Sudden High Energy Bills in Millwood, WA

A furnace that's suddenly less efficient has a reason. Here are the most common root causes - explained the way a neighbor with 20 years of HVAC experience would explain them.

Dirty or Clogged Air Filter

This is the most common cause, and it's deceptively simple. A clogged filter restricts airflow through the system. When airflow drops, the furnace has to run longer to move the same amount of heat through your home. Longer run times mean higher fuel and electricity consumption.

In Millwood's older housing stock - especially homes built during the building booms of the late 1990s and early 2000s near the Millwood Historic District - builder-grade HVAC systems are now 15 to 20+ years old. Many of these units were designed with minimal filter maintenance in mind. They're not forgiving when filters go unchanged.

Duct Leaks

Your ductwork is the delivery system for your heat. If it's leaking - and in older homes, it often is - conditioned air escapes into unconditioned spaces like attics, crawlspaces, and wall cavities. Your furnace keeps running because the thermostat never sees the target temperature.

Duct leaks are invisible from the outside. You won't see them. But your energy bill will.

Failing Blower Motor or Capacitor

The blower motor moves heated air through your ducts. When the motor starts to fail - or when the capacitor that helps it start weakens - the motor draws more electrical current to do the same job. That shows up directly on your electric bill.

A motor running at reduced efficiency also creates heat buildup inside the unit, which can trigger safety shutoffs and cause the furnace to short-cycle (turn on and off repeatedly). Short-cycling burns more fuel per hour of actual heating than a furnace running normal cycles.

Dirty Burners or Heat Exchanger

Over time, burners accumulate dust, rust, and combustion byproducts. Dirty burners produce an uneven, inefficient flame. The furnace extracts less heat from each unit of gas it burns - and compensates by running longer.

A cracked or corroded heat exchanger compounds this. The heat exchanger is the metal barrier between combustion gases and the air circulating through your home. When it's compromised, combustion efficiency drops and - critically - CO can enter your living space.

Thermostat Calibration or Wiring Issues

A thermostat that reads the temperature incorrectly will call for heat more often than needed. This is easy to overlook because the thermostat looks like it's working. But if it's reading 2–3 degrees low, your furnace runs 10–15% more than it should.

Wiring faults can cause similar behavior - the system cycles on when it shouldn't, or fails to shut off cleanly.

Age and Wear (Builder-Grade Units)

Here's the dirty secret about builder-grade furnaces: they're designed to meet code at installation, not to last 25 years. Many homes near the Argonne Road corridor and the Inland Empire Paper Company Mill area were built during the same construction windows, which means a lot of original HVAC equipment is hitting the end of its expected service life right now.

A furnace that's 15–20 years old and losing efficiency isn't necessarily broken - but it is working harder. Annual efficiency ratings (AFUE) degrade with age and wear. A unit that was 80% efficient at installation may be running at 65–70% today.

Before you call, run through these checks. They're safe, they take five minutes, and they might save you a service call.

1. Check your air filter. Pull it out and hold it up to a light source. If you can't see light through it, it's overdue for replacement. Replace it with the same size and MERV rating. 2. Check your thermostat settings. Make sure it's set to "Heat" and "Auto" (not "Fan On"). A fan running continuously moves unconditioned air and inflates your bill. 3. Check your vents and registers. Walk through your home and confirm that supply and return vents are open and unobstructed. Furniture, rugs, and drapes blocking vents force the system to work harder. 4. Check for obvious duct disconnections. If you have accessible ductwork in a basement or crawlspace, look for sections that have pulled apart or are visibly separated at joints. 5. Listen to your furnace. Note any unusual sounds - grinding, squealing, or repeated short on/off cycles. These are useful details for your technician.

Stop here if you smell gas or rotten eggs. Leave the home immediately, avoid switches and open flames, and contact your gas utility.