Arvada Furnace Repair: Venting, Draft and a 13.4% Derate

Arvada's 5,344 feet puts the NFPA 54 gas derate at 13.4%, so an 80,000 BTU/hr furnace here fires about 69,300 BTU/hr and, at 80% AFUE, delivers roughly 55,400 BTU/hr into the house. Across a city of 115,368 people, the fault we are called out to most often is not inside the furnace at all. It is the vent the furnace shares, or used to share, with the water heater.

Why does venting get the first look on an Arvada furnace?

Thin air changes both how much flue gas has to move and how buoyant it is on the way up. Combustion at 5,344 feet produces a flue volume the sea-level vent tables were not written for, which is why NFPA 54 carries a high-altitude correction. A chimney that drafted acceptably for a large, inefficient older appliance is frequently too big, too cold or too long once modern equipment is connected to it, and an oversized flue is worse than a tight one: the gas slows, falls below its dew point, and condenses inside the liner instead of leaving the building.

What goes wrong when only the furnace is replaced?

This is the orphaned water heater, and Arvada produces a lot of it. A natural-draft furnace and a natural-draft water heater were common-vented into one chimney and sized as a pair. Replace the furnace with a 95% condensing unit venting out the sidewall in PVC, and the water heater is left alone on a flue built for two appliances. At 5,344 feet, with less air mass available to carry heat up the stack, that one small burner often cannot establish draft on a cold morning. The evidence is spillage at the draft hood, rust at the flue collar, condensation on basement windows, and in the worst cases carbon monoxide in the mechanical room. Resizing and relining is the repair.

How do you test draft instead of assuming it?

With the house configured the way it really runs. Shut the doors, switch on the range hood, the clothes dryer and the bath fans, then fire the appliances and watch for spillage at the draft hood within the first minute or two. Measure draft in inches of water column at the connector against what the appliance requires, read stack temperature, and run air-free CO against the 400 ppm ANSI ceiling. A worst-case depressurization test tells you more about an Arvada basement than any amount of squinting at the chimney cap from the driveway.

What does 13.4% look like beside the cities Arvada touches?

Arvada sits on the low side of its own neighborhood. Wheat Ridge, 115 feet higher at 5,459, derates 13.8%. Golden at 5,676 derates 14.7%. Broomfield at 5,394 derates 13.6%. Arvada also covers a lot of ground and rises toward the west, so an address on the far side of the city is meaningfully higher than one near its eastern boundary. Treat 13.4% as the city reference figure rather than a guarantee for every one of the addresses that house 115,368 residents.

Which furnace faults are really venting faults?

More than homeowners expect. A furnace that locks out after three ignition attempts is often a draft problem the pressure switch caught and reported honestly. Rusted burners, a corroded inducer housing, white powdery deposits at the vent connector, and an exchanger that cracks early all trace back to flue gas condensing where it should have kept moving. Before a control board gets replaced in any Arvada furnace, the vent that furnace breathes through should already have been measured.

What can a homeowner check first?

Look where the flue leaves the furnace and where it enters the chimney. Rust flakes at a joint, or a connector that has slipped out of its fitting, is worth a call today rather than next week. On a high-efficiency unit, confirm the sidewall intake and exhaust terminations are clear of snow, ice and shrubs. Check the filter is not collapsed. If there is any exhaust smell when the furnace fires, or a CO alarm has sounded even once, shut the appliance off at the switch. Arvada's 13.4% derate does not create carbon monoxide by itself, but it removes the margin that hides sloppy venting.

Who permits furnace and vent work in Arvada?

Arvada is an incorporated city, so a furnace changeout is permitted and inspected through the city rather than through Jefferson County offices. Relining or resizing the vent as part of that work belongs to the same permit. Diagnostic visits and component repairs generally are not permitted work. MoJo Home Services is licensed, insured and EPA-certified, and has worked gas heat across the northwest metro since 2009.

Where else around Arvada do you go?

Wheat Ridge along the southern edge, Broomfield to the northeast at 5,394 feet, and Golden at the high end of this corner of the county. Heating diagnosis in any of them starts at 720-807-4050.

Same crews, neighbouring towns

Neighbouring work: furnace repair in Wheat Ridge, furnace repair in Broomfield, furnace repair in Golden.

Heating and cooling fail for different reasons in the same house — see AC repair in Arvada.

More: furnace repair · everything in Arvada.