The complaint arrives in the same shape every time. Someone replaces an ageing vented dryer with a shiny A+++ heat pump model, loads it with towels, and watches the display announce three hours and forty minutes. The old machine did the same load in ninety. Something must be wrong.
Usually nothing is. Heat pump dryers are slower, and the gap is bigger than most retailers explain at the point of sale. But there's a line between "slower by design" and "something needs cleaning", and knowing where it sits saves an unnecessary engineer visit.
The Short Answer
A heat pump dryer running a full 8kg cotton load in two and a half to three and a half hours is behaving normally. That's what low-temperature drying looks like. If cycles have crept up over months, or clothes come out damp at the end, the cause is almost always the secondary filter — the sponge or mesh filter behind the kickplate at the bottom of the machine, which a great many owners don't know exists.
Clean the door filter after every load, and rinse the lower filter every month or two. If a machine that used to take three hours now takes five, that lower filter or the condenser fins behind it are blocked with lint about nine times out of ten.
What Actually Matters
A vented or condenser dryer heats air with an element to around 70–80°C and drives it through the drum. Hot air holds a lot of moisture, so drying is fast. It's also energy-hungry and hard on fabrics.
A heat pump dryer runs a refrigerant circuit instead. Air is heated to a much gentler 50–60°C, passed through the load, then cooled so its moisture condenses out, then reheated and recirculated. The energy recovered from that condensation is reused rather than thrown away, which is why running costs are roughly half those of a condenser dryer. But cooler air carries less moisture per pass, so it has to make more passes. The time is the price of the efficiency.
The practical consequence is that anything restricting airflow hurts a heat pump dryer far more than it would a vented one. A vented dryer with a partly blocked filter still has thermal headroom. A heat pump machine is already working at the margins, so a layer of lint on the evaporator turns a three-hour cycle into a five-hour one, or into a cycle that never quite finishes.
Detailed Analysis
What a normal cycle actually looks like
Realistic figures for a modern 8–9kg heat pump dryer, starting with laundry spun at 1400rpm:
| Load | Typical cycle time |
|---|---|
| Full cotton load, cupboard dry | 2 hr 30 – 3 hr 30 |
| Full load of towels | 3 hr – 4 hr |
| Half load of cottons | 1 hr 30 – 2 hr 15 |
| Synthetics / easy care | 1 hr – 1 hr 45 |
| Shirts or delicates | 45 min – 1 hr 15 |
| Eco or energy-saving programme | Add 30–60 min to the above |
Towels are the worst case and always will be. They're thick, absorbent and heavy when wet, and four hours for a full drum is not a fault. If your machine lands inside these ranges, it's working properly, however unwelcome that is.
The filter nearly nobody knows about
Every heat pump dryer has at least two filters. The one in the door opening is obvious and most people clean it. The second sits behind a flap or kickplate at the bottom front of the machine, catching the fine lint that gets past the first before it reaches the heat exchanger.
This lower filter is usually a foam sponge or fine mesh in a plastic frame. It needs pulling out, rinsing under a tap, squeezing dry and — importantly — drying fully before it goes back. Manufacturers say every 10 to 20 cycles; realistically every month or two is fine, more often with pets or a lot of towelling.
If you've had the machine two years and never opened that flap, open it now. The amount of compacted grey felt that comes out of a neglected one is startling, and clearing it very often restores the cycle time on its own.
The evaporator fins behind the filter
Behind that lower filter sits the evaporator — a block of closely spaced aluminium fins, rather like a small car radiator. Air has to pass through it to be dried, and fine lint that escapes both filters settles on those fins and mats down over the years. Machines with a "self-cleaning condenser" periodically flush water across them, which helps but doesn't eliminate the problem.
Inspect them once a year with a torch through the filter opening: clean fins look like combed metal, blocked fins look furry and grey. Cleaning is a careful job, because the fins bend at the slightest pressure and a bent fin blocks airflow permanently. Use a soft brush and a vacuum nozzle held slightly back — never a screwdriver, a stiff brush, or pressurised water unless the manual permits it.
Room temperature makes a real difference
This is where a lot of otherwise healthy machines look faulty in winter. A heat pump dryer works by moving heat around, and it needs a reasonable ambient temperature to do that efficiently. Manufacturers typically specify an operating range of around 5°C to 35°C, with performance optimised in the high teens to low twenties.
Put one in an unheated garage or an outbuilding and January cycle times can extend by an hour or more compared with the same load in a warm kitchen. It isn't a fault and no engineer will find anything wrong. Equally, a dryer in a small sealed room gradually warms that room and eventually struggles for the same reason in reverse — it needs somewhere to dump waste heat. A cracked window makes a measurable difference in a cupboard installation.
Sensor drying and why it stops early or runs long
Most heat pump dryers dry to a moisture level rather than a timer, using conductivity sensors — metal strips inside the drum — to judge how wet the load is. Those get coated in fabric softener residue and limescale, and a coated sensor misreads the load in either direction.
If your machine finishes early with damp clothes, or runs on after the laundry feels dry, wipe the sensor strips with white vinegar on a cloth, then a clean damp cloth. Using less softener stops it recurring.
Three habits that stretch every cycle
Spin speed is the big one: clothes leaving the washer at 800rpm carry far more water than the same load at 1400rpm, worth 20 to 30 minutes of drying. Spinning is dramatically cheaper than drying. Overloading is next — a drum crammed full doesn't tumble, and clothes that don't tumble don't present new surfaces to the airflow, so fill no more than three-quarters. And mixed fabrics: put jeans in with t-shirts and the sensor runs until the jeans are dry, by which point everything else has tumbled needlessly for forty minutes.
Real-World Considerations
It's worth putting the time cost against the money. A heat pump dryer using around 1.5–2kWh for a full cotton load costs roughly 40–50p per cycle at typical UK rates. A condenser dryer doing the same load in half the time will use 3.5–4.5kWh — closer to £1 or more. For a household drying five loads a week, that's a difference of around £150 a year.
So the slower cycle is buying you something real. The adjustment most people make is to change when they use the machine rather than how — starting a load before work rather than expecting it back in an hour. Households on an off-peak tariff benefit further, since a long overnight cycle sits neatly inside the cheap window.
Noise isn't usually an issue: heat pump dryers run around 62–65dB, quieter than most condenser models, though the compressor adds a low hum some people notice at night. One irritation worth knowing before you buy is that gentle, prolonged drying leaves fabrics slightly more creased than a hot, fast cycle would. Taking the load out promptly helps more than any anti-crease setting.
Common Mistakes Buyers Make
Only ever cleaning the door filter. The lower filter is the one that causes long cycles, and it's the one people miss for years.
Refitting a wet sponge filter. It restricts airflow immediately and encourages mould. Let it dry overnight.
Putting the dryer in an unheated garage and expecting summer performance in February. Check the manual's minimum operating temperature — many warranties exclude use outside the stated range.
Assuming a long cycle means a broken compressor. Compressor failure is rare, and the symptom is usually no heat at all rather than slow drying. Clean the filters before assuming the worst.
Alternatives Worth Considering
If cycle time genuinely matters more than running cost — a large family, laundry that has to turn round quickly — a modern condenser dryer will do the same load in roughly half the time. You'll pay for it in electricity, and A+++ efficiency isn't available in that format, but there's no point owning an appliance whose defining characteristic doesn't suit your routine.
Some manufacturers now offer heat pump dryers with a boosted or hybrid rapid programme, adding a supplementary element to shorten the cycle at the cost of some efficiency. If you like the running costs but occasionally need something dry in ninety minutes, that's the compromise to shop for.
Most households end up with a dryer for towels and bedding and an airer for everything else, which is a perfectly reasonable way to run a house.
Frequently Asked Questions
How long should a heat pump dryer take?
Two and a half to three and a half hours for a full cotton load, three to four for towels, and around an hour to ninety minutes for synthetics. Eco programmes add another half hour or more.
Why are heat pump dryers so slow?
They dry at 50–60°C rather than 70–80°C. Cooler air holds less moisture per pass, so more passes are needed. That lower temperature is also why they use around half the electricity and are gentler on fabrics.
Does a blocked filter really slow drying that much?
Yes — it's the most common cause of a cycle that's crept from three hours to five. Heat pump dryers depend entirely on unrestricted airflow across the evaporator, so lint has a disproportionate effect. A blocked filter can also trigger a safety cut-out, leaving clothes damp at the end.
Final Thoughts
Most heat pump dryers that seem too slow are simply doing what they were designed to do, and the disappointment comes from a retailer selling the efficiency figure without mentioning the clock. Three hours for a full load is normal. Four for towels is normal.
What isn't normal is a machine that has got slower over time. That's nearly always lint, and nearly always the filter behind the kickplate the manual mentions once on page 34. Clean it, check the evaporator fins with a torch, wipe the moisture sensors, and give the machine somewhere reasonably warm to live. Do those four things and it will hold its performance for a decade — at half the running cost of what it replaced.
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