The old furnace's input rating is not proof that its replacement should be the same size. Proper sizing starts with a heat-loss calculation using the home's dimensions, insulation, windows, air leakage, design temperature, and orientation. An oversized furnace can satisfy the thermostat quickly, then cycle, leaving rooms uneven and equipment stressed. An undersized system may run continuously during the coldest weather. Ask whether the proposal lists input and output capacity, efficiency, staging or modulation, and the plan for existing ducts and returns. A short conversation about basement insulation, additions, and leaky windows can materially change the result.
What to ask next
The right next step depends on the system, the urgency, and the building. Keep the model number, symptoms, age, and any previous service notes nearby when you request an estimate. A professional should explain the diagnosis or sizing basis in plain language.
When to bring in a professional
Use the callback form to describe the issue, or review HVAC services to find the closest starting point. For urgent loss of heat, see what to do in a cold snap.