The Client Who Wants a Number, Not a Lecture
After a full audit - blower door 3,400 CFM50, duct leakage 12%, attic R-9, 1995 furnace at 80% AFUE, and a modeled savings of 180 therms/year for a $6,500 attic air-sealing and insulation package - the homeowner says: "Just tell me the payback. If it's under five years I'll do it." Gas is $1.10/therm. The client also mentions they may sell the house in two years. The auditor's model has a ±20% uncertainty band, and the client has already been told by a contractor that "insulation pays for itself in three years."
1. Compute the simple payback and explain honestly how uncertainty and the two-year horizon change the answer.
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Simple payback: 180 therms × $1.10/therm = $198/year. $6,500 ÷ $198 = about 33 years. That is far outside the client's five-year threshold, and it is far outside the contractor's "three years" claim.
Uncertainty: the model carries ±20%, so annual savings are roughly $158-$238, and payback ranges from about 27 to 41 years. Even the optimistic end does not approach five years. The contractor's three-year claim would require roughly $2,200/year in savings - about 2,000 therms - which is more than the house uses. The claim is not credible.
Two-year horizon: if the client sells in two years, they recover about $400 in energy savings against a $6,500 investment. The rest must be recovered through resale value or comfort, which are real but not guaranteed and not captured in a simple payback. A buyer may value a documented, verified improvement, but the auditor should not promise it.
Honest answer: the payback is not under five years; it is roughly three decades on energy alone. The case for the work rests on comfort, durability (attic moisture and ice dams), and resale documentation, not on energy payback.
2. How would you present this to the client so the conversation stays honest and useful, and what alternatives would you offer?
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Presentation: lead with the number they asked for - "about 33 years on energy savings alone, with a range of 27-41 years" - then explain why the contractor's three-year figure cannot be right (it would require more savings than the house's total gas use). Do not soften the number; the client asked for it and will make a worse decision if given a comfortable fiction.
Then reframe: the value is comfort, moisture control, and durability, plus documented resale value. Offer to write a short measure report the client can hand to a buyer.
Alternatives to offer:
- Phased, lower-cost air sealing only (often the highest-return piece) with a post-work blower door to verify.
- Duct sealing if the 12% leakage is to unconditioned space - usually cheaper per unit saved than attic insulation.
- A smaller insulation package if the client wants to spend less now.
- Defer if the client is truly selling in two years and values cash over comfort - that is a legitimate choice.
Close by asking what they value most: monthly cash, comfort, or resale. The scope should follow that answer, not the contractor's claim.