Which WELTEM Model Fits Your Space? Heater Sizing Guide

Choosing the right infrared heater is mostly about one thing: matching the heater’s output to the size of your space. Pick one that is too small and it will run flat out without ever getting comfortable; pick one that is far too big and you pay for capacity you never use. This guide walks you through how to size a WELTEM diesel infrared heater the easy way, and which of the five models fits your building.

Think in volume (m³), not floor area

A common mistake is to size a heater by floor area (m²). Heat fills a space in three dimensions, so what really matters is volume — length × width × height. A workshop with a 3-metre ceiling and one with a 6-metre ceiling can have the same floor area but very different heating needs.

To estimate your volume, multiply the floor area by the ceiling height. A 200 m² workshop with a 4-metre ceiling is 800 m³. That single number is the best starting point for choosing a model.

Three things that change the answer

Volume gets you close, but three factors fine-tune the choice:

Insulation. A well-insulated, sealed unit holds heat far better than a draughty shed with open doors. Poor insulation means you should size up.
Ceiling height and openness. Tall, open or frequently opened spaces lose heat quickly. This is exactly where infrared shines — it heats objects and people directly rather than the air — but it is still worth allowing extra capacity.
How you use it. Do you need to warm the whole space all day, or quickly take the chill off a work area? Infrared is excellent for fast, targeted “spot” warmth, which can let you choose a more modest model.

The WELTEM range at a glance

WELTEM Europe offers five diesel infrared heaters. Here is the quick overview:

Model	Output	Heats up to	Fuel use	Best for
WHO-070	8.1 kW	750 m³	0.72 l/h	Small workshops, garages, storage
WHO-095	12.8 kW	1,180 m³	1.2 l/h	Well-insulated garages & workshops
WHO-135	17.4 kW	1,600 m³	1.5 l/h	Medium workshops & warehouses
WHO-175	24.4 kW	3,660 m³	2.2 l/h	Large sheds & halls
WHO-250F	29 kW	4,680 m³	2.35 l/h	Large industrial spaces (with fan)

Matching a model to your space

Up to ~750 m³ — WHO-070. Ideal for smaller rooms: compact workshops, single garages, storage areas, site cabins and market stalls.
Up to ~1,180 m³ — WHO-095. A step up in power for well-insulated garages, workshops and showrooms that need steady, quiet warmth.
Up to ~1,600 m³ — WHO-135. The all-rounder for medium-sized work areas, warehouses and agricultural buildings where constant heat matters.
Up to ~3,660 m³ — WHO-175. High output for large sheds, storage halls and industrial units that need more reach.
Up to ~4,680 m³ — WHO-250F. The flagship, with a built-in fan for faster, wider heat distribution across large industrial halls, warehouses and event tents.

For very large or divided spaces, two smaller units often heat more evenly than one oversized heater — and give you flexibility to only heat the zone you are working in.

Get the most from your heater

Whichever model you choose, a few habits keep running costs down:

Use the thermostat rather than running continuously — real-world consumption is often 30–40% lower than the continuous-use figure.
Position it well so the heater radiates towards the area where people actually work.
Run it on (bio)diesel to lower your CO₂ footprint without changing anything else.

Still not sure?

If you would like a quick recommendation, tell us your space in m³ and how you use it, and we will point you to the right model — or try our heater finder for an instant suggestion. Every WELTEM heater is backed by a 3-year manufacturer’s warranty and supported locally by WELTEM Europe.

Find the right heater — fast