It is blowing warm air

Where the warmth comes from

Two separate sources, and both are unavoidable rather than a design compromise.

1. 1The electricity. Everything the machine draws - compressor, fan, controls - ends up as heat somewhere. In an air conditioner that heat goes outside through the second coil. A dehumidifier has no outdoor half, so all of it stays in the room. For a 50-pint unit that is about 488 W, which is a small space heater.
2. 2The water. Condensing water vapor releases the energy it absorbed when it evaporated in the first place. That heat is handed to the coil and blown back into the room along with everything else. It is the same latent heat that makes a humid day feel heavier than a dry one at the same temperature.

So the air leaving the machine is warmer and much drier than the air going in. The full mechanism.

How much warmer, in practice

Enough to notice at the outlet, and usually not enough to change the room much. The exhaust stream feels distinctly warm on your hand because it is a small volume of air carrying the machine's whole heat output. Spread across a basement it is a couple of degrees at most, and in a cool below-grade room that is generally welcome.

We are not going to give you a temperature rise figure for your room, because it depends on the room's volume, its insulation, how much air leaks in and out, and what else is running. Anyone quoting a single number for that has invented it.

When the warmth is actually a problem

• In a room you are air-conditioning. The air conditioner now has to remove the dehumidifier's heat as well as everything else, so running both hard in the same room costs more than either alone. Set the thermostat a few degrees higher to claw some of it back - drier air feels cooler at the same temperature. The full comparison.
• In a small enclosed space in summer. A closet or a small store with a compressor unit in it will get noticeably warm, because there is very little air to spread the heat into.
• With a desiccant unit, much more so. A desiccant machine uses a heater to drive moisture out of its rotor, so warm exhaust is not a by-product there - it is the mechanism. That is an advantage in a cold garage and a real nuisance in a warm basement. Desiccant versus compressor.

The one case that is genuinely wrong

Warm air and no water. If the exhaust is warm but the bucket stays empty and the room's humidity does not move, the fan and the controls may be running while the refrigeration side is not doing its job. The warmth you are feeling is then just the fan motor and the electronics rather than a working cycle.

Before assuming that, rule out the ordinary explanations in order - a room cooler than about 60F, a humidity target already satisfied, a drain cap still fitted, a clogged filter. Those account for most cases. The full checklist.

What you can do about it

• Nothing, if the room is cool. In a basement the added heat is neutral or mildly useful, and it is the price of the water removal you wanted.
• Move it away from where you sit. The exhaust stream is what you feel, not the room average.
• Do not point it at a wall or into a corner. That is bad for airflow generally, and a starved coil ices. Icing up.
• Run it on a humidistat rather than continuously. A correctly sized machine reaches its target and idles, and an idling machine adds much less heat than one running flat out. Ideal humidity settings.
• If the heat is genuinely the problem, the machine may be the wrong tool. A room that is both hot and humid is an air-conditioning job first.