Chapter 18 Exercises: How Heating Systems Work

These exercises move from observation and documentation to calculation and decision-making. Some require physical access to your heating system; others ask you to research, calculate, or plan. Do the safety checks before opening any furnace panels.

Exercise 1: Identify Your Heating System

What to do: Locate your home's primary heating system and document it completely.

Find the equipment label (usually inside the cabinet door or on the unit itself). Record: - Manufacturer and model number - Serial number (decode the manufacture year using the manufacturer's website) - Fuel type (gas, oil, propane, electric, heat pump) - BTU output or heating capacity - AFUE rating (if listed) - Date of last service (may be on a sticker from the service company)

Questions to answer: 1. How old is your system? 2. What is its rated AFUE efficiency? 3. Is it a standard or high-efficiency (condensing) system? How can you tell? 4. Based on its age and type, would you classify it as aging, mid-life, or new?

Exercise 2: Observe the Combustion Sequence

Safety note: Observe only — do not touch anything while the system is running.

On a cool day when the furnace will cycle, stand near the furnace and observe a full heat cycle from call to end. Time each phase with your phone: - How long does the inducer pre-purge run before ignition? - How long from ignition to when the main blower starts? - What color is the flame (should be primarily blue)? - How long does the blower run after the burner shuts off?

Questions to answer: 1. Is the flame clean blue, or does it have a significant yellow/orange component? 2. Does the blower delay make sense to you now that you understand why it exists? 3. Did you notice any unusual sounds during the cycle (banging at ignition, rattling, rumbling)?

Exercise 3: The Heat Exchanger Safety Check

What to do: Perform the visual portion of a heat exchanger inspection.

Important: This is observation only. If you see any warning signs, stop and call a professional — do not try to repair anything yourself.

  1. Shut the furnace off at the thermostat and wait 30 minutes for it to cool.
  2. Open the furnace cabinet (most snap open; some have screws).
  3. Using a flashlight, examine the visible portions of the heat exchanger. Look for: - Rust or dark discoloration - Cracks or holes in the metal - Evidence of soot outside the heat exchanger (indicates combustion gas leakage)
  4. Check the area around the burner for soot deposits or discoloration on surrounding surfaces.

Questions to answer: 1. What did you observe? 2. Does your furnace have a CO detector nearby? Test it. 3. When was the last time a technician specifically mentioned inspecting the heat exchanger?

Exercise 4: Calculate Your Heating Fuel Cost

What to do: Using your utility bills from last winter, calculate your actual heating cost per BTU and compare it to other fuel options.

  1. Find last year's gas bills (or oil/propane delivery records) from October through March.
  2. Sum the total fuel cost and total fuel quantity consumed.
  3. Using your furnace's AFUE, calculate the cost per 100,000 BTU (1 therm equivalent) of usable heat delivered: - Formula: Cost per BTU of heat = (Fuel cost per unit × 100,000 BTU/unit) ÷ AFUE - Natural gas: 1 therm = 100,000 BTU; check your gas company's rate per therm - Propane: 1 gallon = 91,500 BTU; calculate from delivery cost per gallon - Electricity (resistance): 1 kWh = 3,412 BTU; 100% efficiency

Questions to answer: 1. What is your actual cost per 100,000 BTU of delivered heat? 2. How does your current fuel compare to alternatives available in your area? 3. If you have a low-AFUE furnace, how much would you save annually at the same fuel usage if you upgraded to a 95% AFUE unit?

Exercise 5: Hot Water Boiler Inspection (if applicable)

If your home has a boiler system:

  1. Locate the system pressure gauge. What is the current cold pressure? (Should be 12–15 PSI.)
  2. Locate the expansion tank. Is it the old style (plain steel) or modern (bladder type)? If old-style steel, has it ever been replaced?
  3. Locate the pressure relief valve. Are there any mineral deposits or staining below it indicating it has dripped?
  4. Check one radiator or baseboard unit. Is it warm throughout its length when the system is running, or cold in spots? (Cold spots indicate trapped air — bleeding needed.)

Exercise 6: Heat Pump Balance Point Observation

If your home has a heat pump:

Over the course of one winter week, record: - Daily low outdoor temperature - Whether the system is running on heat pump or aux/emergency heat (check thermostat display) - Your utility consumption for that day if readable from a smart meter or utility app

Questions to answer: 1. At approximately what outdoor temperature does your system switch from heat pump to aux heat? 2. Is your auxiliary heat electric resistance or gas backup? How does this affect operating cost? 3. Based on your observations, does your heat pump appear to be doing most of the work, or does aux heat run frequently?

Exercise 7: Propane or Oil System Safety Check (if applicable)

For propane or oil-heated homes:

  1. Locate your fuel tank. Record the manufacturer's label: tank capacity and date of manufacture.
  2. Check the tank gauge. What percentage full is it?
  3. For propane: Is the tank on automatic delivery or will-call? If will-call, what is your current ordering threshold?
  4. For oil: When was the tank last inspected? Is it above-ground or below-ground?
  5. Locate the fuel shutoff valve (should be on the supply line between tank and appliance). Make sure you know how to operate it.

Calculate: At your current fuel usage rate and tank level, how many days of fuel do you have? Is that enough buffer for your climate?

Exercise 8: AFUE Upgrade Cost-Benefit Analysis

Scenario: Your 80% AFUE gas furnace is 18 years old. A contractor quotes $3,200 to replace it with a new 96% AFUE condensing unit. Your annual gas heating bill averages $1,400.

Do the math: 1. Estimate current annual cost at 80% AFUE vs. what you'd spend at 96% AFUE. - At 80% AFUE: you pay for 100 units of gas to get 80 units of heat - At 96% AFUE: you pay for 100 units of gas to get 96 units of heat - Savings factor: (96−80)/96 = the percentage reduction in gas needed for the same heat output 2. Calculate annual savings. 3. Calculate simple payback period for the $3,200 investment. 4. If the new furnace lasts 20 years, what is the total lifetime savings?

Questions to answer: 1. Does the upgrade make financial sense? What factors might change your conclusion? 2. What non-financial factors (comfort, reliability, safety) might affect the decision? 3. Would utility rebates or federal tax credits (check current offerings) change the payback period?

Exercise 9: Electric Heat Spot-Check

If your home has any electric baseboard or radiant heat:

  1. Locate each electric baseboard unit. Check: are there any objects stored against the heater? (Fire hazard — clear 12 inches minimum.)
  2. Turn the individual thermostat to maximum and confirm the unit heats (feel warmth along the length within 5 minutes).
  3. Using the formula (watts × hours ÷ 1,000 = kWh), estimate the daily operating cost of one unit at your electricity rate: - A typical 1,500-watt baseboard running 8 hours/day: 1,500 × 8 ÷ 1,000 = 12 kWh - At $0.15/kWh: $1.80/day

Questions to answer: 1. If this unit were replaced by a mini-split heat pump with COP of 3.0, what would the equivalent daily cost be? 2. Does the spot-heating application (a room you use occasionally) justify the higher operating cost of electric resistance heat?

Exercise 10: Annual Service Scheduling

What to do: Research and schedule your annual heating system inspection.

  1. Find a licensed HVAC contractor in your area (check state licensing boards, ACCA-member contractors, or your utility's list of approved contractors).
  2. Call two or three and ask specifically: does your annual inspection include opening access panels to visually inspect the heat exchanger? (The answer tells you the quality of their inspection.)
  3. Ask for a written scope of work that lists every item covered in the inspection.
  4. Schedule the inspection before the heating season (September/October is ideal).

Final reflection: Write a one-paragraph summary of your heating system's current condition, any concerns you identified in these exercises, and the maintenance items you've scheduled or plan to address.