The heating bill jumps and the first suspect is always the furnace. Sometimes that is right. More often the furnace is fine and the money is leaving through the ducts, the attic, or a thermostat schedule nobody set on purpose. Here is how we sort it out when a Sacramento-area homeowner calls about the bill rather than about the heat, in the order that finds the money fastest.
First, rule out the rate
Before blaming the house, compare therms, not dollars. Your PG&E gas bill shows how many therms you used this month and the same month last year. If therms are flat and dollars are up, that is the rate, not your furnace, and nothing in this article will fix it. If therms are up, keep reading. The same applies on the SMUD side for anyone heating with a heat pump: compare kilowatt-hours, not the total.
The seven places the money goes
- Leaking ducts
- A filter that has not been changed
- A thermostat doing something you did not ask for
- An attic with too little insulation
- A furnace that is too big for the house
- An old, low-efficiency furnace
- A heat pump running on its backup heat strips
1. Leaking ducts
This is the one we find most often and the one homeowners least expect. ENERGY STAR’s figure is that a typical home loses 20 to 30 percent of the air moving through its ducts to leaks, holes and bad connections. In the 1950s and 60s ranch homes around Carmichael, Citrus Heights, Arden-Arcade and Rancho Cordova, with original ducts in the crawlspace or attic, we regularly measure worse. You are paying to heat the attic. The furnace runs longer to make up the difference and the bill shows it. Sealing and, where needed, replacing ducts is often the single best return on money spent on a heating system here, and it is not a furnace repair. See our ductwork page for what the work involves.
2. The filter
A clogged filter makes the blower work harder and the furnace run longer for the same heat, and eventually trips the high-limit switch so the furnace keeps turning on and off, which is the least efficient way a furnace can run. It is the cheapest item on this list to fix. Check it monthly in winter, especially in homes with a one-inch return grille filter, which clogs fast.
3. The thermostat
Three things to look for. A schedule that heats the house to 72 all night because a previous owner set it that way. A fan set to ON rather than AUTO, which runs the blower around the clock and costs real electricity over a winter. And on a heat pump thermostat, an “emergency heat” or “aux heat” setting left on, which we cover under item seven. Five minutes with the thermostat manual can be the whole answer.
4. Attic insulation
Heat rises, and in a house with a few inches of old insulation it rises straight out. Many of the older Sacramento homes we work in have half the attic insulation current code calls for, or less. This is not HVAC work and we do not sell it, but we point it out when we are in the attic, because it changes how long the furnace runs more than almost anything else on this list.
5. An oversized furnace
A furnace that is too big for the house heats it in short blasts, shuts off, and starts again. Every start uses more gas than steady running, and the short cycles never warm the far rooms, so people turn the thermostat up to compensate. This is common in the 1990s and 2000s tracts in Elk Grove, Natomas, Roseville and Rocklin, where builders installed one size across the subdivision. You cannot fix it with a part. You fix it by sizing the next furnace correctly, which is one of the four questions in our guide to when to replace a furnace.
6. An old, low-efficiency furnace
A furnace from the 1990s is typically rated around 80% AFUE, and a much older one may be far below that. A modern condensing furnace is 95% or higher. The difference is real, roughly fifteen to thirty percent of your heating gas depending on the ducts. But Sacramento winters are short, so efficiency alone rarely pays for a new furnace quickly. Our advice is consistent: do not replace a working furnace for the bill alone. Replace it when it is failing, and choose the efficient one then.
7. A heat pump on backup heat
If you heat with a heat pump and the electric bill spiked, the first suspect is the auxiliary heat strips. These are electric resistance elements that switch on when the heat pump cannot keep up, or when the thermostat is set to emergency heat, or when a failing outdoor unit forces them to carry the load. Resistance heat costs roughly three times what the heat pump itself costs to run. A heat pump that is quietly running on its strips every night will double a winter electric bill without anyone noticing the house is warm. If your thermostat shows “aux” or “em heat” more than briefly on a cold morning, call.
The Sacramento specifics
- Two utilities, two bills. Gas heat shows up on PG&E. Heat pump heat shows up on SMUD (or Roseville Electric). If you switched from one to the other, compare the combined total, not one bill.
- Short winter, long shoulder season. Most heating here happens in December through February, but a badly set thermostat runs the furnace on 50-degree October mornings when nobody needs it.
- The rebate side. If the answer turns out to be replacing an old furnace, SMUD currently pays $2,000 to $3,000 toward a heat pump replacing gas heat, and that changes the math. Our guide to heat pump vs furnace in Sacramento covers it.
What we do about it
A fall tune-up covers items two, five and seven: filter, cycle timing and, on a heat pump, whether the strips are engaging when they should not. If the bill is the complaint, we also check duct leakage and look at the attic while we are there, and we tell you which item is actually costing you money rather than selling a furnace. Diagnostic is a flat $69 across the Sacramento area, credited toward any work. Same-day service in Roseville, Rocklin, Sacramento, Citrus Heights, Folsom and Elk Grove; see furnace repair in Roseville and furnace repair in Sacramento.
Frequently asked questions
Why is my gas bill so high this winter?
Compare therms to last year first. If therms are flat, it is the rate. If therms are up, the usual causes are leaking ducts, a clogged filter, a thermostat schedule you did not set, thin attic insulation, or a furnace that short cycles because it is oversized.
How much heat is lost through ducts?
ENERGY STAR puts typical duct losses at 20 to 30 percent of the air moving through the system. In older Sacramento-area homes with original ducts we often measure more. Sealing them is usually the best return on money spent on a heating system here.
Will a new furnace lower my heating bill?
Moving from an 80% furnace to a 95% one cuts heating gas by roughly fifteen to thirty percent. But Sacramento winters are short, so the savings alone rarely pay for the furnace quickly. Replace it when it is failing and choose the efficient one at that point.
Why is my electric bill so high with a heat pump?
Usually the auxiliary heat strips are running more than they should, either because the thermostat is on emergency heat, the outdoor unit is failing, or the system is undersized. Resistance heat costs about three times what the heat pump does. If the thermostat shows aux or em heat for long stretches, have it checked.
Does running the fan on ON cost money?
Yes. The blower motor runs around the clock instead of only during heating cycles, and over a winter that is real electricity. Set the fan to AUTO unless you have a specific reason not to.