The first question every grower asks about mining heat reuse is: "How much greenhouse can one miner heat?" The honest answer is that it depends on so many variables that a single number would be misleading. But that does not mean you cannot estimate usefully. You just need to work through the conversions and losses rather than relying on the back-of-napkin figures that circulate in mining forums.

This guide gives you the conversion factors, the loss multipliers, and the worked examples to translate mining hardware wattage into practical greenhouse heating coverage. It is not a replacement for professional thermal engineering on a large project, but for a small grower deciding whether one, two, or four miners can meaningfully contribute to heating a greenhouse, these calculations are what you need.

The Core Conversion: Watts to BTU/h

Every Bitcoin mining ASIC has a rated power consumption in watts. By the first law of thermodynamics, nearly all of that electrical energy converts to heat. A miner rated at 3,250 watts produces approximately 3,250 watts of thermal output. The hash computation is just the mechanism; the end product, thermally speaking, is heat.

The conversion factor:

  • 1 watt = 3.412 BTU/h (British Thermal Units per hour)

So a 3,250-watt miner produces roughly:

  • 3,250 x 3.412 = 11,089 BTU/h

For reference:

  • A small portable electric heater: 1,500 W = 5,118 BTU/h
  • A single S19 XP class miner: 3,010 W = 10,270 BTU/h
  • A single S21 class miner: 3,500 W = 11,942 BTU/h
  • A T21 class miner: 3,276 W = 11,178 BTU/h

Important nuance: the wattage figure from the manufacturer is the wall power draw. Actual consumption varies with ambient temperature, power supply efficiency, and whether the miner is running at stock settings, overclocked, or underclocked. Expect plus or minus 10 percent in practice.

From BTU/h to Heating Capacity

BTU/h tells you how much thermal energy the miner produces per hour. To know whether that is useful for your greenhouse, you need to compare it against the greenhouse's heat loss rate.

Heat loss from a greenhouse depends on:

  • Surface area of the glazing and walls
  • Insulation value (U-value) of the covering material
  • Temperature differential between inside and outside (delta-T)
  • Air exchange rate from ventilation, leaks, and intentional openings

Simplified Heat Loss Formula

Heat loss (BTU/h) = Total surface area (sq ft) x U-value (BTU/h/sq ft/degree F) x Delta-T (degrees F)

Or in metric: Heat loss (W) = Total surface area (sq m) x U-value (W/sq m/K) x Delta-T (K)

Typical U-Values for Greenhouse Coverings

Covering Material U-value (W/m2/K) U-value (BTU/h/ft2/F)
Single-layer glass 6.0 - 6.5 1.06 - 1.15
Double-layer glass 3.5 - 4.0 0.62 - 0.70
Single polyethylene film 6.5 - 7.5 1.15 - 1.32
Double polyethylene (inflated) 3.5 - 4.5 0.62 - 0.79
Polycarbonate twin-wall (6mm) 3.5 - 3.7 0.62 - 0.65
Polycarbonate twin-wall (16mm) 2.3 - 2.7 0.41 - 0.48

These values assume still-air conditions. Wind increases effective heat loss significantly, sometimes by 30 to 50 percent in exposed locations.

Worked Example 1: Single Miner, Small Greenhouse

Setup:

  • Greenhouse: 3m x 5m footprint, 2.5m ridge height
  • Covering: 6mm twin-wall polycarbonate (U-value: 3.6 W/m2/K)
  • Location: temperate climate, winter night low of -5 degrees C
  • Target internal temperature: 10 degrees C (frost protection for overwintering stock)
  • Delta-T: 15K
  • Miner: one S21-class unit at 3,500W

Approximate greenhouse surface area:

  • Two long walls: 2 x (5m x 2m average height) = 20 m2
  • Two end walls: 2 x (3m x 2m average height) = 12 m2
  • Roof (gable approximation): 2 x (5m x 1.8m) = 18 m2
  • Total: approximately 50 m2

Heat loss calculation:

  • 50 m2 x 3.6 W/m2/K x 15K = 2,700 W

Miner thermal output: 3,500 W (before delivery losses)

Delivery efficiency (accounting for duct losses, as covered in our layout guide): assume 70 percent.

Delivered heat: 3,500 x 0.70 = 2,450 W

Result: A single miner nearly covers the heating demand of this small greenhouse on a moderately cold night. On milder nights (delta-T of 10K), it provides comfortable surplus. On the coldest nights (delta-T of 20K or more), you need supplemental heating.

This is the realistic picture. One miner does not fully replace conventional heating, but it provides meaningful base-load warmth for a small, reasonably insulated greenhouse.

Worked Example 2: Two Miners, Medium Greenhouse

Setup:

  • Greenhouse: 4m x 8m, 3m ridge height
  • Covering: double polyethylene (U-value: 4.0 W/m2/K)
  • Location: cold continental, winter night low of -15 degrees C
  • Target: 12 degrees C (active growing, not just frost protection)
  • Delta-T: 27K
  • Miners: two S19 XP units at 3,010W each (total 6,020W)

Approximate surface area: 85 m2

Heat loss: 85 x 4.0 x 27 = 9,180 W

Delivered heat (at 65% efficiency for longer duct run): 6,020 x 0.65 = 3,913 W

Shortfall: 9,180 - 3,913 = 5,267 W

Two miners cover only about 43 percent of the heating demand in this scenario. That is still useful. It reduces your conventional heating bill by nearly half. But you absolutely need a backup heating system, and it needs to be sized for the full load because mining hardware can go down unexpectedly.

The Square Metre Reference Table

For quick estimation, here is how many square metres of greenhouse floor area a single miner can heat, assuming moderate insulation (twin-wall polycarbonate), 70 percent duct delivery efficiency, and frost protection only (delta-T of 15K):

Miner Class Wall Power (W) Delivered Heat (W) Approx. Coverage (m2)
S19 XP 3,010 2,107 12 - 15
S19k Pro 2,760 1,932 10 - 13
S21 3,500 2,450 15 - 18
T21 3,276 2,293 14 - 17
S21 XP 3,150 2,205 13 - 16

Caveat: These are rough estimates for planning purposes. Your actual coverage depends on your specific greenhouse construction, wind exposure, ground insulation, and how tightly the structure is sealed. Treat these as starting points, not guarantees.

Loss Factors You Must Account For

The raw wattage-to-BTU conversion is the easy part. The losses between the miner and the plant canopy are where planning gets real.

Duct Transfer Losses

  • Short run (under 3 metres), insulated: 10 to 15 percent loss
  • Medium run (3 to 6 metres), insulated: 15 to 25 percent loss
  • Long run (6 to 10 metres), insulated: 25 to 35 percent loss
  • Any run, uninsulated: add 10 to 20 percent additional loss

Distribution Losses

  • Well-designed under-bench distribution: 5 to 10 percent
  • Single overhead outlet: 15 to 25 percent (due to stratification)
  • Perforated duct at bench level: 5 to 15 percent

Intermittent Operation Losses

If your miner is not running 24/7, your average heat delivery is proportionally reduced. Mining hardware restarts are not instant; expect 5 to 15 minutes of ramp-up after a power cycle before full thermal output resumes.

When the Numbers Do Not Add Up

Sometimes the calculation tells you what you do not want to hear. If your greenhouse needs 8,000 watts of heating and you can only deploy 3,000 watts of mining heat, the system is a supplement at best. That is still worthwhile if you would be mining anyway. It is less worthwhile if you are buying mining hardware primarily for heating, because a 3,000-watt electric heater costs a fraction of what a 3,000-watt ASIC costs.

The economic logic of heat reuse only works when:

  • You are mining for the Bitcoin revenue and treating heat as a byproduct
  • The heat delivery infrastructure cost is modest relative to the heating fuel savings
  • You have a genuine, sustained heating need that aligns with mining operation hours

For the broader economics and decision framework, see Bitcoin Mining Heat Reuse. For layout specifics, see Bitcoin Mining Greenhouse Heating in 2026.

FAQ

Can I use this for cooling calculations in summer? Not directly. Summer cooling is a fundamentally different problem. Mining heat in summer is a liability, not an asset. See our coverage of summer mode operations for that side of things.

Do immersion-cooled miners change these numbers? The thermal output is similar (same wattage in, same heat out), but the delivery mechanism is different. Immersion systems output heat through a liquid loop, which can be more efficient for transfer but requires different infrastructure. The raw kW-to-BTU conversion remains the same.

What about thermal storage? Buffer tanks and thermal mass can smooth out the delivery timing, letting you store heat during the day and release it at night. This does not change the total thermal energy available, but it changes when it is available. Useful for operations where mining runs during cheaper electricity periods.