Anyone else finding their garden office impossible to heat in January?

Mine's basically a fancy fridge with a desk in it until the Victron kicks the underfloor heating into life around 9am — by which point I've already lost three fingers to frostbite and my best ideas have gone with them.

Went full overkill last autumn: 800W of panels on the roof, 200Ah of Fogstar Drift lithium under the floor, and a decent inverter, yet somehow January still finds a way to humble me. The problem isn't the power — it's the sheer thermal mass of a poorly insulated timber box that spent all night radiating heat into the Kent countryside.

Few things that've actually helped:

• Decent draught-proofing around the door frame (embarrassingly obvious but I ignored it for two years)
• A small oil-filled radiator on a timer set to kick in at 6am, so the space has a fighting chance before I arrive
• Reflective insulation behind the existing wall panels — bought a roll off Amazon for about £30 and it made a noticeable difference
• Sealing the gap around the cable entry points (mine was basically a wind tunnel)

Still not warm warm, but survivable.

Curious whether anyone's gone down the ASHP route for a garden office — seems like overkill for 20 square metres but I've seen a few people mention the Panasonic Aquarea mini units. Would love to know if the numbers actually stack up when you're pulling from batteries rather than the grid.

What's everyone else running? Surely I'm not the only one writing emails in a coat.

@KentCruiser welcome to the forum — glad you found us!

Genuinely feel this. My static caravan setup has the same "thermal lag" problem in deep winter — the space simply hasn't retained enough overnight heat for a 9am start to feel habitable.

A few things that helped me enormously:

• Pre-heat scheduling via Victron's ESS — I set mine to run a small oil-filled radiator from 06:30 using overnight cheap-rate power (Octopus Go here)
• Thermal mass matters — even a few dense rugs and bookshelves dramatically slow heat loss overnight
• Door draught sealing — embarrassingly simple but I lost maybe 15% of my heating load through gaps

The Victron GX device makes scheduled loads surprisingly straightforward once you're into the menus. Worth exploring if you haven't already — particularly the "scheduled charging" logic which you can repurpose effectively.

What's your current battery capacity?

@KentCruiser the 9am thing is a known pain point — your Victron is just doing sensible load-shifting but your fingers disagree with the logic.

What's your SOC set to trigger the heating? I dropped mine to kick in at 70% SOC rather than waiting for peak solar, and added a basic timer override so the office pre-heats 30 mins before I actually sit down.

Also worth looking at whether the insulation is the real culprit before blaming the system. My garden office was haemorrhaging heat through the roof until I added 100mm PIR board — made a massive difference to how quickly the Victron could actually maintain temperature rather than constantly playing catch-up.

A small thermal store can help too if you're on a decent battery bank. What size array are you running?

@KentCruiser the actual fix here is a pre-heat schedule rather than waiting for the Victron to decide conditions are right. On the CCGX or Cerbo you can set a scheduled charge window — I run mine to ensure the battery is topped up by 06:30, then have a small 400W panel heater on a mechanical timer kicking in at 07:00, well before I need the space. The underfloor is lovely but it's a thermal mass system — it needs 45-60 minutes minimum before you actually feel it. For emergency backup purposes I also keep a small 2kW propane cabinet heater (Gasmaster, bought from Toolstation) completely off-grid from the electrics entirely. Zero dependency on SOC, zero dependency on solar generation. January in the UK means consecutive grey days are absolutely coming, and your Victron will be throttling loads whether you like it or not.

@KentCruiser been there — my motorhome office suffered the same until I added a small 400W panel-heater on a Shelly plug with its own timer, completely independent of the Victron load management. Kicks in at 7:30am on a schedule, draws minimal overnight battery, and the main system never even notices it.

Worth checking your insulation before anything else though. A £15 thermal imaging camera hire from most tool shops will immediately show you where the heat's escaping — my setup was haemorrhaging warmth through a badly sealed cable entry point that took ten minutes to fix with fire-rated foam.

Also — are you running the underfloor on a Victron ESS schedule or purely on SOC triggers? If it's SOC-based in January you'll always lose that morning window. Switching to time-of-day control transformed my situation entirely.