Britain sold gas by the cubic foot until it invented the therm and billed heat instead

the problem

Gas priced per cubic foot, though heat varied, let weak gas profit while buyers fought a number measuring nothing

background

what everyone would do

Every instinct pointed at policing the gas, not its price unit: cap the price per cubic foot, or demand a declared minimum calorific value and send inspectors to enforce it, or have the state fix the quality once and for all. Each costs a standing enforcement machine, and each leaves the incentive intact — a company can still profit by shipping gas just inside the rule, so the regulator is forever chasing the next corner the seller finds.

what they saw

The fight was over the bill's unit, not over heat. Two parties haggled over cubic feet when the traded thing was heat. Change what the invoice counts and the argument vanishes; quality then prices itself.

the move

The Gas Regulation Act 1920 re-denominated the bill. Instead of charging per cubic foot, suppliers were to charge per therm — a fresh commercial unit of exactly 100,000 British thermal units, the measure of heat — and every company had to declare its gas's calorific value, so the charge tracked the heat actually delivered rather than the volume that delivered it.

why it works

Price is a unit times a quantity, and a unit sets who is to blame. Under a volume unit the seller owns the heat problem and the buyer inherits it: the supplier exploits quality because volume does not punish it, and the buyer must police a proxy it cannot cheaply measure. Re-denominating the bill in therms moves the quality information into the price quantum itself, so revenue becomes a monotone function of heat delivered — shipping weak gas now reduces the seller's own income, and no inspector is needed to make honest gas profitable. The regulator's enforcement cost collapses, the disputed proxy disappears from the contract, and the strike over frozen wartime prices is resolved because price can finally track cost.

the payoff

Pricing by therm tied revenue to heat, so weak gas stopped paying, unpoliced; the strike was defused and therms stayed the unit until 2000.

where it breaks

It only works when the re-named unit is both measurable at billing time and is what the buyer actually values. If the true value is subjective — taste, brand, convenience — no unit can be denominated in it, and insisting on one just moves the fight to a new proxy. It also fails when the measurable property is only a partial proxy: therms priced heat but not flame quality or appliance compatibility, which is why gas still needed a declared calorific value standard alongside the unit. And it is fragile if the seller can cheaply game the measurement of the new unit, or if regulatory price caps are re-imposed on the old basis, which recreates the original standstill.

what came after

The therm became the settled unit of account for British gas trading and remained so for the rest of the century; the same re-denomination logic — charge for the property actually delivered, not the tube that carries it — underlies modern energy metering and utility reform.

references

1. [1]Hansard, House of Commons — Gas Regulation Bill, Second Reading (8 June 1920)UK Parliament (Historic Hansard), 1920api.parliament.uk
2. [2]Ministry of Health. Gas Regulation Act, 1920The Analyst (Royal Society of Chemistry), 1923doi.org
3. [3]Gas Act 1986, Section 12 — Standard method of chargelegislation.gov.uk (UK Government), 1986legislation.gov.uk

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