FAQ
TL;DR: For a 35 m² detached garage, 8 cm EPS under-slab insulation can cut heat loss by ≈30 % [andrzej lukaszewicz, #13330513]. "Underfloor heating is the most economical" [wada, #11738249]. Choose PEX-16 (200 m) and 45–50 °C water to keep 7–10 °C inside. Why it matters: balanced comfort protects your car and tools while slashing fuel bills.
Quick Facts
• Heat load for a 35 m² garage held at +10 °C: approx. 1.5–2 kW [EN 12831].
• 200 m of PEX-16 pipe costs ~500 zł and covers 35 m² floor area [andrzej lukaszewicz, #13330513].
• EPS100 polystyrene, 8 cm thick, meets 0.38 W /m²K floor U-value target [andrzej lukaszewicz, #13330513].
• Salvaged copper heater core + fan can double panel-radiator output at the same flow [Piotr77777, #11736712].
• Heat-pump with SCOP 4 draws ~300 W to supply 1.2 kW heat at −5 °C [wesmar, #16929608].
Do I need to insulate a 35 m² brick garage before adding heaters?
Yes. A 10 cm external styrofoam layer lowers transmission losses enough to hold 7 °C with low water temperature [William Bonawentura, #11625728].
Which system is cheaper for a steady 7–10 °C: underfloor or wall radiators?
Underfloor wins. Pipe, insulation and screed cost about 30 zł/m², yet supply water can stay at 25–30 °C, cutting boiler cycling [wada, #11738249].
How thick should the insulation under the slab be?
Install at least 8 cm EPS100. This depth resists wheel loads and meets Polish garage U-value rules [andrzej lukaszewicz, #13330513].
What pipe length and spacing heat 35 m² evenly?
Lay 200 m of PEX-16 at 20–25 cm centres. Flow 2–3 L/min suits 45 °C supply [andrzej lukaszewicz, #13330513].
Can I use 16 mm PEX buried 20 m from the boiler?
Yes, but run twin PEX in a 110 mm PVC conduit and add 18/20 mm lagging to slash ground losses [daniel_lhr, #14249745].
What if the garage is used only occasionally?
Large concrete inertia delays warm-up. In that case oversize a fan-assisted radiator or use an electric radiant panel for rapid heat [Grzegorz Siemienowicz, #13374371].
Will under-floor pipes freeze in power outages?
Slope manifolds to a 170 cm deep valve so you can drain by gravity; no slope means trapped water can burst pipes [mscgs24, #11625745].
How much heat can a recycled car heater core deliver?
At 50 °C water and twin 30 cm fans it can provide 3–4 kW—about twice a 600 mm panel radiator [Piotr77777, #11736712].
How do I connect that heater core for best output?
- Replace the top bypass with a T-piece on the supply.
- Mirror on the return side.
- Bleed at the highest point.
This doubles wet surface and eases venting [saskia, #11743027].
Which diameter PEX supply line minimises hydraulic loss over 20 m?
PEX-20 × 2 mm gives ≈100 Pa pressure drop at 0.2 L/s, 40 % less than PEX-16, aiding small pumps [Jacek79, #14249808].
Do I need thermostatic valves?
Fit one on each emitter. At only 10 °C set-point they prevent overheating when sun warms the garage [Anonymous, #13276740].
Is a heat-pump air-conditioner viable for a garage?
Yes. A unit with SCOP 4.0 uses about 0.5 kWh to keep +10 °C at −5 °C outside, under 0.30 zł/h on night tariff [wesmar, #16929608].
