Greater St. Louis heats mostly on Spire gas at the core, but the metro's full heating ledger runs wider and more expensive than the gas map suggests. Propane trucks serve the exurban edges past the last mains, out through the far reaches of St. Charles and Jefferson counties. Oil furnaces survive in older farmhouses on the fringe. Electric baseboard hides in South City four-family conversions and University City flats, buildings cut into apartments decades ago, and in additions across the brick neighborhoods. Aging heat pumps in the postwar rings quietly burn resistance-strip money through every cold snap. This guide runs the conversion arithmetic for each case, with a two-season climate improving the answer in a way most heating guides forget to count.
The Ledger in One Table
| Existing heat | Case for a heat pump | Strength |
|---|---|---|
| Heating oil | Truck-priced fuel loses to metered kilowatt hours moved at multiple efficiency | Strong |
| Propane | Usually the metro edge's most expensive delivered heat | Strongest |
| Electric resistance | Same meter, a half to a third the consumption for the same warmth | Strongest |
| Aging heat pump | Modern variable-speed machine holds capacity through the snaps, retires the strips | Strong |
| Natural gas | Closest race; the equipment calendar and the AC usually settle it | Honest maybe |
Delivered Fuel: The Truck Stops Coming
A household past the gas mains buys heat in large lumps, a tank fill at a time, at prices that swing with a market it cannot negotiate with. A heat pump replaces those gallons with kilowatt hours that move two to three units of heat per unit of electricity, billed monthly at Ameren rates that move slowly. The saving shows up in four figures for most conversions, and its shape is distinctive: the delivery line disappears entirely, the winter electric bill rises, and the year-total falls. St. Louis sweetens the deal from the other season, because the same machine replaces the aging air conditioner these households were going to buy anyway. These are the fastest-payback whole-home projects in the region, priced in our installation cost guide, and the FastTrack rebate trims the front end.
Electric Resistance: Arithmetic on a Single Bill
Resistance heat, baseboard, ceiling cable, wall units, converts one unit of electricity into one unit of warmth, full price, every hour. A heat pump on the same meter at the same rate moves two to three units of warmth per unit purchased. No fuel forecast, no rate speculation, no assumptions: the same bill simply shrinks toward a half or a third for the heating share. In the metro's rental and conversion stock, South City four-families and the University City flats near the Loop above all, this is the most common expensive-heat configuration and the strongest case in this guide. And because most of that stock cooled itself with window units, the conversion adds real air conditioning to the same invoice, a comfort upgrade the resistance math gets for free in a metro whose Augusts demand it.
The Aging Heat Pump, the Quiet Money Leak
The postwar rings, Kirkwood, Webster Groves, the Creve Coeur corridor, out through Chesterfield MO, hold earlier-generation heat pumps that were honest machines in their day and are strip-heaters in this one. Below the temperatures where their compressors fade, they hand the load to electric resistance backup at full resistance rates, precisely when the cold snap makes the load largest. The bill signature is unmistakable: tolerable shoulder months, ugly January statements. A modern variable-speed replacement, specified against published capacity tables per our cold-weather guide, holds output through the metro's single-digit nights, retires the strip habit, and then spends the summer out-cooling the machine it replaced.
The Honest Spire Paragraph
A household with a functioning furnace on Spire's grid faces the closest race in the region, and deserves it stated coldly. Gas is cheap heat in Missouri, and displacing a mid-life furnace rarely pays on fuel savings alone. The conversion cases that clear anyway are calendar cases, and in St. Louis the calendar has two hands: the furnace at end of life, where the replacement dollar was being spent regardless, and the air conditioner also due, which in this climate is the more common trigger and the stronger argument, since one machine replaces both. Dual fuel, a heat pump carrying the season with the furnace held for the deepest snaps, is a legitimate configuration a good contractor prices without being asked. What no honest bidder does is promise a gas household dramatic savings; a bid that does has failed the first test in our contractor guide.
Reading the First Year Correctly
Judge the conversion by shape, not by a single statement. The delivered-fuel convert sees a larger winter electric bill and a smaller year, because the truck line vanished. The resistance convert sees the same warmth cheaper immediately, plus air conditioning. The heat pump replacer sees the cold snaps flatten and the summer improve. The discipline that makes all three legible is one ledger: last year's total heating and cooling spend, every source, next to this year's, read whole year against whole year each spring. January in isolation is the wrong number, and in a metro that spends real money on August, it is barely half the story.
Renters, Landlords, and the Split Incentive
The metro's most expensive heat disproportionately warms people who cannot replace the equipment: baseboard in South City four-families, tired window units above the Loop, resistance additions across the brick neighborhoods. The tenant pays the bill; the owner owns the fix; and the arithmetic in this guide reads identically for both, with only the beneficiary line changing. The owner's case needs no subsidy: a rebated purchase through Ameren's FastTrack pathway, per our rebates guide, a large operating improvement, real air conditioning in stock that mostly never had it, and a bill a tenant can pay. A tenant's cheapest and most effective move is forwarding this page to whoever holds the deed, with one sentence attached: the heating system is costing us both money.
One Rule Before Any Conversion
Every case above assumes the machine was specified for St. Louis's actual coldest nights: published capacity at the design condition beside a room-by-room load calculation, backup sized as a safety net rather than a crutch, and the summer load counted with the same seriousness. The arithmetic in this guide is fuel arithmetic; the specification discipline is what keeps it true through the first cold snap and the first heat wave alike.
The Short Version
Propane and oil lose to the heat pump on truck-versus-meter arithmetic. Resistance loses on a single bill's multiplication and throws in air conditioning as the consolation prize. Aging heat pumps lose on their strip habit. Functioning Spire furnaces make it a fair fight that the equipment calendar, usually the air conditioner's, settles. The math carries every case from Soulard to Chesterfield MO, and the rebate arrives on the invoice.
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