Heat pump tumble dryers do not require an external venting hose, but should be used in a ventilated room. These dryers remove moisture from clothes and store the extracted water vapour onboard a tank, which is then removed and emptied down any sink, toilet, or drain when full.
Vented-type tumble dryers – as the name suggests – do not have a water storage tank, and instead have a ducting hose that must be attached to an external vent, or placed near an open window or outside door.
Heat pump tumble dryers operate the same way as a condenser tumble dryer, by condensing heat into water, and then storing this condensed water inside a water tank. Heat pump dryers get rid of water by either filling an onboard water tank or draining the water away through a small drain pile that can be attached to any wastewater pile, but they do not require any external venting.
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Heat Pump Dryer Installation and Airflow
Although heat pump dryers do not need an external vent, they do need to be used in a ventilated room. This is because of two things; airflow and condensation efficiency.
Airflow
Most tumble dryers, whether heat pump, condenser, or vented, will have an air inlet vent on the front or rear of the dryer, near the bottom. This vented kick-plate is where the tumble dryer pulls in ambient air, which is then blown through the dryer to dry clothes.
Heat pump tumble dryers have this air inlet vent which needs to be kept clear so that fresh are can efficiently be extracted from the room. The difference between heat pump dryers compared to other types is that it recirculates the air in an enclosed system, not requiring an exhaust vent.
This makes these tumble dryers suitable for use in small laundry rooms, apartments, under worktops, in cupboards (operated with door open), and enclosed spaces – provided the air inlet is clear and there is at least a 1.4cm gap between the body of the dryer and any surfaces, taking special care to ensure air can flow freely around the base of the dryer.
So when installing a heat pump tumble dryer, any air inlets or outlets should be kept clear of obstruction to provide air exchange. Otherwise, the dryer won’t be able to dry properly and could overheat.
Condensation Efficiency
The first reason that you need a ventilated room is so that the heat pump dryer has fresh air to draw in and an operating temperature of between 5°C and 35°C – around 19°C being about optimal.
The second reason – and more importantly – is to prevent condensation and a build-up of moisture in the room, which could lead to black mould and other damage to your home interior.
Although heat pump tumble dryers remove air from wet laundry through evaporation and condensation and store this condensed water in a tank, the machine can’t retain 100% of the water removed from clothes. Heat pump dryers, like condenser dryers, will “leak” some moist air during the drying process.
Some dryers are more efficient than others at retaining moist air and are given a grade between A and G. A premium heat pump tumble dryer with an A grade should retain more than 90% of the damp air inside the system with less than 10% being blown into the room.
Because even the best heat pump tumble dryers with an A condensation efficiency grade will still leak some damp air into the room – even as little as 5%, the room you’re drying in will need some ventilation.
You can find the condensation official class on the energy label, where you’ll also find the noise level of the dryer. If you’re heat pump dryer will be used in a place with decent ventilation, then you don’t need to worry too much about this grade – energy efficacy is the important one.
However, if the room you plan to instal your heat pump dryer has limited ventilation, then you should consider buying one with an A to C conditioning rating, with A and B machines being the best option to minimise condensation.
The more ventilation the better, as this means more of the moist air can escape, but you don’t need a vented extractor fan, a wide open external door or a window. A window or door slightly ajar, or a small wall vent would be enough to allow the moist air to be expelled.
So there you have it – heat pump dryers do not need a hose vented outside, but they do need to be used in a room with some fresh air and ventilation.
