Furnace Repair in Pheasant Run, CO

Altitude does not only change combustion in Pheasant Run. It changes what a cubic foot of moving air can carry away from the heat exchanger. At 5,768 feet the 15.1% derate cuts a 110,000 BTU/hr furnace to 93,390 BTU/hr of usable input, but the blower is still pushing air that holds correspondingly less mass per cubic foot, so temperature rise across the exchanger reads differently than the same equipment would read near sea level. That is why a high-limit trip in this part of Arapahoe County is an airflow question before it is a gas question.

What is temperature rise and what should it read here?

Temperature rise is the difference between supply and return air temperature with the furnace at steady state, and every furnace has a rise range printed on its rating plate, commonly a 30-degree window such as 40 to 70 Fahrenheit. The measurement is taken in the supply plenum out of line of sight of the heat exchanger so radiant heat does not corrupt it, with a clean filter installed and the burner running long enough to settle. A Pheasant Run furnace reading above its plate range is not moving enough air. Below the range, it is moving too much or firing too little.

Why does thin air push the rise upward at 5,768 feet?

Because heat transfer into an airstream depends on mass flow, not on cubic feet per minute. A blower turning at a fixed speed moves roughly the same volume in Pheasant Run as anywhere else, but that volume is 15.1% short of the mass it would carry at the pressure the equipment was rated in. Fewer pounds of air passing the same heat exchanger means each pound leaves hotter. The rise climbs, the limit switch sees temperature it was not meant to see, and the furnace shuts down mid-cycle while the thermostat still calls.

What does total external static pressure tell you?

It tells you whether the duct system is the reason the air is not moving. Most residential furnaces are rated at 0.5 inches of water column total external static, and readings well above that are common in real houses with undersized returns, crushed flex, closed dampers or a filter chosen for filtration rating rather than face area. Static is measured across the appliance, upstream of the return connection and downstream of the supply, with the filter and coil in place. A Pheasant Run furnace running high static and high rise together has a duct problem that no replacement blower motor will fix.

Which parts fail from this rather than from age?

The high limit itself, from cycling on temperature it was designed to see only as a backstop. The blower motor and its capacitor, from working against static it was never sized for. The heat exchanger, more slowly, from repeated overheating and the thermal cycling that follows every limit trip. Replacing a tripped limit switch on a Pheasant Run furnace without measuring rise and static means replacing it again next winter.

What does the 15.1% correction change about the repair?

It changes what counts as normal. A 110,000 BTU/hr nameplate gives up 16,610 BTU/hr to altitude here, so a furnace that appears to be underperforming may simply be delivering what 5,768 feet allows, while another that reads correct rise may be doing so only because it is underfired. Rise, static and manifold pressure get read together, because any one on its own can be made to tell a story that is not true.

What can be checked before the truck arrives?

Fit a clean filter of the correct size and orientation, and choose one with enough face area rather than the highest filtration rating on the shelf. Open every supply register and make sure no return grille is behind furniture. Both of those directly relieve the static pressure that pushes a Pheasant Run furnace toward its limit. If the appliance still trips after that, the restriction is inside the duct system and needs measuring rather than guessing.

Who is the permitting authority for Pheasant Run?

Pheasant Run sits in Arapahoe County, and permits for furnace replacement and gas or vent alterations run through the county building division rather than a city department. We confirm the authority having jurisdiction for the specific address before pulling a permit. MoJo Home Services has been working Arapahoe County since 2009 and is licensed and insured.

Where else nearby does MoJo work?

Around Pheasant Run we cover Centennial, Foxfield and Aurora Highlands. Call 720-807-4050 and ask for the rise and static numbers.

Other Pheasant Run-area pages

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