Which bitcoin heater will keep my room warm?

The heat your room needs

need (W) = floor area (m²) × heat need (W per m²) × ceiling height ÷ 2.4 m

The heat need is a cold-day rule of thumb from heating guides in the UK, the US and Germany:

• Older and draughty: 150 W per m² (13.9 W per ft²)
• Typical: 100 W per m² (9.3 W per ft²)
• Modern: 60 W per m² (5.6 W per ft²)
• Very efficient: 40 W per m² (3.7 W per ft²)
• Passivhaus: 10 W per m² (0.9 W per ft²)

On milder days the same heater can keep a bigger room warm. A proper room-by-room heat-loss survey (BS EN 12831 in the UK and EU) will beat any rule of thumb.

Heat from a heater

Every watt a miner draws ends up as heat in the room, just like an ordinary electric heater. 1 W of power is 1 W of heat, or 3.412 BTU/h.

units to cover it = need ÷ the device's power, rounded up

We call anything under 300 W that can't cover the room on its own "top-up heat only".

Mining income

sats a day = hashrate (H/s) × 86,400 × average block reward ÷ (difficulty × 2³²) × (1 − pool fee)

The block reward is the 3.125 BTC subsidy plus the average fees of the last 144 blocks. This is what a mining pool pays on average. Mining solo usually pays nothing, and very rarely a whole block.

What the heat really costs

net cost a day = electricity a day − value of the sats

net cost per kWh of heat = net cost a day ÷ kWh used a day

heat pump cost per kWh of heat = electricity price ÷ heat pump efficiency

break-even efficiency (J/TH) = income per TH a day × 1,000 ÷ (24 × electricity price × (1 − 1 ÷ heat pump efficiency))

The season figures run the same heat through all three: a plain heater pays the full price, the bitcoin heater pays it minus the sats, and the heat pump pays it divided by its efficiency.

Honest caveats

• Difficulty tends to rise. More mining worldwide means fewer sats for the same heater, so income usually falls over time.
• The next halving, at block 1,050,000 (around Apr 2028), cuts the block subsidy from 3.125 to 1.5625 BTC. Mining income roughly halves overnight.
• The bitcoin price moves, both ways. Your sats can be worth more or less by the time you spend them.
• Heat is only useful in winter. Running it in summer means paying for heat you may then have to get rid of.
• Heat has to land where you need it. A miner that blows its warm air into a loft or out of a window gives you less useful heat.
• "Pays back vs a plain heater" is how long the sats take to match the price over your heating days, using the average bitcoin price (or the one you type), hashrate and block reward of the last 3 months, for the heat the room takes, with the subsidy cut at each halving. You'd pay for the electricity with a plain heater too, so it isn't counted, which also means the figure doesn't change with your electricity price. Neither is that heater's own price counted. "Never" means it doesn't get there within 30 years. How we work it out.
• These are estimates, not promises. They use rules of thumb, the maker's power figure, your tariff and live network data. Nothing here is financial advice.

Sources

• US EIA: 1 kWh of electricity is 3,412 BTU
• US DOE Energy Saver: an electric resistance heater turns all its electricity into heat
• UK electric radiator sizing: about 100 W per m², 130–150 W for poorly insulated rooms
• Sylvane space heater guide: about 10 W per sq ft with 8 ft ceilings
• Enpal (German heat-load guide): watts per m² by building age
• Baunetz Wissen: a Passivhaus heating load is at most 10 W per m²
• Heat Geek: why rule-of-thumb sizing is guesswork, and how rarely the coldest days come
• Energy Systems Catapult: UK heat pump field trial, median efficiency 2.8
• Luxor: how hashprice (mining income per unit of hashrate) is worked out
• Bitcoin Wiki: difficulty and the expected time to find a block
• Bitcoin Wiki: the block subsidy and halvings
• mempool.space API: live price, difficulty and block rewards

Live figures come from mempool.space and are kept for ten minutes. If they can't be reached, we use the figures saved when the site was built and say so.