pressure on most single stage natural gas furnaces or two stage furnaces o n high
fire is 3.5 inches of water column pressure. Natural gas furnaces and boilers have a n adjustable
pressure regulator that reduces the gas pressure from around 7 inches of water column pressure
to 3.5 inches of water column pressure. On single stage propane furnaces there is generally not
a pressure regulator for the furnace. The manifold pressure is generally from 10 to 11 inches of
water column pressure..
The manifold pressure on two stage natural gas furnaces varies with the make and model of the
furnace. It is generally around 2.5 inches of water column pressure.
Older furnaces with a draft hood instead of an induced draft motor generally turn the blower
motor on with a n internal furnace thermostat. The thermostat turns the blower o n at around
130 degrees F. Newer furnaces often have a timer that turns the furnace blower on generally
around 30 to 60 seconds after the burners are lit. These controls prevent the furnace from
blowing cold air a t the beginning o f the heat cycle.
Older furnaces with a draft hood instead of an induced draft motor generally turn the blower
motor off with a n internal furnace thermostat. The thermostat turns the blower off generally
around 110 degrees F. Newer furnaces often have a timer that turns the furnace blower off 60
t o 120 seconds after the burners g o off. These controls increase the efficiency o f the furnace by
removing heat from the heat exchanger when the furnace shuts off.
This is the safety control that prevents the furnace from starting a fire. The best way i s t o use a
thermocouple probe with a thermocouple probe temperature meter to measure temperature.
The thermocouple probe should be close to the limit switch sensor. Unhook the common wire
from the blower motor, turn the furnace o n and wait for the limit switch t o shut off the burners.
The temperature when the burners shut off should be close t o the limit switch setting. Another
way to test the limit switch is to measure the time from when the burners g o on t o when the
burners shut off. The time i s approximately 3 to 5 minutes.
Return air temperature i s measured so that the temperature difference across the furnace can be
calculated.
Supply air temperature is measured so that the temperature difference across the furnace can be
calculated.
Supply air temperature minus return air temperature, equal temperature difference across the
furnace. Newer furnaces have an allowable temperature difference range listed on the
nameplate. If the temperature difference is above the listed temperature difference range on the
furnace the furnace likely t o cycle o n and off o f the limit switch. This can b e caused b y a dirty
return air filter, dirty blower wheel, blower wheel running backwards, dirt and lint on the
secondary heat exchanger of a 90% efficient furnace, o r inadequate ductwork.
If the temperature difference is below the listed temperature range on the furnace it is likely
that moisture will condense o n the furnace heat exchanger and will cause rust on the heat exchanger
and cause the heat exchanger to fail. The temperature rise should be no more or no less than the temperature rise listed on
the furnace nameplate.
If the float o n the condensate trap is stuck in he down position condensate water from the
secondary heat exchanger will back u p and cause one of the pressure switches to trip and shut
down the furnace. The furnace may have t o run from 3 0 minutes to 45 minutes for this to
occur. If the furnace shuts down on the pressure switch, it is a good idea to remove the hose
that goes from the heat exchanger to the condensate trap to make sure that the condensate trap
i s working. Remove the hose from the condensate trap. B e careful. If the condensate trap is
not working there be as much as a quart of water that can drain out.
These instructions may include how to install a down-flow furnace o n a combustible floor,
distances from combustibles for the furnace.

What a Real Furnace Inspection Should Include (and What Most Don’t)