Chapter 20 Exercises: Ductwork, Airflow, and Ventilation

These exercises ask you to investigate, measure, and evaluate the duct systems and ventilation in your own home. Many of the problems described in this chapter are invisible and silent — the exercises are designed to make them visible.

Exercise 1: Map Your Duct System

What to do: Create a simple sketch of your home's duct system.

Walk through each room and note: - Supply register locations (mark S on sketch) - Return grille locations (mark R on sketch) - Approximate register/grille sizes (measure with a tape measure) - Whether each supply register has an adjustable damper (a lever or wheel to open/close)

Then go to your basement, attic, or crawlspace (wherever ducts are accessible) and trace what you can see. Note: - Main trunk duct size and material (sheet metal, flex, fiberboard) - Any visible disconnections or damage - Condition of duct insulation - Any joints that appear to be sealed with nothing (no mastic, no tape)

Questions to answer: 1. How many supply registers vs. return grilles does your system have? Are they balanced (roughly one return for every 2–3 supply registers, or a large central return)? 2. Are there any rooms with supply registers but no apparent return path? 3. Can you identify what material your main trunk duct is made of?

Exercise 2: Airflow Comparison Test

What to do: Measure and compare airflow at every supply register in the house.

Equipment needed: A tissue, a small piece of paper, or an inexpensive anemometer (available for $20–40 online).

With the system running on heat or cool, hold a tissue at each supply register. Rate airflow on a simple scale: strong, moderate, weak, or barely perceptible. Record each room.

Analysis: 1. Which rooms have the weakest airflow? 2. Is there a pattern? (Rooms farthest from the air handler? Rooms on upper floors?) 3. For the weakest register, check the duct path from the air handler. Is the flex duct run very long, kinked, or sagging?

Follow-up action: If you find a room with notably weak airflow, check whether the problem is a damper that's partially closed, a kinked flex duct, or a disconnected section.

Exercise 3: Duct Leak Inspection

What to do: Inspect accessible ducts for leakage during system operation.

Safety note: Stay clear of moving parts and don't reach into any openings.

With the system running: 1. Put your hand near every accessible duct joint (where sections connect, where flexible duct meets a sheet metal fitting, where the trunk connects to the air handler). 2. Do you feel moving air escaping from any joints? 3. Do the same at every supply boot connection (where the duct terminates at the floor, ceiling, or wall register). Feel around the edges of the boot where it meets the framing — this is a very common leak point.

Mark any leaks you find with a piece of painter's tape so you can find them again when it's time to seal.

Seal what you find: Purchase UL 181 duct mastic (a thick paste; apply with a brush or gloved hand) or UL 181 aluminum foil tape (not regular duct tape). Seal every joint you found leaking. This is the highest-ROI DIY project in this chapter.

Exercise 4: Bathroom Fan Termination Check

This is one of the most important checks in this chapter.

  1. Locate every bathroom exhaust fan in your home.
  2. Turn on each fan and go to the attic (or wherever the duct would terminate). Can you feel or hear air movement in the attic? Can you see or feel a flex duct that disappears into insulation without connecting to a proper roof or wall cap?
  3. Go outside and look for exhaust termination caps on the roof and exterior walls near bathroom locations.

If you find a fan ducted to the attic (not terminated outside): - This is a code violation and causes moisture damage. - Correcting it requires routing insulated flex duct from the fan housing to a roof cap or sidewall cap. - Get a quote from a contractor if you're not comfortable with attic work and roof penetrations.

Document: For each bathroom, record whether the fan terminates properly outside or in the attic.

Exercise 5: Range Hood Verification

What to do: Verify your range hood operates correctly and is vented to outside (if it should be).

  1. Turn on the range hood fan to its highest setting.
  2. Hold a tissue near the hood opening — does it draw strongly toward the hood?
  3. Go outside and look for the exterior exhaust cap. Hold your hand near it while the fan runs — do you feel exhaust air coming out?
  4. If you can't find an exterior cap, your hood may be recirculating. Check the owner's manual or look inside the hood for charcoal filters (recirculating hoods have them; vented hoods do not).

If your range hood recirculates: - Recirculating hoods remove grease and odor but return moisture and combustion gases to the kitchen. - Assess whether exterior venting is possible (through a cabinet, exterior wall, or ceiling/roof). - If not, ensure charcoal filters are replaced per manufacturer schedule.

Exercise 6: Calculate Your Duct Leakage Cost

Estimate-based exercise:

Using the typical range from Section 20.3 (20–30% leakage in typical homes), estimate what duct leakage is costing you.

  1. Find your annual total HVAC cost from utility bills (heating + cooling months).
  2. Apply 25% as a middle estimate of leakage losses. - Annual duct leakage waste = Annual HVAC cost × 0.25
  3. A professional duct sealing job costs approximately $1,500–2,500.
  4. Calculate simple payback: Sealing cost ÷ Annual waste = years to payback

Question: Does the payback make duct sealing cost-effective? How does it compare to other home improvement investments you've considered?

Bonus: If your utility offers a free or subsidized energy audit with duct testing, schedule one to get measured data rather than estimates.

Exercise 7: Return Air Pressure Test

Test for rooms with inadequate return air:

  1. Close all interior doors in the house that lead to rooms without dedicated return grilles.
  2. Run the HVAC system.
  3. With a door closed, slide a piece of paper under it. Does it move — either being pushed out from the room (pressurized by supply air with nowhere to go) or being drawn in?
  4. Open the door and observe: does air visibly rush in or out?

If rooms clearly pressurize with the door closed: Those rooms need better return air paths — transfer grilles, jump ducts, or undercut doors. Pressurized rooms push conditioned air into walls and the attic, wasting energy and potentially causing moisture problems.

Exercise 8: Attic Ventilation Inspection

What to do: Evaluate your attic's ventilation system.

  1. On a cool day, open the attic hatch and spend a few minutes observing.
  2. Can you see daylight from soffit vents? (Have a helper shine a flashlight in from outside if needed.)
  3. Is there a ridge vent along the roof peak?
  4. Are there rafter baffles (cardboard or foam channels) visible at the eaves, keeping insulation from blocking the soffit vent airflow?
  5. Is there any visible moisture staining or mold on the roof sheathing (the plywood on the underside of the roof)?
  6. Are any bathroom exhaust ducts terminating in the attic?

Questions to answer: 1. Does the attic appear to have adequate ventilation (soffit + ridge)? 2. Are there any signs of past or current moisture problems? 3. Are bathroom fans properly terminated outside?

Exercise 9: Evaluate Your Crawlspace (if applicable)

If your home has a crawlspace:

  1. Open the crawlspace access and observe from outside if you're not comfortable going in (wear a respirator if you enter — fiberglass, mold, and rodent debris may be present).
  2. Is there a vapor barrier on the ground? Is it intact?
  3. Are there foundation vents (usually rectangular grilles low on the foundation walls)?
  4. Is the crawlspace vented (traditional) or encapsulated (sealed, conditioned)?
  5. Are there any ducts running in the crawlspace? Are they intact and insulated?
  6. Do you see any moisture staining, standing water, efflorescence (white mineral deposits), or visible mold on wood framing?

Questions to answer: 1. Based on what you observed, does your crawlspace appear to be adequately protected from moisture? 2. If you have a vented crawlspace, does it show signs that the traditional vented approach is creating moisture problems? 3. If there are uninsulated or poorly-insulated ducts in the crawlspace, what does that mean for your HVAC efficiency?

Exercise 10: HRV/ERV Research and Decision

Research task:

  1. Find your home's approximate ACH50 from a past energy audit, a real estate disclosure, or a blower door test. If you don't have this data, use your home's construction era as a proxy: - Pre-1980: likely 12–20+ ACH50 - 1980–2000: likely 7–12 ACH50 - 2000–2015: likely 4–8 ACH50 - Post-2015 new construction: likely 2–5 ACH50

  2. If your home is below 5 ACH50, research whether mechanical ventilation is warranted.

  3. Look up HRV and ERV units from two manufacturers (Panasonic, Broan, Lifebreath, or Renewaire are common residential brands). For a 2,000 sq ft, 3-bedroom home, find a unit rated for 60–80 CFM continuous.

  4. Get a contractor quote for HRV/ERV installation if your home is tight enough to benefit.

Reflection: Based on your research, does your home's airtightness level call for mechanical ventilation? What are the options in your price range?