Converted an old shepherd's hut last summer — still struggling to keep it warm in January

Anyone else find January is just when everything falls apart with a shepherd's hut build? I converted mine last summer and genuinely thought I'd cracked it — 100mm of Celotex in the floor, walls done with rockwool batts, the lot. Now it's -3° outside and my little Morso squirrel stove is working flat out just to keep it at 14°C inside.

Few things I'm not sure about:

• Thermal bridging at the chassis — those steel runners must be leaching heat out the bottom. Did anyone actually address this properly or just accept it?
• Door seals — the stable-style door on mine is basically a wind tunnel. What's people's go-to for draught-proofing without wrecking the aesthetic?
• Floor — is 100mm enough or should I have gone deeper?

Also wondering whether my Victron setup is partly to blame. Running a small ceramic fan heater overnight to supplement the stove but the 200Ah Fogstar lithium bank is struggling. Should probably have sized that bigger in hindsight.

Is this just a "shepherd's huts are draughty, deal with it" situation or have people actually cracked decent winter comfort in one? What insulation depths are others running and did anyone use a heat pump instead of a stove?

HollyGraham87 | 847 posts | ⚡ Solar & Wind Enthusiast

@BatteryPaddy Oh, the classic "summer build, winter regret" moment — been there! One thing people often overlook with shepherd's huts specifically is the chassis. All that cold steel underneath is basically a giant heat sink wicking warmth straight out through your floor, regardless of how good your Celotex is. Worth checking whether your insulation actually extends down around the frame itself or if there are any thermal bridges there.

Also — what's your heating setup? With the curved roof on a hut, warm air just pools up top and does nothing useful unless you've got some air circulation sorted. A small destratification fan can make a surprising difference for almost no energy cost. January in the UK is brutal for small metal-framed structures! Don't give up on it. 😊

SomersetVanLifer | 1,203 posts | ☀️ Solar & Shepherd's Hut

@BatteryPaddy The floor is where people consistently underestimate heat loss — 100mm Celotex sounds adequate but shepherd's huts sit on wheels/axles, meaning the underfloor void gets serious airflow underneath. That cold air movement strips heat far more aggressively than a ground-contact slab would.

What's your actual U-value calculation for that floor build-up? Also, what are you heating with? A lot of people run an undersized propane stove and wonder why they can't recover from a cold overnight.

My hut runs a Webasto diesel unit with a dedicated battery bank (Fogstar cells, Victron MPPT charging) — keeps thermal mass topped up overnight without burning through gas. The metal skin is your enemy in January regardless; thermal bridging through the chassis rail is real.

Post your wall section spec and I'll have a proper look.

HazelPaddy | 312 posts | ☀️ Solar & Batteries

@BatteryPaddy What's your heating source? That's often the missing piece people don't mention. I had similar issues until I realised my little diesel heater was fighting against cold air infiltration around the wheel arch openings — classic shepherd's hut weak spot that doesn't show up until genuine cold snaps.

Also worth checking: are your battery losses higher than expected in the cold? My Fogstar Drift cells drop noticeably in capacity below 5°C, which can mean the heating runs shorter cycles overnight than you're planning for. If you're running anything electric for heat, January will absolutely expose that gap.

What does your insulation look like at the roof apex? That's where I'd look after the floor points @SomersetVanLifer raised.

AshChild | 589 posts | ⚡ Narrowboat & Off-Grid Systems

The thermal bridging through the steel chassis rails is something nobody mentions — on a narrowboat it's the same problem with steel ribs, and it absolutely murders your heat retention overnight. Even with solid insulation elsewhere, those conduction paths will drag your interior temp down faster than you'd expect.

Worth doing a proper thermal camera survey on a cold night. Hire one locally or borrow through a tool library — you'll immediately see exactly where you're losing heat rather than guessing.

Also worth checking: what's your heating system's thermostat strategy? If you're running something like a small propane or diesel unit cycling on/off, you want it maintaining a baseline rather than reacting to temperature drops. Proactive not reactive — significant difference in perceived comfort and actual fuel consumption across a January week.

BitsAndBobs | 847 posts | 🔋 Garden Office & Van Dweller

@BatteryPaddy Had the exact same rude awakening with my garden office build — turns out January is basically the universe's way of invoicing you for every insulation shortcut you made in August when it was 24°C and optimism was cheap.

@AshChild makes a solid point on thermal bridging, but I'd also look at your ventilation gaps — shepherd's huts are notorious for moisture buildup that absolutely destroys your effective R-value overnight.

My garden office sorted itself properly only after I added a Propex HS2000 and stopped relying on a single electric panel heater running off my Fogstar lithium setup like it was a tropical spa.

What's your battery bank doing overnight — is it even keeping up with demand, or are you waking up to a Victron screen full of bad news?