In an ideal world, perhaps the most efficient and certainly the most environmentally friendly method of drying laundry is to hang it on an outdoor clothes line. The vagaries of the British weather, however, mean that this is impossible to do - at least with any degree of certainty for large parts of the year and many people thus find that a tumble dryer is a convenient alternative. A tumble dryer allows you to transfer clean, wet laundry straight from your washing machine, removing the need to adorn your home with an indoor clothes line or clothes horse, or to fill every inch of available radiator space with your "smalls". A tumble dryer also reduces drying times between 70 and 90 minutes is typical for a standard 5kg load of cottons, depending on the spin speed of your washing machine and the amount of ironing required.
The first things that you need to consider when choosing a tumble dryer are how much space you have to physically accommodate one and how much drying you actually need to do. Most full-sized tumble dryers have standard dimensions of H850mm xW600mm x D600mm although these may vary slightly from manufacturer to manufacturer and a drying capacity of around 6kg. So-called compact tumble dryers, on the other hand, are smaller in all three dimensions, typically at around H670mm x W490mm x D480mm and have drying capacities around the 3kg mark. This type of tumble dryer can be useful if you have insufficient space for a full-sized machine or simply require only a small load capacity. The larger the capacity of a tumble dryer, obviously, the more the items or the larger the items such as towels, duvets, etc. that can be accommodated. Do bear in mind, however, that overfilling a tumble dryer may result in a reduction in its efficiency and increase the degree of creasing caused by the drying process.
You also need to consider whether you want a vented or condenser tumble dryer. A vented tumble dryer is the more traditional of the two competing designs. It features an exhaust hosepipe which is connected permanently to a vent in an outside wall or simply hung out of a window when the tumble dryer is operating. This handles the removal of hot, damp air from the interior of the machine. The hose itself needs to be kept free of kinks and should, ideally, be no longer than two or three metres in length. This type of tumble dryer therefore needs to be positioned in fairly close proximity to an outside wall or window. The positioning of the vent outlet in the tumble dryer itself may be important from the point of view of convenience and a choice of front, back, left and right sometimes multiple choices for the vent outlet(s) may be available, depending on the model chosen.
Vented tumble dryers tend to be less expensive and more energy efficient than the more recent, "condenser" tumble dryer design. Condenser tumble dryers collect moisture by means of -- you've guessed it -- a "condenser" effectively a radiator supplied with a stream of cold water and a reservoir, rather than venting steam so no external hose is required. This means that a condenser tumble dryer can be positioned anywhere is the home but the reservoir does need to be emptied regularly typically after every drying load and the condenser apparatus and filter also require regular cleaning to maintain maximum efficiency.
Energy consumption and efficiency is important and there is no discernible difference between vented and condenser tumble dryers in terms of either. In fact, a gas tumble dryer which uses gas to heat the air which dries the clothes but still uses electricity to turn the drum is the most economical and efficient of all. Gas tumble dryers are, however, very few and far between and the apparent savings in energy consumption must be offset against reliability which is on the whole, less than that of electric dryers.
Generally speaking, the EU Energy Label can provide much, if not all, of the information that you require regarding the energy efficiency and performance of a tumble dryer and can be a useful method of comparing one model with another. Every tumble dryer is assigned a rating from "A" (the most energy efficient) to "G" (the least) for energy efficiency and while A rated tumble dryers are likely to be the most expensive initially, they are equally likely to have lower running costs. The EU Energy Label also lists the amount of energy required in kWh or "kilowatt hours" required for a typical drying cycle.
So-called "sensor" tumble dryers which have an electronic sensor that detects the amount of moisture remaining in a drying load and adjusts the drying time accordingly are more efficient in terms of energy than "timer" models. Timer tumble dryers, in turn, leave the choice of drying time entirely in the hands of the user by allowing a specific drying time or type of drying "iron dry", "cupboard dry", "extra dry", etc. to be selected manually. Timer models are the less expensive of the two types but do require some knowledge on the part of the user with regard to drying times for specific load and fabric, types and introduce the possibility of over drying clothes so that they become stiff. This danger is lessened by a sensor tumble dryer which is also very straightforward to use, although accurate drying times are dependant on the quality of the sensor. Less expensive sensors tend, on the whole, to be less accurate. A sensor may also be less accurate if you attempt to dry fabrics of different weights and densities in the same load, so it is a good idea to always dry like with like.
Many tumble dryers also offer at least two heat settings and specialised drying programmes, for example, for drying wool or other delicate fabrics at relatively low temperature and with only gentle rotation of the tumble dryer drum. Many also employ a "cool tumble" cycle at the end of the drying cycle proper to cool items down sufficiently that they can be comfortably handled.