Open planning model · version 1.0
This is the working model behind the site’s three planning tools. It publishes the starting bands, multipliers, adders, scoring rules, rounding, limitations, and worked examples so a reader can reproduce a result without trusting a hidden formula.
Purpose and limits
Residential HVAC prices are not published in one complete national database. A contractor’s total combines equipment, local labor, company overhead, permit and inspection requirements, design work, access, electrical or fuel work, ducts, controls, commissioning, warranty obligations, and risk. A precise browser result would hide that uncertainty instead of helping a homeowner manage it.
The model therefore begins with broad editorial bands for recognizable project configurations and adjusts them only for variables the user can describe before an on-site visit. The ranges are intentionally wide. They are useful for building a contingency, spotting missing scope, and asking why local proposals differ. They are not evidence that a local contractor is overcharging or undercharging.
Capacity screens are also deliberately rough. Square footage cannot replace a Manual J calculation because climate, orientation, insulation, air leakage, windows, internal loads, ventilation, ducts, and design temperatures change the load. The model shows when a proposal deserves a documented sizing explanation; it does not select equipment.
Model 01
Base band × size factor × efficiency factor × labor factor + duct allowance.
| Configuration | Low | High | Scope represented |
|---|---|---|---|
| Central AC + gas furnace | $8,500 | $15,500 | Matched outdoor AC, indoor coil, and gas furnace. |
| Ducted heat pump | $9,500 | $18,000 | All-electric heating and cooling with standard air handler. |
| Dual-fuel heat pump | $12,000 | $23,000 | Heat pump paired with a gas furnace for backup heat. |
| Packaged HVAC system | $8,000 | $15,000 | Single outdoor cabinet; common in some warmer regions. |
The model uses 0.75 + square feet ÷ 7,200, capped between 0.86 and 1.32. This is a cost adjustment—not a load calculation. It allows a 3,500-square-foot project to carry more equipment and labor allowance than an 800-square-foot project without claiming that floor area determines tons.
Entry equipment uses 1.00, enhanced efficiency 1.12, and premium or variable-speed equipment 1.25. Labor-market factors are 0.90, 1.00, and 1.18. These factors widen a planning scenario; they do not quote a specific brand or ZIP code.
Keeping tested ducts adds $0. Sealing or sectional repair adds $1,500–$4,500; substantial replacement adds $4,500–$12,000. Access, materials, fire or smoke requirements, and redesign can move real work outside the allowance.
Model 02
First-zone band + added zones, then area and equipment factors, access, and electrical work.
| Indoor-unit style | First zone | Each added zone |
|---|---|---|
| Wall-mounted heads | $4,000–$7,500 | $2,500–$4,500 |
| Mix of wall and compact heads | $5,000–$8,500 | $3,000–$5,200 |
| Ceiling cassettes / concealed ducts | $6,000–$10,500 | $3,500–$6,000 |
The area factor starts at 0.90 and increases after 600 square feet, capped at 1.28. Standard equipment uses 1.00, enhanced 1.12, and cold-climate or premium equipment 1.22. Area is a cost signal only; the capacity screen remains a broad 18–30 BTU/h per square foot to make its uncertainty visible.
Simple accessible runs add $0; mixed access or longer runs add $1,000–$3,000; difficult access or finish repair adds $3,000–$8,000. The quote should state line length, routing, condensate, lifting, penetrations, and finish responsibility.
A suitable existing circuit adds $0. A new circuit and disconnect add $500–$1,800; possible panel or service work adds $2,000–$5,500. A licensed electrician must confirm capacity and code requirements.
Model 03
A disclosed score organizes evidence; it does not predict failure or remaining life.
| Factor | Maximum weight | Why it matters |
|---|---|---|
| Age | 3 points | Older equipment raises the relevance of another near-term major failure, but age alone never forces replacement. |
| Repair share | 3 points | The quote is divided by the midpoint of a broad replacement band for the selected system. |
| Other repairs | 2 points | Repeated repairs weaken the assumption that today’s repair ends the spending cycle. |
| Comfort and reliability | 2 points | Uneven conditions or repeated shutdowns may indicate a design or system problem beyond one part. |
| Energy-use pattern | 1.5 points | A sharp unexplained change deserves diagnosis; weather-normalized utility data is stronger than one bill. |
| Warranty status | 0.5 point | Substantial coverage can change the household cost even when the technical repair is the same. |
The inputs do not show a strong replacement signal. Confirm diagnosis, coverage, and the repair guarantee before authorizing work.
The tradeoff is close enough to justify a second diagnosis and comparable replacement scopes, including defects each proposal corrects.
Several inputs reduce the value of a major repair. Replacement still needs correct design, total financing cost, and a defined commissioning plan.
The calculator uses replacement bands of Central AC + furnace $8,500–$15,500; Ducted heat pump $9,500–$18,000; Furnace only $4,500–$9,500; Single-zone mini-split $4,000–$7,500. Safety findings override the score. A cracked heat exchanger, combustion concern, electrical hazard, or refrigerant exposure belongs with qualified professionals and applicable emergency guidance—not a cost formula.
Evidence standard
Technical and program claims are checked first against government agencies, recognized standards organizations, official program administrators, utilities, and manufacturer documentation. Examples include federal efficiency terminology, tax instructions, refrigerant rules, equipment performance data, and the role of Manual J, Manual S, and quality installation practices.
The dollar bands and adjustment factors on this page are editorial planning assumptions. They are not government statistics, scraped contractor bids, or a proprietary real-time price feed. Publishing them here makes that distinction auditable. We change them only as a versioned model release, then check that the same constants power the live tools and worked examples.
Before publication, we test calculator boundaries, reproduce the examples, check that low results remain below high results, review safety wording, and verify every linked source is relevant to the claim around it. We do not invent professional review, field tests, contractor interviews, owner experience, or local prices.
Change log
Published all base bands, multipliers, adders, scoring rules, formulas, and two reproducible cost examples. Centralized the model constants so this research page and the live calculators use the same values. Added a downloadable CSV for offline quote planning.