Sizing a wood burner for a small off-grid cabin — going smaller than everyone recommends?

I've been getting the cabin watertight over the past few months — it's a single-room timber frame build, roughly 5x4m, so about 20m² with maybe 2.4m ceiling height. Standard advice everywhere seems to be a 5kW stove minimum, but that feels massive for such a small space, especially since I've insulated fairly well (100mm Rockwool in the walls, 150mm in the roof).

Been looking seriously at the Hobbit stove (4kW) or even the Tiny Rebel at around 3kW. The cabin won't be lived in full-time — more like weekends and occasional longer stays, so I'm not trying to hold heat overnight, just get the space warm reasonably quickly from cold. It does drop to -5°C or so up here in the Peaks in winter.

Has anyone gone with a smaller stove in a well-insulated space and actually been happy with it? My worry with going too big is just constantly throttling it back, which kills efficiency and causes creosote buildup on a flue that's probably going to be a 5" twin wall anyway. The Hobbit in particular seems to get good reviews but I keep second-guessing myself.

Curious what people actually run in similar-sized spaces rather than what the heat loss calculators spit out.

@SamBaker interesting question — I've been thinking along similar lines for my narrowboat, where oversizing a stove is a real problem in a small space.

One thing worth considering: what's your insulation spec like? A well-insulated 20m² space behaves very differently to a poorly insulated one. Even a 4kW stove can feel excessive if you've got decent wall and roof insulation.

Have you looked at the Hobbit stove by Salamander? It's specifically designed for small spaces — 4kW nominal but quite controllable at lower outputs. Loads of narrowboaters and cabin owners use them.

The "go bigger for safety" advice often assumes worst-case insulation and construction, which may not apply to your build.

What's your wall U-value roughly, and are you planning to use it as occasional or full-time heating?

Great timing on this thread @SamBaker. For a well-insulated 20m² space you're almost certainly looking at 4kW or even 3kW being plenty — I'd actually argue a 3kW stove running properly at capacity will outperform a 5kW stove being throttled back constantly. The efficiency difference is significant, and you'll thank yourself when you're not cooking yourself out in spring and autumn shoulder seasons.

The key question is your insulation spec. What are your wall U-values like? A tightly built timber frame with decent mineral wool could legitimately need very little heat input once up to temperature.

Similar principle to @AshSeeker's narrowboat situation — confined spaces punish oversizing badly. Look at the Hobbit stove or the Chilli Penguin range, both designed specifically for smaller spaces and both have solid reputations on here.

Been down this exact rabbit hole with my van conversion — ended up with a 2.5kW Cubic Mini and honestly it's too much on cold nights once the space is warm. Thermal mass is the bit everyone ignores. Your timber frame walls will hold heat surprisingly well once you've been burning a couple of hours.

One thing worth factoring in @SamBaker — what's your door and window situation? I lost half my heat through a badly fitted skylight for three months before I worked it out. Embarrassing, really.

Also look at the Hobbit stove — made in the UK, properly rated for small spaces, and the 4kW model has a throat plate you can partially close to throttle it right down. Effectively gives you variable output without buying something underpowered.

@JohnDixon a 2.5kW being too much in a van — my motorhome runs a tiny 1.8kW unit and in winter I'm basically sat in my pants by 9pm wondering why I bothered with the Victron battery bank when I'm sweating through the solar charge controller.

Really useful thread this. @SamBaker one thing worth factoring in that often gets overlooked — thermal mass and how quickly you need the space to heat up. A 3kW unit in a well-insulated 20m² cabin will absolutely cook you out if you're running it hard for hours, but if you're arriving to a cold cabin on a Friday evening wanting heat fast, that extra output matters in those first 30-45 minutes.

Worth considering a unit with a good air-wash and damper control so you can choke it right back once you're up to temperature. Some of the Charnwood and Hobbit units are brilliant for this — technically 4kW but genuinely controllable down very low. Don't just chase the kW rating, look at the minimum burn rate too.

@SamBaker had similar debate sizing the burner for my garden office — ended up going 4kW and genuinely wish I'd gone 3kW. The thing roasts me out within 20 mins if I'm not careful.

Your 20m² with decent insulation? I'd say 3-3.5kW is the sweet spot. A 5kW will spend its whole life damped down, which is terrible for the flue — creosote buildup, poor draw, the works.

Look at the Hobbit stove by Salamander — properly sized for small spaces and built well. Charnwood Cove 1 is another worth considering if budget stretches.

Main thing people forget: insulation quality matters more than kW rating. What's your wall/roof spec like?

@SamBaker yeah go smaller than the calc suggests — similar situation in my motorhome, tiny space heats fast and you end up with the door open trying to cool down. A well-insulated 20m² with decent glazing will hit temp quickly.

Worth thinking about your heat-up pattern too — are you arriving cold and wanting rapid warmth, or is it occupied most of the time? Changes the logic a bit.

Also what flue run are you working with? A long straight run on a smaller burner can draft better than people expect.