Questions to ask before you hire an HVAC contractor in Denver
In Denver, an HVAC system has to handle cold winter nights, sunny days with big temperature swings, and dry summer heat, all at about a mile above sea level, where gas furnaces and water heaters may need altitude adjustments to burn safely. Many older bungalows and Denver Squares still cool with evaporative coolers, some heat with boilers, and spring and summer hail can batter outdoor units. Colorado has no statewide HVAC license, so in the city the question is which City and County of Denver HVAC contractor license your job runs under, and whether the permit is pulled in the contractor’s name. Use these questions to compare Denver-area HVAC contractors on verified credentials, sizing and altitude setup, safe venting, and a written scope, not just who can come out today.
Questions to ask
1. Who is the licensed contractor on my job: which City and County of Denver HVAC contractor license do you hold (or the license my suburb requires), and can I see the number?
Why it matters: Colorado is one of the states that does not license HVAC contractors or technicians at the state level (DRCOG), so licensing is handled by each city or county. Inside the City and County of Denver, mechanical work runs under a Denver contractor license matched to the job: for a house or duplex that is usually the Heating Ventilating Air Conditioning Contractor (Residential Only) license, which covers furnaces, ductwork, evaporative coolers, gas piping, venting, and air conditioning up to 5 tons, or a Heating and Ventilating Class B license plus a Refrigeration Contractor Class B license for the cooling side; hot-water (hydronic) boilers fall under the Hot Water or Steam and Hot Water licenses, and steam boilers need the Steam and Hot Water license (Denver license classifications). Before Denver issues a contractor license, the business must hold or employ a Denver supervisor certificate holder for that trade (Denver supervisor certificates). Any new circuit or disconnect for a heat pump or condenser is electrical work, which needs a Colorado-licensed electrical contractor that is also licensed in Denver (Denver contractor license requirements). Aurora, Lakewood, Arvada, Centennial, Boulder, and other Front Range cities and counties run their own licensing, and a Denver license does not automatically cover them, so check your own jurisdiction. Verify the license on the Denver contractor license search (or your suburb’s list), make sure the license type fits your equipment, and ask for a current liability insurance certificate.
2. Which technicians on my job hold EPA Section 608 certification, and are they trained on the newer A2L refrigerants?
Why it matters: Anyone who installs, services, or repairs equipment containing refrigerant must hold EPA Section 608 certification or work under the direct supervision of someone who does (EPA Section 608). Many newer air conditioners and heat pumps sold since the federal refrigerant transition use A2L refrigerants (such as R-454B or R-32), which have their own handling and installation requirements. Ask who on the crew is certified, whether they have installed the refrigerant your proposed system uses, and how they will recover refrigerant from the unit they remove. If your central air still runs on R-22, ask plainly whether a repair still makes sense or whether replacement is the honest answer.
3. Will you run a Manual J load calculation for my house at Denver’s altitude and climate, instead of matching the old unit’s size?
Why it matters: Denver sits about a mile above sea level, with cold winter nights, sunny days that can swing widely in temperature, and hot but very dry summer afternoons. Heating is usually the bigger load, but west-facing rooms and upper floors can overheat in July. A Manual J (or equivalent) load calculation should account for local design temperatures, elevation, insulation, windows, air leakage, and where the ducts run, and you should get the results in writing. Oversizing is a common problem in older Denver bungalows, Denver Squares, and mid-century ranches, especially when each replacement was matched to the last unit: oversized equipment short-cycles, wears out sooner, and leaves rooms uneven. Ask how the proposed system will keep up during a subzero cold snap and a 95-degree afternoon, whether thinner air at altitude affects the equipment they chose, and whether insulation or air sealing would let you buy smaller equipment.
4. How will you set up the furnace, boiler, or water heater for high altitude, and will you combustion-test it and check venting and carbon monoxide safety?
Why it matters: Gas appliances burn differently in thin air. Gas furnaces generally must be derated for altitude, typically 4% per 1,000 feet above 2,000 feet. Manufacturers do this with smaller burner orifices and, on some models, a high-altitude kit such as a different pressure switch. Gas pressure should be checked against the nameplate, not turned down to derate (Johnson Controls high-altitude kit manual; Trane high-altitude pressure switch kit guide). Ask whether the equipment they quote is approved for your elevation, what adjustments they will make, and whether they will measure combustion and carbon monoxide with an analyzer and leave you the readings rather than just checking that the burner lights. Ask where any side-wall vents on a high-efficiency furnace will exit, how high above expected snow and drifts, and how the condensate line will drain without freezing. If an old furnace shared a masonry chimney with a gas water heater, ask whether the water heater will be left alone in an oversized chimney and whether a liner or venting change is needed. Colorado law requires an operational carbon monoxide alarm within 15 feet of the entrance to each room used for sleeping when a single-family home with fuel-fired appliances or an attached garage has a fuel-fired appliance replaced, or other work done, under a building permit, and when a home with a fuel-fired heater or appliance, a fireplace, or an attached garage is sold (C.R.S. 38-45-102); ask the contractor to confirm your alarms are in place.
5. Would a high-efficiency gas furnace, a cold-climate heat pump, or a dual-fuel system fit my home, and how will it heat on the coldest nights?
Why it matters: Most Denver-area homes heat with natural gas, but cold-climate heat pumps and dual-fuel systems (a heat pump paired with a gas furnace as backup) are increasingly offered, and several current incentives favor cold-climate heat pumps (see question 9). Press on cold-weather performance. Ask for the manufacturer’s rated heating capacity at low outdoor temperatures such as 5°F, what backup heat is included (gas furnace or electric resistance strips), at what outdoor temperature the system switches to backup, and what electric strips would mean for your panel and your Xcel Energy bill. If you keep gas, ask how the furnace’s efficiency (AFUE) and blower type affect comfort and operating cost. A good contractor compares options for your house and explains the trade-offs; be wary of anyone who pushes one answer without looking at it.
6. Is an evaporative (swamp) cooler, central air, or a heat pump the better way to cool my home, and where will the outdoor equipment go?
Why it matters: Denver’s dry air is why many older homes still cool with evaporative coolers, which use far less electricity than air conditioning but add moisture, work less well on muggy days, and need regular pad changes, water-line care, and draining and covering before the first freeze. Ask the contractor to compare an evaporative cooler, central air, and a heat pump for your house honestly, including operating cost, maintenance, and how much each will actually cool upstairs rooms. If you are replacing a roof-mounted cooler, ask how the roof opening and duct will be sealed and who handles any roof work. For condensers and heat pumps, ask where the outdoor unit will sit relative to snow sliding off the roof, drifting, and summer hail, which can damage coil fins. If they suggest a hail guard or cover, ask whether the manufacturer allows it, since anything that restricts airflow can hurt performance or warranty coverage.
7. What will you check on ducts, dry air, and old boilers, and how do you handle old materials that may contain asbestos?
Why it matters: Ask whether they will inspect and pressure-test the ducts and what sealing, balancing, or return-air fixes they recommend for rooms that are always too hot or cold, especially second floors and finished basements. Winter air in Denver is very dry, so ask whether a humidifier makes sense, what type, and how it would be maintained. Some older Denver homes heat with hot-water or steam boilers and radiators and have no ducts; if that is your house, ask whether the contractor regularly works on boilers, whether a replacement is sized from a heat-loss calculation rather than the old boiler’s rating, and what ductless mini-split options would add cooling. Older basements and boiler rooms often have pipe insulation, boiler insulation, duct wrap, or flexible duct connectors that may contain asbestos. Colorado’s health department says the only way to know is lab testing, and many renovation projects, including replacing mechanical ventilation systems or pipes, must be inspected by a Colorado-certified asbestos building inspector before work starts once suspect materials exceed state trigger levels (CDPHE asbestos). Ask how they handle suspect materials before anyone disturbs them.
8. Does my job need a Denver or suburban permit, who pulls it, and is the inspection included?
Why it matters: Denver says most construction or repair projects on single-family homes and duplexes require a permit, and its short list of exempt work does not include HVAC equipment (Denver homeowner permits). For houses and duplexes, Denver issues mechanical and boiler/AC quick permits, which do not need plan review and are inspected in the field, for work such as forced-air heating systems, residential air conditioning, evaporative coolers, ductwork, gas piping, and water heaters, and separate electrical quick permits for new circuits and disconnects (Denver quick permits). Work on an individual landmark or in a historic district that involves exterior equipment needs Landmark Preservation review first, and condos and apartment buildings follow Denver’s separate commercial and multifamily equipment replacement rules. Suburbs such as Aurora, Lakewood, Arvada, Centennial, and Boulder follow their own rules. Ask the contractor to pull the permit in their own company’s name (Denver specifically warns homeowners to avoid contractors who want permits pulled in the owner’s name), whether permit fees are in the quote, and who schedules the inspection. Hold your final payment until the inspection passes.
9. Which Xcel Energy, Power Ahead Colorado, or state heat pump programs might apply, and will you handle the paperwork?
Why it matters: Most of Denver gets electricity and natural gas from Xcel Energy, which runs residential heat pump rebates; its Xcel heat pump page currently says invoices and installations must be completed by Dec. 31, 2026, and that the contractor typically completes the application. The Denver Regional Council of Governments’ Power Ahead Colorado program offers rebates on qualifying cold-climate air-source heat pumps in participating Denver-area communities, but only through an approved contractor who submits the project before work begins. Colorado’s heat pump tax credit is claimed by contractors registered with the Colorado Energy Office, who must pass part of it to you as a discount shown as a separate line on the invoice (Colorado Department of Revenue). Some outlying suburbs get electricity from a co-op or municipal utility with different programs. Ask which programs the contractor participates in, which equipment ratings each depends on, who submits what and by when, and get any promised amount in writing as an estimate, not a guarantee. The federal Energy Efficient Home Improvement Credit (25C) ended for equipment placed in service after Dec. 31, 2025 (IRS), so a system installed in 2026 does not qualify for it; be wary of any quote that still counts a federal tax credit. Verify current rules directly with each program before you sign.
10. What does the written estimate include: model numbers, venting, duct or piping work, electrical work, disposal, and a labor warranty?
Why it matters: A good quote lists the exact indoor and outdoor model numbers, efficiency ratings, thermostat, line set, pad or wall bracket, venting and any chimney liner, high-altitude conversion if needed, condensate drain or pump, duct or boiler piping changes, humidifier if included, electrical work for a heat pump or condenser, permit fees, and disposal of the old equipment or evaporative cooler. Ask how they handle surprises like a corroded flue, asbestos-suspect material, a cracked heat exchanger, or tight crawlspace or attic access, and require a stop-and-call change-order process before extra work. Get the manufacturer warranty and the contractor’s labor warranty in writing separately, and confirm who registers the equipment so the manufacturer warranty applies.
11. How do you handle no-heat calls during a cold snap and no-cooling calls in a heat wave, and can you give me recent Denver-area references?
Why it matters: Losing heat during a Front Range arctic blast can freeze pipes along exterior walls and in crawlspaces within hours, and older adults, young children, and pets are at risk; summer heat waves can be dangerous too. Every HVAC company in the region gets slammed at once. Ask what response time looks like for existing customers during those surges, what after-hours and weekend rates apply, whether a maintenance plan actually moves you up the list, and what a fall tune-up includes before heating season. Then ask for two or three recent local references for similar homes, such as a furnace and AC in a Park Hill bungalow, a heat pump in a Lakewood ranch, or a boiler in an older Denver Square. References tell you about punctuality, cleanup, and whether the system was set up right the first time, which star ratings alone often miss.
Red flags
Quotes a replacement size over the phone or by matching the old furnace, boiler, or AC, with no load or heat-loss calculation.
Cannot tell you which City and County of Denver (or suburban) contractor license the job is under, or which licensed electrical contractor will do the wiring.
Asks you to pull the permit in your own name, or offers a lower price to skip a permit.
Says nothing about high-altitude setup, plans to derate by turning down gas pressure instead of following the manufacturer’s high-altitude instructions, or will not combustion-test a new gas furnace, boiler, or water heater.
Vague about which refrigerant the new system uses or who on the crew is EPA 608 certified.
Pitches a heat pump without explaining cold-weather capacity, backup heat, and what electric strips need from your panel.
Dismisses an evaporative cooler or pushes one without comparing cost, maintenance, and comfort for your house.
Ignores side-wall vent placement for snow, condensate freezing, an orphaned water heater in the chimney, or carbon monoxide alarms.
Disturbs old pipe insulation, boiler insulation, or duct wrap without talking about asbestos testing.
No model numbers, no venting, duct, piping, or electrical scope, and no written labor warranty on the estimate.
Promises a specific rebate or tax credit as guaranteed, still counts the expired federal 25C credit, or starts work before a required rebate preapproval.
Next-step checklist
Ask each contractor which license the job is under and look it up on the Denver contractor license search or your suburb’s contractor list.
Get at least two written quotes for the same scope, with model numbers, efficiency ratings, and venting, duct or piping, and electrical work listed.
Ask each contractor to share their load or heat-loss calculation and explain how the system handles a subzero cold snap and a hot, dry afternoon.
Ask what high-altitude adjustments the gas equipment needs and request the combustion and carbon monoxide readings after startup.
Confirm your AHJ (City and County of Denver or a suburban city or county), that the contractor pulls the permit in their name, and who schedules the inspection.
Make sure you have working carbon monoxide alarms near every sleeping room.
Ask where the outdoor unit and any side-wall vents will go relative to roof snow, drifts, and hail, and how condensate will drain in winter.
Ask about asbestos testing before anyone disturbs old pipe or boiler insulation, duct wrap, or flue materials.
Check current incentives directly with Xcel Energy, Power Ahead Colorado, and the Colorado Energy Office before you sign, and confirm any preapproval happens before work starts.
Agree in writing on equipment placement, filter location, warranty terms, payment schedule, and a stop-and-call change-order process; hold final payment until inspection passes.
Keep the permit record, warranty registrations, and final invoice for resale and future service.