Keeping Gas for One Appliance

Why this matters

Plenty of customers who convert their heating and hot water want to keep gas for one thing: the fireplace they sit in front of all winter, the range they have cooked on for twenty years, sometimes the dryer. That is a legitimate choice and it is theirs to make. The trouble is that most of them make it without knowing what it costs, and the cost is not the gas they burn. It is the fixed monthly charge the utility bills whether they burn any gas or not, which is now paying for one small appliance. Then, months later, the first gas bill after the conversion arrives and looks wrong to them, and the call comes to you.

This card covers the honest version of that conversation: what the fixed charge does to the per-unit cost of the gas that remains, what the remaining appliance still needs for venting and CO safety, and how to lay out the choice without pushing it.

The fixed charge, explained

A residential gas bill usually has two kinds of charges. Volumetric charges scale with use: supply and delivery per therm (or per hundred cubic feet, ccf, which is close to a therm in energy). Fixed charges do not: a monthly customer charge, sometimes called a service charge or basic charge, set in the utility's tariff and approved by the state utility commission. Some tariffs add riders that are fixed per month as well. The fixed charge pays for the meter, the service line, meter reading and billing, and the utility charges it for as long as the meter is active.

While the furnace and water heater were on gas, the fixed charge was a modest share of a large bill. With one small appliance left, the volumetric part shrinks to a fraction and the fixed part stays exactly where it was. Two things follow:

• The bill does not fall as far as the gas use does. A customer who cut gas use by 90 percent will not see a 90 percent smaller bill.
• The effective price of each therm still burned goes up, because the fixed charge is now spread across far fewer therms.

Neither of those is a rate increase. It is the same tariff applied to a different house.

Worked example: the fireplace and the range

Work it in the customer's own units, without currency, by expressing the monthly fixed charge as the number of therms it would buy at the customer's volumetric rate. Read both off their bill. In this illustrative case, the fixed charge each month equals the volumetric cost of 12 therms, so the fixed charge for a year is the cost of 144 therms.

Before the conversion. The house used 760 therms a year for furnace, water heater, range and fireplace. The year's bill equals the cost of 760 + 144 = 904 therms. The fixed charge is 144 of 904, about 16 percent of the gas bill. The effective cost per therm burned is 904 / 760, about 1.19 times the volumetric rate.

After, keeping the fireplace. A direct-vent gas fireplace used most winter evenings, say 70 therms a year (estimate it from its input rating and the hours the customer actually runs it). The year's bill equals the cost of 70 + 144 = 214 therms. The fixed charge is now 144 of 214, about 67 percent of the gas bill. The effective cost per therm burned is 214 / 70, about 3.06 times the volumetric rate, which is about 2.6 times what each therm effectively cost before (3.06 against 1.19).

After, keeping only the range. A gas range in regular use, say 25 therms a year. The bill equals the cost of 25 + 144 = 169 therms; the fixed charge is 144 of 169, about 85 percent; each therm cooked with effectively costs 169 / 25, about 6.8 times the volumetric rate, about 5.7 times what it cost before.

What the customer should take from it. Keeping the fireplace means paying, each year, about twice as much for the meter as for the gas the fireplace burns (144 against 70). Keeping only the range means paying almost six times as much for the meter as for the cooking gas (144 against 25). Both may still be worth it to them. They should decide knowing it.

The numbers are illustrative; the method is the deliverable. Fixed charges vary widely between utilities and states, from a small share of a typical bill to a large one, and the customer's tariff is the only source.

The conversation, without the sales pitch

CUSTOMER: We want to keep the gas for the fireplace.
TECH: That works fine. One thing to know first.
      Your gas bill has a monthly charge just for
      having the meter. It doesn't change with use.
CUSTOMER: How much of the bill is that?
TECH: Today, about a sixth. After the furnace and
      water heater go, it'll be about two-thirds,
      because the fireplace uses so little gas.
CUSTOMER: So the bill goes up?
TECH: The bill goes down a lot. But per unit of
      gas, the fireplace costs about two and a half
      times what that gas costs you now.
CUSTOMER: What would it take to drop gas entirely?
TECH: An electric insert, or no fireplace. I can
      price that, and you can decide either way.

What that exchange does right: it states the fact before the customer asks, gives one ratio rather than a column of figures, separates "the bill goes down" from "each therm costs more" because those two are easy to hear as a contradiction, and offers the alternative without arguing for it.

The remaining appliance still has to vent

Keeping one appliance means keeping its safety requirements, and the conversion can change them.

A gas range is not vented to a flue; its combustion products go into the kitchen, and the hood is what removes them. Recommend running the hood whenever a burner or the oven is on. A conversion that tightens the house leaves less leakage to dilute them.

A direct-vent gas fireplace draws combustion air from outdoors and exhausts outdoors through a sealed vent. It is the least affected by house depressurization, but its vent termination and glass gasket still get the manufacturer's annual service.

A natural-draft appliance (a B-vent fireplace, or a natural-draft water heater kept on gas) depends on draft, and the conversion's new hood, tighter envelope and missing furnace can all weaken it. See related: Combustion Safety After a Partial Conversion, which owns the depressurization test, and What Removing a Gas Appliance Does to the Ones Left, which owns the flue consequence when a shared vent loses its furnace.

Decorative gas logs in a masonry fireplace require the damper to stay permanently open, typically with a damper clamp, under the fuel gas code (IFGC or NFPA 54) as adopted for decorative appliances in vented fireplaces. A customer who closes the damper to stop heat loss creates a CO hazard.

Vent-free gas logs and room heaters exhaust into the room by design. Some states and localities restrict or prohibit them, and they deserve a frank word when a customer says the logs are why they are keeping gas.

A gas dryer keeps its exhaust duct, which stays a lint fire and backdraft point; it is also an exhaust device that depressurizes the house.

CO alarms stay

As long as a fuel-burning appliance remains, the CO alarm requirement remains: the IRC, as adopted, requires alarms in dwellings with a fuel-fired appliance or an attached garage with an opening into the dwelling (R315 in the 2021 edition), and many states add their own requirements on top. A one-appliance house is easy to think of as an electric house. It is not, for this purpose. See related: Smoke and CO Alarm Requirements Your Permit Triggers.

What changes the answer

Resilience. A gas range's burners can usually be lit with a match during a power outage (most ovens cannot, because their ignition and safety valves need power), and a fireplace with a standing pilot or battery ignition can heat a room with no electricity, provided it is rated to run without its blower. For a customer in an area with long outages, that is a real benefit and worth naming. Check the appliance manual rather than assuming it runs without power.

Leaving gas entirely. Stopping the fixed charge means closing the account and usually having the meter removed. Some utilities charge for removal or require a service line abandonment, and some leave the meter locked. Seasonal shutoff is not the same: many tariffs keep billing the fixed charge through the off months or charge a reconnection fee. See related: How to Close Out Gas Service With the Utility.

A dryer as the one appliance. A gas dryer uses more gas than a range, so the fixed charge share is smaller, and swapping it is often easier than swapping a fireplace. See related: How to Install a Heat Pump Dryer and Close the Old Vent.

Fixed charges that change. Some states are reviewing how gas utilities recover fixed costs as customers leave, and fixed charges can rise. Do not forecast; tell the customer the charge is set in the tariff and can change.

How to verify you gave them the right picture

Read the fixed and volumetric charges off the customer's own bill, not a statewide average. Estimate the remaining appliance's annual use from its input rating and the customer's real habits. Express the fixed charge as therms per year at their volumetric rate, then compute the before and after shares the way the example does. If you can tell the customer, in one sentence with one ratio, what keeping the appliance costs per unit of gas and what dropping it would take, you have given them a decision instead of a surprise.

References

• Your gas utility's tariff on file with the state utility commission (customer and service charges)
• International Residential Code Section R315, 2021 edition as adopted; International Fuel Gas Code or NFPA 54 as adopted, for decorative appliances in vented fireplaces
• See related: Combustion Safety After a Partial Conversion; How to Close Out Gas Service With the Utility; Smoke and CO Alarm Requirements Your Permit Triggers