How to run a Korean gas boiler in winter and read the city gas bill

Most foreign residents in a one-room, villa or officetel heat their home with their own gas boiler, a wall-mounted box that warms water and pumps it through pipes under the floor.
That setup decides three things: you pay a monthly city gas bill, the controller on your wall runs the whole system, and the boiler's freeze protection only works if you leave it powered.
This guide covers each of those in order, and then the safety steps that matter more than the bill.

First, check which kind of heating you have

It takes about 30 seconds, and it tells you where the cost will appear.

With district or central heating, you only control room thermostats or valves.
Most of the bill section below won't apply to you, and the boiler buttons work differently.
For district heating, Korea District Heating Corporation (KDHC) has advised using away mode for trips of three days or more and leaving room thermostats on all winter.
If the power is cut, the freeze-protection valves open on their own, and that raises usage.

The rest of this guide assumes an individual gas boiler.

What the buttons on a Korean boiler controller mean

The labels are in Korean, but most brands use the same handful of words.
The behaviour behind each button differs by model, especially the cycle times for away and timer.
Published figures for those cycles disagree with each other, so treat any fixed number you read online, including on blogs, as model-specific.

Room mode or ondol mode?

Room mode reads the air at the controller, so a draft or a cold spot near it keeps the boiler firing.
Ondol mode reads the water temperature in the floor pipes instead.
KyungDong Navien has recommended room mode for a well-insulated home and ondol mode for a drafty one.
Rinnai has said room mode works when the controller is away from sun and heat sources, and ondol mode works better when it sits near a door that opens often, a draft, sunlight or an electric heater.

How you switch between the two modes differs by controller.
Search your controller's model number, which is usually printed on the front or the back, to find its quick manual.

How the city gas bill is calculated

Your meter measures gas in cubic metres (m³).
The supplier converts that into energy (MJ) and charges a rate per MJ.
One supplier publishes the residential formula this way:

(m³ used × temperature-pressure correction factor × average heat content in MJ/m³ × rate per MJ + basic charge) × 1.1

The 1.1 is the 10% VAT.
The correction factor adjusts for gas temperature and pressure, and that supplier says it is revised each March.
The heat content is an average figure set by the supplier.
Both values are usually printed on your bill.

A worked example with Seoul City Gas rates

Seoul City Gas's official rate table dated 2026-10-01 lists 22.5268 won per MJ for residential heating and a basic charge of ₩1,250 per month.
The usage figure and the two conversion factors below are round illustrative numbers, not real readings.
Replace them with the ones on your own bill.

Rate and basic charge from Seoul City Gas's official table, checked October 2026; the bill itself may round the last digits.

Two things follow from the arithmetic.
The basic charge is tiny, so almost the whole bill is MJ times the rate.
You can't change the rate, but you can change how many MJ you use.

Why your friend's bill uses different numbers

Unit rates vary by region and by supplier, and they change whenever wholesale or supply-cost rates are adjusted.
Seoul sets one unified retail rate across its gas companies, so within Seoul your supplier matters less than in other regions.
Outside Seoul, suppliers publish their own rate tables, sometimes with extra rules for households that use gas for both cooking and heating.
To find your real rate, look for your supplier's name on the bill and open its rate table (usually under a menu like "rates").

Reading the bill line by line

Most residential bills carry the same items, though the layout varies by supplier:

• Customer number. Have this ready when you call the supplier. If the bill is in your landlord's name, it is still the number they need.

• Previous and current meter readings. The difference is your m³ for the period.

• Correction factor and average heat content. These turn m³ into MJ.

• MJ used. Multiply this by the rate on your supplier's table.

• Basic charge, usage charge, VAT. These add up to the total due.

• Reading and billing period. This shows which days the bill covers.

Reading cycles and methods differ by supplier.
If a winter bill looks wrong, first check that the current reading matches what your meter shows.
An estimated or misread figure is the most common thing you can actually dispute.

Supplier websites and apps are generally in Korean only, and some features ask for Korean phone verification.
If you can't get through, the bill's customer number and a photo of your meter are enough for a Korean-speaking friend or your landlord to sort it out by phone.
Some suppliers also offer welfare discounts for eligible households.
Ask the supplier whether yours qualifies.

Settings that lower the bill without freezing the pipes

The idea that you should "never turn the boiler off" is half right.
Switching the power off is risky in a freeze because freeze protection stops with it.
Letting a cold home fall to the low teens and reheating it is also expensive, because reheating takes more energy.
How you lower the setting depends on how long you'll be gone.

Guidance compiled from boiler makers and heat-supplier statements reported in 2024 and 2025.

Government winter guidance targets an indoor temperature of 20°C.
Each 1°C lower cuts heating energy by about 7%.
Socks, a cardigan and a lap blanket do more than they sound like they would: warm clothing can make 20°C feel like 23–24°C.
Window film, door draft strips and a rug cut heat loss.
Running a humidifier while heating is also part of the official advice.

If you smell gas

City gas (LNG) is lighter than air and collects near the ceiling first.

1. Don't touch any switch, including lights, fans and the extractor hood. Switching anything on or off can spark.

2. Don't light anything.

3. Close the gas cock on the appliance and the intermediate valve on the pipe, then the main valve if you can reach it safely.

4. Open windows and doors.

5. Get out, then call from outside: 119 if there is any danger, or your supplier's customer centre (the number is on the bill or its website).

The Korea Gas Safety Corporation's main number, for general enquiries, is 1544-4500.
After a leak, don't use gas again until the supplier or a licensed technician has checked the installation.

Carbon monoxide from the boiler flue

A gas boiler vents its exhaust through a flue pipe.
Between 2017 and 2021, gas boiler accidents caused 46 casualties, including carbon monoxide poisonings.
The most common cause was an exhaust connection that had come loose.

Early poisoning feels like a cold or flu: headache, dizziness, nausea.
Severe cases lead to loss of consciousness.
If you notice these symptoms at home, ventilate right away, and call 119 if they don't improve, as fire services advise.

• Install a carbon monoxide alarm near the boiler.

• Look at the flue pipe: a joint that has come loose leaks exhaust, and a dented or blocked pipe is dangerous too.

• Have the boiler checked at least once a year by your gas supplier or the boiler maker.

Safety inspections at your door

City gas suppliers send inspectors to check household gas facilities.
Under rules revised by the Korea Gas Safety Corporation, households in most supply areas can do a self-inspection instead from May 2026, following the supplier's guide and reporting the results.
Ask your supplier whether it offers this.
If someone at the door says they are a gas inspector and you weren't expecting them, call the number on your bill and confirm before letting them in.