The Heathrow Freeflow Zone is an area within the immediate LHR airport area that provides free bus service (sponsored by BAA). I am writing this as much as a reminder to myself as information that many may find very useful. As every time I am staying at a hotel near Heathrow I forget where I put this information. I have been taking advantage of this program for the last 15 years or so.
If you are staying in a hotel along Bath Road (Park Inn, Holiday Inn Heathrow, Renaissance Heathrow, Radisson Edwardian, Sheraton Skyline, or Marriott Heathrow), you can take the following buses from the Central Bus Station at LHR Terminal 1,2,3 ; 105, 111, 140, 285, 423, 555, & N9 to these hotels. As long as you are only traveling within the Freeflow zone (see links below for exact area) there is no charge for these local buses. As a warning, they do not drop you off at the hotels, but at bus stops along Bath Rd. Some stops are a few yards from the hotel while others may be a few hundred yards. So if you have a lot of luggage or want door to door service, than it may be better paying the 4 Pounds (each way) for the Hotel Hoppa (bus service from each terminal at LHR to area hotels). But if you have a small amount of luggage or do not mind a short walk, than this service can save you 8 Pounds per person (Children are free). Or if you are staying in one of these hotels and want to take The Tube into London this is also a great use for this service (you can access Hatton Cross with Bus # 111 & 285 as well). I have used these buses while staying at The Renaissance, Marriott, and both Sheraton’s, but since I usually stay at the Heathrow Hilton (Terminal 4) I have mostly used this service to have dinner at a very good Italian Restaurant (IL Basilico) just off Bath Rd. (there is also a pub that serves food and a McDonald’s on Bath Rd). From Terminal 4 just take the Heathrow Express (free service) to Terminals 1 & 3. Follow the signs to The Central Bus Station and look for one of the buses I mentioned above. Just let the driver know you are going to Bath Rd.
There is additional Free Bus service to other hotels in the area (consult link below) and from Terminals 4 & 5 (it may be possible to take a bus directly from Terminal 4 or 5 to Bath Rd. and not have to take the Heathrow Express to Terminal 1 & 3). I have also used this service to travel from Terminal 4 to the Central Bus Station because I had a very early morning flight out of Terminal 1 and the Heathrow Express did not start service early enough. I know there are buses that go the other direction on Bath Rd. that have stops near the Arora International, Thistle Heathrow, and the Sheraton Heathrow.
Below are 2 links with more information on The Heathrow Freeflow Zone.