There are several options to go from Heathrow airport to Torquay.
If you decide to go by bus, there are 9 daily buses and in about five hours you are at the destination.
By train, the duration of the trip is a little longer, since there is no direct train, but there is more frequency of trains. One every half hour.
But the fastest and most expensive way is also to do it by taxi, since it only takes about 3 and a half hours