Property · Improve

HVAC Load Estimate Planner

Use this to challenge tonnage-by-square-foot and identify whether the problem is load, ducts, zoning, or comfort distribution.

Estimate rough HVAC capacity pressure from square footage, climate, insulation, windows, sun exposure, duct condition, and comfort complaints before accepting a tonnage recommendation.

Start the tool How this estimate works Build decision packet Not sure where to start?

Plain English

What size AC or heat system might my home need?

This is a rough check so you do not buy size by square footage alone.

Start here: Enter home size, insulation, windows, sun, ducts, and comfort problems.

Estimate inputs

Conditioned square feetsq ftTypical ceiling heightftClimate pressureInsulation and air sealingWindow and glass loadSun exposureDuct and return-air conditionBad ducts can make the old tonnage look wrong even when the real problem is airflow.Current equipment size, if knowntonsRooms with comfort complaintsLikely project path

Result

3.8 to 5.2 tons rough capacity pressure

Midpoint pressure: 4.5 tons; Sanity-check range only, not Manual J.
Rough BTU range: 45.7k to 61.8k BTU/hr
Current size comparison: -0.5 tons vs estimate
Comfort pressure: Moderate

Flags to check

No obvious oversizing signal from current tonnage alone.
No obvious undersizing signal from current tonnage alone.
Duct condition is not the main warning from these inputs.
Envelope inputs are not strongly increasing load.
Room complaints are limited in this scenario.

Options to ask for

Manual J or equivalent load calculation

Ask for this before equipment is selected.

Square footage only is not enough for sizing.
The calculation should account for insulation, windows, orientation, air leakage, climate, occupancy, and room loads.

Pushback: Ask: what inputs changed the tonnage recommendation, and can I see the room-by-room load summary?

Duct and return-air check

Do this before buying bigger equipment.

Leaky attic ducts, crushed flex, weak returns, and high static pressure can mimic under-sizing.
A bigger unit on bad ducts can short-cycle, run noisy, and still leave rooms uncomfortable.

Pushback: Ask: what were static pressure, return sizing, duct leakage, and room airflow findings?

Right-size instead of same-size

The old size is not obviously wrong, but it still needs load support.

Current size input: 4 tons.
Rough pressure range: 3.8 to 5.2 tons.
Old equipment may have been oversized, undersized, or compensating for ducts and envelope problems.

Pushback: Ask: why is this tonnage right for the current house, not just the old unit?

Zone or mini-split the problem rooms

Only needed if room-by-room loads or ducts justify it.

Problem rooms often need targeted airflow, shading, insulation, or a ductless/ducted mini-split zone.
This can be better than oversizing the whole house for two bad rooms.

Pushback: Ask: which rooms are driving the load, and would zoning solve those rooms without oversizing the main system?

Use this page before the replacement-cost page. It decides what size/path deserves pricing.

A quote that says only "replace with same tonnage" is weak unless it explains why the old size was right.

Assumptions

Uses rough capacity pressure, not Manual J design.
A contractor should still perform a proper load calculation before equipment is selected.
Comfort complaints can be duct, return-air, solar-gain, humidity, or zoning problems rather than tonnage problems.

Decision check

Before you act on the number

The output is useful only if it survives the missing-scope, fragile-assumption, and next-step check.

Mistake check

Buying the replacement story before scope, diagnosis, ducts, warranty, or repair economics are clear.

What people forget

Cheaper service-call causes
Ducts, returns, zoning, and comfort distribution
Partial replacement or repair options
Rebate eligibility and payback limits

What makes it go bad

The quote replaces good parts
A new system still leaves comfort problems
The low bid excludes duct, electrical, permit, or warranty work

What to do next

Owners usually start with symptoms or repair-vs-replace, then compare repair, partial replacement, full replacement, and duct options.

Use the decision packet to compare scopes, missing measurements, warranty terms, and cheaper causes ruled out.

This is a sizing sanity check, not replacement pricing

The point is to challenge bad tonnage logic before a bid turns into equipment shopping. A contractor should not size by square footage alone, and they should not blindly replace the old tonnage if insulation, windows, duct leakage, additions, or room usage changed.

A bigger system can short-cycle, miss humidity removal, and still leave rooms uncomfortable.
A smaller system can be right after air sealing, insulation, window shading, or duct repair.
Hot rooms may need duct balancing, return air, shading, or a mini-split zone rather than a bigger whole-house unit.

What to ask before accepting the tonnage

Ask whether the contractor performed Manual J or equivalent load work, inspected return air, looked at duct leakage, checked static pressure, and separated load problems from distribution problems. The answer should mention the house, not just the old nameplate.