HVAC installation is faster than most homeowners expect — a furnace replacement can be done in four to six hours. That speed means the window for asking questions during the job is short, and the questions that matter most are specific. Here’s what to ask and when.
“The commissioning at the end of an HVAC installation is the step that separates a professional job from an adequate one. Running the system, measuring airflow, checking gas pressure, testing for CO — that’s where you find out if the installation was done right. Ask your contractor to walk you through the commissioning results before they pack up. If they resist, that tells you something.”
— Ravi Menon, licensed HVAC technician and gas fitter with 20 years of experience in residential heating, cooling, and heat pump installation in the local area
Table of Contents
Before Work Starts
Can you walk me through the installation plan?
Ask the lead technician to give you a brief overview: where the new equipment will be positioned, what connections will be made, which systems will be shut down and for how long, and approximately how long the installation will take. This orients you and gives you a reference point if something changes.
How long will I be without heat or cooling?
For furnace replacements in winter, ask specifically how long the system will be offline. In very cold weather, you may want to make arrangements for vulnerable family members or pets. Most furnace replacements restore heat within four to six hours.
During Equipment Installation
Can I see the equipment model number before installation?
Before the new equipment is connected and running, ask to see the model number on the unit. Confirm it matches what was quoted. It should be easy to verify — the rating plate is always on the unit itself.
What a good answer looks like: A visible model number that matches the quote, confirmed before installation proceeds.
Is the old equipment being fully removed?
For replacements, confirm that the old furnace, air handler, or condenser is being fully removed — not left in place alongside the new unit. Old equipment left in the mechanical room creates confusion, takes up space, and may be improperly decommissioned.
How is the venting being handled?
High-efficiency furnaces (90%+ AFUE) vent combustion gases through PVC pipe, not through the chimney flue used by older 80% units. If you’re upgrading from a lower-efficiency to a high-efficiency furnace, ask how the venting change is being handled — is the chimney being capped, is the PVC being run through the existing penetration or a new one, and where does it terminate?
What a good answer looks like: A clear explanation of the venting plan and confirmation that the old chimney flue is being properly capped or decommissioned.
During Commissioning
Commissioning is the final step of a professional HVAC installation — running the system and verifying it’s operating correctly. Ask to be present for this step.
Can I be present for the commissioning?
Commissioning is when the system is started for the first time under the technician’s supervision. Being present gives you the opportunity to see the system running, ask questions in real time, and confirm that the commissioning steps are actually being performed.
What is the measured supply air temperature?
For a new furnace, ask what the supply air temperature is — the temperature of the air coming out of the registers. A properly operating furnace should produce supply air approximately 30–50°C warmer than the return air temperature. A very low rise may indicate an airflow problem; a very high rise may indicate an undersized unit or a duct restriction.
What is the static pressure reading?
Static pressure measures the resistance in the duct system. Too much static pressure means the air handler is working harder than it should, reducing efficiency and lifespan. Ask the technician what the measured static pressure is and whether it’s within the manufacturer’s specifications.
Has a carbon monoxide test been performed?
A CO test after installation of any gas appliance is a basic safety step. Ask specifically whether it’s been done and what the result was. The answer should be zero detectable CO in the living space.
Has a combustion analysis been performed?
A combustion analysis verifies that the furnace is burning fuel at the correct air-fuel ratio — confirming efficiency and safety. Ask whether this was done and what the results showed.
Is everything on the startup checklist complete?
Ask the technician to go through their startup checklist with you. A professional installation company will have a written commissioning checklist — this is a reasonable thing to ask to see.
Before the Technician Leaves
Can you show me how the system operates and how to use the thermostat?
Before the technician leaves, ask for a walkthrough of how the system works, how to use the thermostat (particularly if it’s a new smart or programmable model), and what the normal operating sounds and behaviors are. This baseline helps you identify anything unusual later.
What should I watch for in the first few weeks?
Ask specifically: what behaviors would indicate a problem in the first days or weeks of operation? Short cycling, unusual noises, failure to reach set temperature, CO detector activation — knowing what to watch for helps you catch issues early.
When does the warranty registration need to be completed?
Many manufacturer warranties require registration within 30–90 days. Ask who is responsible for registration and what the deadline is.
Related Questions
- Questions to Ask an HVAC Contractor Before You Hire One
- Questions to Ask an HVAC Contractor About Warranties
- Questions to Ask an HVAC Contractor About Maintenance
- What to Do If an HVAC Contractor Does Bad Work
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