Only One Furnace Heats My Southern Highlands Home. What Now?

Short answer: In Southern Highlands (mostly ZIP 89141), a two-story production home often has two heating systems, and a larger custom or golf-course home may have three. When only one floor goes cold, diagnose that floor's furnace — do not replace the system that is still heating. Elevation here is about 2,390 to 2,510 feet, so gas input and orifice setup matter on every furnace visit. If you smell gas, leave the house right away. Don't use light switches, thermostats, appliance controls or anything that could spark. Once you're outside, call 911 and Southwest Gas (877-860-6020). For any other no-heat call, book online or call (702) 738-6976 to schedule.

Why Southern Highlands homes lose heat on one floor first

Southern Highlands sits in unincorporated Enterprise, Clark County — not the City of Las Vegas — even though mail reads Las Vegas. Many production neighborhoods date from the 2000s, and some still run original furnaces that sit idle through long cooling seasons and then run hard on the first cold nights.

What that layout means for heat:

• Production two-story plans usually have a downstairs furnace and an upstairs furnace. When one floor goes cold, it is usually one furnace with a problem, not both.
• Custom and golf-course lots may have three systems. A dead upstairs or casita unit is still one diagnosis, not a whole-house replacement speech.
• Townhomes and smaller plans near the parkway may have a single furnace. Those get a normal single-system check.

The area hub at Southern Highlands covers streets and AC as well. This guide stays on the winter question: one furnace down, the other still warm.

Elevation is part of the diagnosis

USGS sample points put Southern Highlands roughly 2,390 to 2,510 feet above sea level — a few hundred feet above the Harry Reid airport weather station (~2,100 feet). NFPA 54 says gas appliance input ratings apply up to 2,000 feet; above that, input is reduced by 4% per 1,000 feet, or per the manufacturer's altitude instructions.

On a Southern Highlands visit we check gas pressure and orifice setup against those instructions, not only whether the burners light. A furnace that "worked for years" can still be mis-set for this elevation after a prior parts swap. NOAA's January average low of 40.5°F is published for the airport station only; there is no separate official normal for Southern Highlands itself, but mornings on the hillside still send both furnaces into repeated ignition cycles after a long off-season.

One floor cold does not mean both furnaces are finished

Homeowners often hear that both systems should be changed together. On a Colton visit the rule is simpler:

1. Identify which furnace is calling for heat and which one is not.
2. Diagnose the failed unit: ignition, flame sensing, pressure switch, limit switch, control board, blower or venting.
3. Leave the working furnace alone unless its own safety check finds a separate problem.
4. Talk replacement only when that one unit's age, parts availability or heat-exchanger condition earns it.

Common upstairs-only winter calls:

• Burners light, then shut off after a few seconds → often a flame sensor or ignition path. See furnace flame sensor.
• Furnace never starts → furnace not turning on.
• Blower never comes on → furnace blower not working.
• Short cycles or limit trips → furnace limit switch and furnace short cycling.

For the valley service page that owns furnace work end to end, see furnace repair in Las Vegas. For broader heating (gas, heat pump and electric), see heating repair.

Gas smell and carbon monoxide are not DIY checks

If you smell gas or rotten eggs:

Leave the house right away. Don't use light switches, thermostats, appliance controls or anything that could spark. Once you're outside, call 911 and Southwest Gas (877-860-6020).

If a carbon monoxide (CO) alarm sounds, get everyone outside and call 911. Carbon monoxide has no smell of its own. See carbon monoxide and your furnace and furnace smells like gas.

If Southwest Gas left a Notice of Hazardous Conditions (Form 106.0) on the furnace, do not remove the notice or reopen the gas valve yourself. See Southwest Gas red-tag furnace.

A light dust or oil smell the first time heat runs after summer is different and often fades in a day or two. A hot plastic or electrical smell is not a gas-odor emergency, but it is a reason to leave the system off and schedule a visit. When gas odor is present, leave first — do not stay to troubleshoot.

Guard-gated sections and attic or closet furnaces

Many Southern Highlands neighborhoods are guard-gated. Add Colton Air Conditioning to the gate list for the appointment day, or tell us the entry procedure when you book. If the furnace is in a locked mechanical closet, a side-yard enclosure or an attic with a hatch that needs a ladder path cleared, say so when you schedule so the technician brings the right access plan.

Attic and closet gas furnaces need combustion air and clear working space. Do not store boxes against the furnace cabinet or block the vent path. The technician will check venting and combustion as part of a proper gas-heat visit.

Permits stay with Clark County

Because Southern Highlands is unincorporated Enterprise, a furnace replacement permit goes through Clark County Building & Fire Prevention, not the City of Las Vegas and not Henderson. Ask which mechanical permit matches the scope before anyone pulls one. Valley-wide permit map: HVAC permits in Las Vegas.

What to do next

• One floor cold, no gas smell: book a diagnostic on the failed furnace.
• Both floors cold: still a diagnosis — the cause may be shared (for example, the gas supply to the house) or two separate failures.
• Gas odor: leave the house right away. Don't use light switches, thermostats, appliance controls or anything that could spark. Once you're outside, call 911 and Southwest Gas (877-860-6020).
• CO alarm: get everyone outside and call 911.

Book online or call (702) 738-6976 to schedule.

Frequently asked questions

Only my upstairs is cold in Southern Highlands. Do I have to replace both furnaces?

No. The upstairs furnace gets its own diagnosis. The downstairs unit that is still heating stays in place unless its own safety check finds a separate problem.

Does elevation in Southern Highlands change how a gas furnace should run?

Yes. The community sits about 2,390 to 2,510 feet up. Above 2,000 feet, gas appliance input is derated per NFPA 54 or the manufacturer's altitude instructions. A visit should include gas pressure and orifice checks against those instructions.

What should I do if I smell gas when the heat tries to start?

Leave the house right away. Don't use light switches, thermostats, appliance controls or anything that could spark. Once you're outside, call 911 and Southwest Gas (877-860-6020).

I live in a guard-gated section of Southern Highlands. What do you need?

Add Colton Air Conditioning to the gate list for the appointment day, or tell us the gate procedure when you book. Mention whether the furnace is in an attic, closet or locked side enclosure.

Who issues a furnace replacement permit in Southern Highlands?

Clark County. Southern Highlands is in unincorporated Enterprise, not the City of Las Vegas.

How do I schedule heating help in Southern Highlands?

Book online or call (702) 738-6976 to schedule. Service is at the house.