You stay at the terminal linked by an indoor bridge. This is first & foremost a lovely hotel which, secondly, is conveniently located for travel from Heathrow...instead of the other way round. You get away from all that is pre-travel and relax with the services fo a very good restaurant, a lounge bar and a harmonious tea & coffee lounge to name but a few of the facilities. As well as being a great stay I also use the hotel for those extra meetings I squeeze into the beginning or end of my business travel itineray to the UK. It's the perfect place for these.
Also. remeber that the Heathrow Express operates free for inter-terminal transfers so even if you're leaving/arriving form another terminal, you can access this hotel from the lift at the HE train station under terminal 5.

I used this hotel for a quick overnight from one flight to another the next morning. As a member of Accor’s A-Club program it was ideal for that purpose, especially given that it is located at LHR terminal 5, where I was departing the next day. The hotel is very modern & spacious, well presented & equipped, but it is after all a ‘bed factory’. Its very, very busy, with moderate staff attention [simply I suppose because of the volume of customers it processes every day]. It’s a typical high-volume, less than personal hotel. Its almost a captured audience. I had no issues, the staff were friendly, the room was great. Its really only ideal for an overnight. The hotels’ normal room rates are the most expensive at LHR & it regularly rates as LHR’s number one hotel. I stayed here because I was able to secure a very attractive [weekend night] rate. Had it not been for that, I would have stayed elsewhere and paid the [what is it] 5GBP for the Hopa bus to a less expensive property. Very nice property, but excessively overpriced and sadly lacking in personal attention.