When heaters are running but the building stays cold, it is tempting to assume the heaters are too small or are faulty. Sometimes that is the answer, but often it is not. A warehouse can have perfectly adequate heaters and still feel cold because the heat is being lost, trapped in the wrong place or switched off too early by its controls. Before spending money on more heating, it is worth working through the common causes in order. Here they are, roughly from most to least common.

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One thing to bear in mind as you read: some causes apply to any heating system, while others depend on whether you have warm air or radiant heating. Stratification, for example, is a warm air problem, while a poorly aimed heater is a radiant one. The sections below note which is which, and there is a dedicated section on radiant-specific causes further down.

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1. The Heat Is Collecting at the Ceiling

 

This is the most common reason a warm air heated warehouse stays cold at floor level. Warm air is less dense than cold air, so it rises. In a tall building the warm air your heaters produce drifts straight up and collects in a layer at roof level, sometimes 10 to 15 degrees warmer than the air around the people working below. The heaters are working, the heat is being produced, it is just all sitting above everyone's heads.

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This is called stratification, and it is the single biggest hidden cause of a cold warehouse. The giveaway is a building that is warm if you climb up high but cold at floor level, and heaters that seem to run constantly without ever making the floor comfortable.

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The fix is destratification fans, which recover the warm air from ceiling level and push it back down to where people are. They are essential for any warm air heated building and typically pay for themselves within a single heating season. The Hadar DSF is designed for exactly this. We explain the problem in full in our guide on why destratification fans are essential.

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2. Heat Is Escaping Through Open Doors

 

If your loading doors are open for much of the working day, you may be losing heat as fast as the heaters can produce it. Every time a large door opens, warm air pours out and cold air floods in. In a busy warehouse with doors open for loading and unloading, this can overwhelm the heating completely, so the heaters run continuously while the building stays cold.

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The signs are a building that is noticeably colder near the doors and that warms up when the doors are closed for a period. The fixes include better door discipline, faster-acting doors that spend less time open, and air curtains over the openings. An air curtain such as the Sonniger Guard Pro projects a barrier of air across the doorway that dramatically reduces the heat lost while the door is open. We cover this in detail in our guide on loading doors and heating efficiency.

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3. The Heaters Are Undersized

 

Sometimes the heaters genuinely are too small for the building. This can happen if the building has changed since the heating was installed, for example if an extension was added, if insulation was removed or never adequate, or if the use of the building changed. It can also happen if the original system was simply specified too small.

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The telltale sign of undersized heating is a system that runs continuously, never reaches the target temperature even with the doors closed and no stratification problem, and falls further behind on the coldest days. If destratification is working and doors are not the issue but the building still cannot reach temperature, capacity may be the problem.

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The fix is to correctly assess the building's heat loss and provide adequate heating capacity, which may mean additional or larger heaters. Modern high-efficiency units like the Apen LKN can deliver more heat for less fuel than older equipment, so upgrading undersized old heaters can solve the capacity problem and cut running costs at the same time.

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4. The Building Is Losing Heat Too Fast

 

A warehouse with poor insulation, single-skin cladding, gaps in the structure or failed door seals loses heat continuously through its fabric. If the building loses heat faster than the heaters can replace it, it will stay cold no matter how hard the heating works. This is closely related to undersizing, because a leaky building effectively needs far more heating than a well-sealed one of the same size.

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Signs include cold draughts, condensation, and a building that loses heat very quickly once the heating switches off. The fixes range from quick wins such as sealing gaps, fixing door seals and addressing obvious draughts, through to larger projects such as improving roof and wall insulation. For a warm air heated building, radiant heating can also be a better answer in a poorly insulated space, because it warms people and surfaces directly rather than trying to keep a leaky volume of air warm.

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5. The Controls Are Wrong

 

Sometimes the heaters stop heating too early because of how the controls are set or positioned, even though the building is not yet warm where it matters.

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• Thermostat in the wrong place:A thermostat positioned in a warm spot, such as near a heater, high on a wall in the warm layer, or in an office, will register the target temperature and switch off the heating while the working areas are still cold

• Set point too low:A thermostat set lower than people realise will hold the building at that lower temperature, which can feel cold for the activity taking place

• Poor or no zoning:A single control for a large building cannot account for different areas with different needs, so some areas are left cold while others are satisfied

• Schedule too short:If the heating is scheduled to start too late, the building never has time to reach temperature before people arrive, and a large cold building takes a long time to warm up

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Checking that thermostats are sensibly located, correctly set and that the heating schedule gives the building enough time to warm up is a no-cost first step that often makes a real difference.

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6. The Heaters Are Not Performing

 

Finally, the heaters themselves may not be delivering their rated output. A heater with blocked filters, a dirty heat exchanger, a burner that is out of tune or a failing fan produces less heat than it should while still appearing to run. Several underperforming heaters across a building add up to a building that cannot reach temperature.

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The signs are heaters that are clearly running but feel weak, uneven heating across the building, or a gradual decline in performance over time. The fix is servicing and maintenance to restore the heaters to their rated output. Our warm air heater maintenance guide explains what a service should cover and the warning signs that a heater needs attention.

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7. Radiant-Specific Causes

 

If your warehouse is heated by radiant heaters rather than warm air, some of the causes above do not apply. Radiant heating does not stratify in the same way, because it warms people and surfaces directly rather than heating the air, so a cold radiant-heated building is rarely a stratification problem. Instead, radiant heating has its own specific reasons for leaving a building cold:

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• Poorly positioned or aimed heaters:Radiant heat travels in the direction the heater faces. If heaters are aimed at the wrong area, or at gaps between working positions, the heat lands where nobody benefits from it. Repositioning or re-aiming the heaters can solve this

• Mounted too high for the output:Radiant heaters are designed to be mounted within a range of heights for their output. Mounted too high, the heat spreads too thinly by the time it reaches floor level. The fix is the right heater output for the mounting height, or correct mounting height for the heater

• Too few heaters or wrong coverage:Radiant heating warms the areas it covers. If there are too few heaters or they are spaced to leave cold gaps, parts of the building stay cold. The fix is correct coverage for the working areas

• Dirty reflectors and emitters:Radiant output depends on clean reflectors and emitters. Coated in dust and dirt they deliver far less heat. Cleaning restores the output, as covered in our radiant heater maintenance guide

• Wrong heater type for the building:Some radiant heaters suit some buildings better than others. A heater poorly matched to the space may never deliver comfortable warmth where it is needed

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Radiant heating is often the better answer in buildings where warm air struggles, such as tall, draughty or poorly insulated spaces, because it does not rely on keeping a large volume of air warm. If a warm air system is failing to heat a difficult building, switching to or adding radiant heating can be the real fix rather than simply adding more warm air capacity. Our guide on radiant vs warm air heating explains where each works best.

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How to Work Through It

 

To diagnose a cold warehouse, work through the causes roughly in this order. First, the causes that apply to any heating system:

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• Check the doors:Is it colder near open doors, and warmer when they are shut? If so, address door losses with discipline, faster doors or air curtains

• Check the controls:Are thermostats sensibly placed and set, and does the schedule give enough warm up time? This is the cheapest thing to fix

• Check heater performance:Are the heaters serviced and delivering their rated output, with clean filters and reflectors?

• Check the fabric:Is the building losing heat through poor insulation, gaps or failed seals?

• Consider capacity:If everything else is right and the building still cannot reach temperature, the heaters may be undersized

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Then the cause that depends on your heating type:

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• If you have warm air heating, check for stratification:Is it warm high up but cold at floor level? If so, destratification is the answer

• If you have radiant heating, check positioning and coverage:Are the heaters aimed at the working areas, mounted at the right height and clean? If not, repositioning, re-aiming, cleaning or correcting the coverage is the fix

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Working through in this order means you address the cheapest and most common causes first, and only consider spending on more heating capacity once the other possibilities have been ruled out.

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Where to Start

 

A cold warehouse despite the heating running is almost always fixable, and often without buying more heating. The key is to diagnose the real cause rather than assuming the answer is bigger heaters.

Hadar Industries can assess your building, identify why it is staying cold and recommend the right fix, whether that is destratification, air curtains, controls, servicing or additional heating. Contact us today for a free site survey.

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Frequently Asked Questions

 

Why is my warehouse cold even though the heaters are running?

 

The most common reason is stratification, where warm air rises and collects at the ceiling instead of reaching floor level. Other causes include heat escaping through open doors, undersized heaters, a building that loses heat too fast through poor insulation, controls set or positioned wrongly, and heaters that are not performing to their rated output. Stratification is the most common single cause.

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Why is my warehouse warm at the top but cold at the bottom?

 

This is stratification. Warm air is less dense than cold air, so the heat your system produces rises and collects in a layer at roof level, leaving the floor cold. The fix is destratification fans, which recover the warm air from high level and push it back down to where people work.

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Can open doors stop a warehouse from heating up?

 

Yes. Large doors open for much of the working day let warm air pour out and cold air flood in, which can overwhelm the heating so the heaters run continuously while the building stays cold. Door discipline, faster-acting doors and air curtains all reduce this heat loss.

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How do I know if my heaters are too small?

 

Undersized heating runs continuously, never reaches the target temperature even with the doors closed and no stratification problem, and falls further behind on the coldest days. If destratification is working and doors are not the issue but the building still cannot reach temperature, capacity may be the problem and the building's heat loss should be properly assessed.

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What is the cheapest thing to check first?

 

The controls. A thermostat positioned in a warm spot or set too low will switch the heating off while the working areas are still cold, and a heating schedule that starts too late never gives a large building time to warm up. Checking that thermostats are sensibly located and set, and that the schedule allows enough warm up time, costs nothing and often helps.

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Why is my radiant-heated warehouse cold?

 

Radiant heating does not stratify like warm air, so a cold radiant-heated building is usually down to the heaters being poorly positioned or aimed away from the working areas, mounted too high so the heat spreads too thinly, too few in number to cover the space, or with dirty reflectors and emitters that reduce output. Repositioning, re-aiming, cleaning or correcting the coverage usually fixes it.