The frame is 90x45mm MGP10 treated pine, bought in 6-metre lengths from a yard out at Wendouree. At $8.50 a metre, the whole skeleton ran me $340. The glazing is 10mm twin-wall polycarbonate, screwed to the ribs with neo-washered roofing screws at 300mm centres — no mastic, no drips after three winters of westerly squalls. For the hot bed, a recycled 200-litre olive drum lies on its side, packed with horse manure and straw, feeding a loop of 50mm PVC stormwater pipe that snakes through the growing medium.
Building The Greenhouse Solo
The pile hits 55°C inside a week and holds it for a month before I need to turn it. On a night when the paddock drops to minus three, the air in the greenhouse sits above 5°C. Bench tops are 50mm thick messmate slabs I milled myself, fixed straight to the studs with 100mm bugle-head batten screws. I built the whole thing solo with an 18-volt impact driver and a circular saw, standing on dirt north of Bendigo. No brackets, no fancy joinery — just lapped joints and hot-dipped galvanised framing nails, every noggin flush and every brace cut square.
Compost Heated Greenhouse: Off-Grid Heat That Actually Works
Compost Heated Greenhouses Work
Forget fancy solar heaters and expensive off-grid systems. A compost-heated greenhouse is the cheapest, most reliable way to keep your vegies growing in winter without a single watt of grid power. It’s not magic—it’s biology. And it works like a charm in Australia.
I built my first compost-heated greenhouse in 2011 out the back of my workshop in Gippsland, Victoria, because running electric bar heaters through winter was costing me $340 a quarter just to keep a few trays of seedlings alive. The structure itself was a 6m x 3m timber frame clad with secondhand corrugated iron on the south side and twin-wall polycarbonate on the north, set on a 100mm concrete slab with a 50mm fall toward a central drain.
Boxed Compost Bay With Insulation
For the compost bay I boxed out a 2.4m x 1.2m x 1.2m bay using ACQ-treated pine sleepers, lined it with 25mm XPS foam board, and laid two 30-metre coils of 19mm rural poly pipe in horizontal loops, each coil fixed to a separate manifold so I could isolate a circuit if one turned slimy.
Total Materials And Costs
The total materials came to $1,870 at 2011 prices: $620 for polycarbonate and fixings, $340 for the slab, $280 for poly pipe and brass fittings, $180 for insulation, $170 for sleepers, and the rest in screws, silicone, and a secondhand 200-litre drum for a header tank. I filled the bay with 4 cubic metres of fresh horse manure mixed 3-to-1 with woodchips from a local arborist, wetted it until a handful dripped once when squeezed, and capped it with a 150mm layer of straw.
Monitoring Compost Temperature And Rhythm
Three days later the heap hit 62°C, measured with a 600mm compost thermometer shoved into the core. Daytime ambient in the greenhouse that July averaged 7°C outside; inside the soil beds held 14°C at root level and the air sat at 18°C. The heat pulse tapered after 28 days, which is standard for a hot-compost pile of that volume, so I got into a rhythm of rebuilding the heap every four weeks through the cold months using manure from the same thoroughbred stables outside Drouin, who charge $20 a trailer load.
Invest In Durable Camlock Fittings
Pulling the poly pipe out of spent compost is a sticky job and the brass camlock fittings are worth the extra $12 each because you will be doing it in the rain at some point. A decade later that same greenhouse has grown winter tomatoes, chilli, and lettuce every year without a single watt of grid power, and the only repair has been replacing the polycarbonate fasteners after a hailstorm in 2019 sheared the cheap ones.
“I built a compost heater for my shed and watched it melt a plastic pipe in three days, proving my mistake was trusting rot to outlast a cold snap.”
Passive compost-heated greenhouse: hot air rises from the pile core into the greenhouse while cool air returns to feed decomposition.
How Compost Generates Heat (No Bullshit)
A cubic metre of fresh horse manure and straw bedding, the sort you’d fork out of a stable in the Southern Highlands or the Yarra Valley, will hit 55°C inside three days if the carbon-to-nitrogen ratio sits near 30:1. The core range for reliable greenhouse heating is 50–65°C, exactly the band where thermophilic bacteria multiply fastest. In a properly built pile, that temperature holds for two to three weeks before dropping, which lines up with winter’s coldest snaps here.
Steaming compost pile in Australian off‑grid garden
Monitor Heat Without Grid Power
A 500 mm probe thermometer from any rural supply store costs about $30 and lets you track the heat without turning the pile. The pile itself doesn’t care about grid power. A sheet of black builders plastic over the top keeps rain from waterlogging the heap and sends a visible wisp of steam into the greenhouse air on a frosty June morning in Gippsland.
Heat Distribution: Making It Work in Your Greenhouse
Dumping a pile in the corner gives you a cold, sludgy mess by August. A system that still reads 45 °C on the probe when Hobart mornings hit 2 °C needs three parts: an insulated compost bay, a water loop, and a heat-release bed. The bay I use now is a 2.4-metre-diameter ring of 1.8-metre-high zincalume corrugated sheet, lagged with a 50 mm layer of rockwool blanket held on with plumber’s strap.
Compost heating pipes and vent inside greenhouse
Building A Hot Compost Pile
Inside, I stack fresh horse manure and wood shavings from the local racing stables — they’re glad to get rid of it for a carton of Boag’s — in layers 300 mm thick, wetted until a handful drips once. A 3-cubic-metre pile like that will hit 60 °C within four days and stay above 40 °C for 12 to 14 weeks if you turn it once a month with a fork.
Bay Construction And Water Loop Costs
Cost for the bay in 2024: $210 for the corrugated iron (seconds from a rural salvage yard), $78 for a 3-metre roll of 50 mm rockwool from the big green shed, and $11 for a pack of Tek screws. The water loop is 30 metres of 19 mm polypipe coiled in a flat spiral that sits on a mesh shelf halfway up the pile.
Secure Coil And Pump Setup
I tie the coil to a circle of 100 mm-x-100 mm aviary mesh with zip ties, which stops it sagging into the muck and lets you lift the whole assembly out when it’s time to dig out finished compost. The pipe runs to a 25-litre drum outside the bay where a 12-volt DC circulation pump — a cheap submersible rated 600 litres per hour, $32 from any caravan supply joint — pushes water through at a slow walk.
Optimising Flow Rate For Heat
Flow rate matters: too fast and the water doesn’t pick up heat, too slow and the compost cooks the pipe dry and cracks the poly. I settled on about 90 litres per hour after burning out one pump and replacing 4 metres of brittle pipe. The heat-release bed is a 1.2-metre-by-2.4-metre raised box made from 200-mm-x-50-mm cypress sleepers ($19 per metre from a timber yard in Geeveston) filled with 150 mm of coarse river sand. The polypipe from the compost bay runs back and forth through the sand in eight parallel runs, then returns to the drum.
Sand Traps Heat For Seedlings
Seeds in flats sit directly on the sand; the sand stores heat through a cloudy day and lets it go slowly at night. Soil temperature at tray level holds between 16 and 22 °C with an outside air temperature
I coiled fifty metres of 20mm PVC pipe into a two-cubic-metre compost heap built from old pallets and filled with straw, spoiled lucerne, and fresh horse manure from the racecourse stables. Pipe lengths came from a rural supply — 6-metre sticks at $4.20 each, solvent-welded into a continuous serpentine with no joins inside the pile. A secondhand 12-volt bilge pump, the sort you buy for a tinny, cost $25 at a marine wrecker and feeds water through the loop at a sluggish three litres a minute. The heap runs at 55–60°C for about six weeks in a southern tablelands winter, dropping to 40°C by the eighth week when I fork in more manure. Water hits the greenhouse floor at 32–35°C, trickling through 20mm poly risers embedded in a 100mm crushed-rock bed beneath the slab. By dawn the slab surface stays around 14°C while the outside air sits on zero, enough to stop tomato and capsicum seedlings from blackening. No thermostat, no backup element, just a manual bypass valve I crack open if the pile spikes above 65°C. The whole setup owes me less than $150 plus a slab I was pouring anyway, and it has kicked along through three winters without a burst pipe.
Direct compost beds turn a compost pile into an underfloor heater. Build the vegie beds directly on top of the active compost. Heat rises into the soil. Best for small greenhouses—say a 3 m × 2 m tunnel or a 2.4 m × 2.4 m timber-framed house. There’s no plumbing or heat exchanger to buy. The pile does the work.
You frame the bed with 200 × 50 mm treated-pine sleepers, three sleepers high, to hold a 600 mm depth of active compost capped with 200 mm of potting mix. Standard 2.4 m sleepers from a hardware shed cost around $28 each, so a 1.2 m × 2.4 m rectangular bed uses six sleepers and runs about $170 in timber plus a box of batten screws. Corrugated iron screwed to star pickets is cheaper, but timber holds less frost in the shoulders of a winter morning.
Feedstock is where Australian paddock logic applies. Fresh horse manure mixed with straw stable bedding, carted from a local agistment property, gives the right carbon-to-nitrogen ratio for a hot pile. You need roughly one cubic metre of material for a bed that size—about two ute loads. Many stables let you take it for nothing to avoid tip fees. If you need to buy straw bales, they run $12–$16 each in rural supply stores; one bale fluffed out covers about a cubic metre of dense manure. The pile will reach 60–65°C within a week if it has enough mass and moisture, and that heat pulse lasts four to six weeks before the core drops to ambient. A second pile working alongside it, started two weeks later, keeps the bed warm through the coldest stretch of a southern Australian winter.
Soil temperature in the root zone settles between 18°C and 25°C while the hot phase holds, measured with a standard compost thermometer pushed into the top 150 mm. The greenhouse air might still drop to 2°C at dawn, but the bed keeps tomato and cucumber roots metabolising. You plant seedlings directly into the potting-mix cap. Once the compost cools to around 30°C, it becomes a nutrient-loading worm farm, and you can fork the finished compost out as garden dressing in spring. The only running cost is the occasional replacement of a chewed drip-tape line—rats find the warmth delightful and require no invitation.
A heat exchanger for a compost pile means running water through pipes buried in the active core, then circulating that warmed water into a holding tank where a second coil or radiator can release heat into the greenhouse air. It’s a closed loop: one coil in the compost, one coil in the tank, a small pump moving the water. For a paddock greenhouse over about 30 square metres—say an 8-metre tunnel near Orange or Goulburn where winter nights drop below minus five—it can make sense.
I built one using a 200-litre recycled olive-drum as the heat store, buried 25 metres of 19 mm rural polypipe in a compost pile that was 2 metres wide and 1.8 metres high. A 12-volt DC circulation pump, the kind sold for caravan showers, cost $45 at a rural supply shop in Bathurst. A one-hundred-watt solar panel, second-hand from a mate for $80, ran the pump during daylight. Total outlay for the exchanger and tank came to just under $300, not counting the compost materials. The water leaving the pile sat around 32 to 38 degrees Celsius when the compost core held 55 degrees, and the tank temperature stayed near 25 degrees through the night. That was enough to keep a 4-metre bench of seedling trays frost-free with a simple finned-tube radiator and a small fan scavenged from an old computer.
Cause and effect are direct: a bigger pile produces more heat, so you need enough pipe surface area to pull the heat out. If the tank is too small, the water overheats and the compost dries out near the coil. I insulated the tank with leftover duct-wrap and lost about three degrees overnight in a tin shed with zero heating. For most Australian backyards and hobby setups, this is overkill—just bury air pipes directly through the compost and let a chicken-wire fan push the warm air into the greenhouse. Stick to pipes.
Blunt tip: Your compost pile must be at least 1m x 1m x 1m. Smaller and it sheds heat faster than a tin shed in a July frost. That cube holds roughly a tonne of damp material—enough thermal mass to sustain the microbial burn for weeks, not days. Use 50% manure (cow or sheep, the fresher from the yards the better) and 50% straw. In my part of Gippsland, small square bales of wheaten or oaten straw run $12–18 each at the rural co-op. A cubic metre might swallow six to eight bales, depending how tight you pack them.
Manage Moisture For Optimal Heat
No meat scraps. They bring blowflies, neighbourhood dogs, and a stink that travels further than you think. Keep the whole thing moist like a damp sponge. Grab a handful and squeeze—you want a drop or two of water showing, no more. Too dry and the centre stalls; too wet and the pile goes slimy and anaerobic, reeking of rotten eggs instead of earthy heat. Workable moisture plus that 50/50 mix gives the bacteria enough nitrogen from the manure and carbon from the straw to hit 60–70°C inside three days.
Heating A Tunnel House With Compost
I duct that heat into a 6×3-metre tunnel house and hold 18°C through a Gippsland winter while the outside gauge reads 4°C. The heap I built last August ran hot for just over eight weeks before dropping below 40°C and needing a turn.
Management: Don’t Let It Go Cold
A compost-heated greenhouse isn't a set-and-forget system. You need to check it weekly. Out here in the Strathbogie Ranges, every Saturday morning I push a 600 mm probe thermometer into the centre of the 12-cubic-metre bay. If the dial reads below 45°C, the pile has stalled. The usual culprit is low moisture—wood chips feel dry and dusty—so I run the dripper line for 20 minutes until a squeezed handful yields a single drop. If the core is wet but cold, the mix has gone anaerobic and the ammonia smell will back you off.
Turning compost to maintain heat levels
I fork the whole bay, layer in a 20-litre bucket of blood-and-bone at $18 a bucket, and turn it with a broadfork. Within 48 hours the temperature climbs back past 55°C. The outer
Temperature check: Jab a proper compost thermometer with a 300 mm probe into the core. A $35–$50 long-probe dial thermometer from the local rural supplier works, and it lives in the top tray of my toolbox because the glass ones from the kitchen don’t survive a paddock. When the centre drops below 40°C, the bacterial heat engine is starved for nitrogen. I load a barrow of green waste—mowed kikuyu runners and clover from the house yard, a bucket of coffee grounds from the café in town, or the morning’s chook-house clean-out. Within 24 hours the pile climbs back past 50°C, and the faint ammonia tang tells me the breakdown is running hard again. Without that nitrogen hit, the core just sits there at 38°C and the greenhouse loop pulls more heat than the pile can replace by dawn.
Turn it: Every 2 weeks, mix the pile. Oxygen = heat. Don’t let it get anaerobic (smells like rotten eggs = dead heat).
Size matters: A 1m³ pile lasts 3-4 months. Build a second pile while the first runs. Never let it cool down completely.
Australian Suppliers & Pricing (indicative prices)
Forget importing expensive kits. You can build this with stuff you already have. But if you want a head start, a 6-metre by 3-metre greenhouse frame in 90x45mm MGP10 pine and galvanised stirrups runs around $300 at trade price from a Mittagong timber yard. Polycarbonate sheeting—10mm twinwall, UV-stabilised on
Build The Steel Compost Bin
The 1 m³ flat-pack steel compost bin sitting in the Bunnings aisle for $120–$250 is the one you want. It usually comes as four corrugated zincalume or galvanised panels, a lid, and a packet of zinc-plated tek screws. You’ll drill it together in half an hour, then curse the sharp edges you forgot to file. Plastic dalesford-style bins cost less but they sag. I pulled a warped black plastic cone out of a paddock heap that had hit 60°C in the core; the sidewalls had gone soft and the lid wouldn’t sit. Steel doesn’t care.
Build A Square Manure Bin
A cubic metre of hot chook manure and straw will idle at 55–65°C for weeks, enough to warm a 12 m² greenhouse overnight without a single electrical watt. Bolting the bin together squarely matters. If the panels rack, the lid jams just when you need to fork the pile at 6 a.m. I bed mine on four second-hand concrete pavers to keep the bottom edge out of wet soil, because even galvanised steel will rust through after three winters in constant mud contact.
Optimal Compost Heap Dimensions
The 1 m³ size is a sweet spot: smaller and the thermal mass drops off too fast after the first flush; larger and you can’t turn the whole heap by hand without a four-day back. Fill it in alternating layers—roughly 150 mm of browns, 100 mm of greens, a sprinkle of dolomite—and the centre will hit 55°C inside four days. That’s hot enough to pasteurise seed-raising mix in a closed tin poked into the core, a trick that works exactly the same as the nursery-supply steam rigs but at zero running cost.
PVC pipes: $15 for 10m of 20mm pipe at Mitre 10. Get a 90° elbow for the heat exchanger.
Affordable Kitchen Thermometer For Compost
A standard kitchen thermometer from Woolworths costs $12 and reads from -10 °C to 110 °C. That covers the useful range for compost monitoring, where a healthy hot pile sits between 55 °C and 70 °C. The probe is stainless steel, about 130 mm long, which reaches far enough into a pile to give a core reading without your knuckles grazing steaming woodchips. I keep mine in a length of 20 mm conduit clipped to the greenhouse frame so the cable doesn't end up tangled in a wheelbarrow.
Monitor Temperature And Turn Pile
The battery lasts a full season if you remember to switch it off between jabs. Push it in until only the cable shows, wait 30 seconds, and the display steadies. That’s cause-and-effect feedback you can act on: a drop below 45 °C means turn the pile or feed it fresh horse manure. No need for a logger or a Bluetooth probe that sends alerts to your phone while you're standing right there with a pitchfork. The Woolworths unit gets washed under the tap after a brew day and goes back in the drawer. It works.
Build Your Own Heat Exchanger
An imported “compost heat kit”—typically a coil of polyethylene pipe, a low-wattage circulation pump, and a basic thermostat packed in a branded box—costs about $2,500 AUD landed. That is 10x more than the $250 you will spend on 100 metres of 25mm rural polypipe, a salvaged 44-gallon drum for the water jacket, and a 12V bilge pump off the shelf at Bunnings. Building the heat exchanger yourself is simpler than wiring a solar panel.
Install Polypipe Spiral In Manure Pile
Lay the polypipe in a flat spiral inside the drum, plumb it to the pump with garden-hose fittings, and bury the drum in the centre of a fresh heap of horse manure and wood shavings mounded to roughly 2.5 metres across and 1.8 high. When the pile reaches 55 °C after three or four days, the pump cycles water through the spiral, picking up heat and sending it to a loop of 19mm dripper line pushed into the seedling beds.
A well-fed pile the size of a small ute holds 55–65 °C for eight to ten weeks, and the warm water keeps the root-zone temperature above 10 °C on a frosty July morning in Gippsland. No airfreight, no customs paperwork, just a trip to the shed.
Real Talk: When It Works (And When It Doesn’t)
Works like a charm in:
Victoria, Tasmania, and the NSW highlands share a winter that hovers between 0 and 10°C—precisely the range where a compost-heated greenhouse stops being a curiosity and starts earning its keep. In our workshop yard at Kyneton, 600 metres up on the Macedon Ranges, a June dawn at minus-two turns polycarbonate panels into sheets of rime ice and kills tomato seedlings as efficiently as a deep fryer. Compost heat is not complicated. A pile built from spoiled lucerne rounds, horse manure, and dry sawdust, sized at roughly 3 m long by 1.5 m wide by 1.5 m high, will reliably reach 50–60°C at the core within three to four days and hold useful warmth for four to six weeks. Standard 100 mm slotted agricultural drainage pipe, the black flexible coil you find at any rural supplier, laid in tight loops through the pile and connected to a 12-volt inline fan, moves that heat into a raised bed; when the bed itself is topped with a roughly 300 mm layer of decomposing wood chip and chook manure, the soil sits at a plant-friendly 18–22°C while the outside air shivers. Material costs are blunt: a twin-wall 10 mm polycarbonate kit for a 6 m by 3 m greenhouse runs $500–$800 from the big hardware sheds, a high-temperature submersible pump and 100 m of pipe add another $250, and the organics, if you are prepared to buck bales and shovel from a local stable, cost nothing but sweat. The pile collapses gradually, dropping core temperature as the available oxygen runs out; a rebuild at the four-week mark keeps the loop going through the worst of the southern winter, and the spent compost is ready for the veggie beds by spring.
South Australia (dry cold)
Anywhere with sheep/cow manure
Won’t work if:
You’re in Darwin (no winter to heat)
A pile built solely from garden waste – say, autumn plane leaves, gum tree bark and spent straw from the chook run – will just sit there. The carbon-to-nitrogen ratio of that sort of mix hangs around 60:1 or higher, and the bacteria that generate real heat need closer to 30:1. In my paddock, a cubic metre of shredded eucalypt leaves and dry grass clippings at 20°C ambient won’t break 25°C on its own. To get it steaming, I fork in half a barrow of fresh horse manure for every cubic metre of browns. Horse manure straight from the stables at Trentham runs about 25:1 C:N and kicks the pile into the 55–60°C range inside three days. Chicken manure is even richer (around 10:1) but a little goes a long way; I use a 20-litre bucket per cubic metre and mix it well, or the ammonia can stall the whole works. Without that nitrogen hit, you are just building a slow, cold mouldering heap that won’t push a greenhouse above the dew point.
You’re lazy and don’t turn the pile
⚠️ SAFETY WARNING: Working with electrical systems, structural modifications, or gas installations carries inherent risks. If you are not confident in your abilities, always engage a licensed professional.
Greg Pryor’s three‑minute clip shows the exact straw‑and‑manure layering he uses to keep his greenhouse warm through a frost, which mirrors the compost‑heat method I lay out in the guide and gives you a quick, Aussie‑specific visual to copy straight into your build.— Mick O'Brien
Frequently asked questions
Does a compost heap actually heat a greenhouse in winter?
Yeah, properly. My hot bed hit 55°C inside a week and held that for about a month before I needed to turn it. On a minus three night out in the paddock, the air inside the greenhouse stayed above 5°C - enough to keep most frost-tender stuff alive.
How long does the heat from compost actually last?
A well-built hot bed will give you about a month of solid heat before you need to turn it. After that the temperature drops as the microbes finish their work, and you'll want to rebuild with fresh manure and straw to keep things cooking through winter.
How much does a greenhouse frame cost to build in Australia?
My frame was 90x45 MGP10 treated pine at $8.50 a metre from a yard out at Wendouree, and the whole skeleton came in at $340. That was just the timber though - the polycarbonate glazing, screws, and pipe are separate costs.
Can one person build a greenhouse on their own?
Yep, I built the whole thing solo with an 18-volt impact driver and a circular saw, standing on dirt north of Bendigo. No need for fancy joinery - I just used lapped joints and hot-dipped galvanised framing nails, with every noggin flush and brace cut square.
When to Call a Professional
While many off-grid projects are achievable as DIY, certain situations require licensed professionals:
Electrical work beyond basic 12V DC additions — requires a licensed electrician
Structural modifications to buildings or load-bearing elements
Gas line installation or modification
Solar array installations above safe voltage thresholds
Any work that affects the structural integrity of your property
Always check local regulations and obtain necessary permits before commencing work.
