HR20 HD DVR is extremely hot

II recently  upgraded from standard service to HD and purchased a HD DVR as well. The installer brought an older reconditioned HD20 DVR. He told me that these units produce a lot of heat and he was absolutely right. This thing is barely cool enough to touch. I have it in a cabinet, but the door remains open and there is 4-5 inches clearance on top and several inches on each side and probably 10 inches in the rear. It is so hot, it is heating up the shelf on top of it that is 4-5 inches away. I know that heat is the enemy of electronics and am concerned about a shortened service life of this unit due to this. Any historical data on the heat these things produce? I was disappointed in the first place that as a 5+ year DirecTV customer I was offered much less than a new unknown customer and then the installer brought a reconditioned older model that I paid $99 for. Appreciate any info on the heat issue. Please don't tell me to move it as there is plenty of clearance already around it.