Tube from Heathrow to Bloomsbury in London?

there are No Express Trains on the Tube
Crowded depends on what time of day- it will be crowded during Normal commuter hours

expend 45 minutes at least

https://tfl.gov.uk/plan-a-journey/

Not express or local..Is a TUBE....about 50 mins...RUSSELL SQUARE...Stops at each station..Can get busy during peak times...WATCH bags.

Around an hour. There is no such thing as an express tube. Whether it's crowded depends on when you arrive, but Heathrow is at the end of the line so you will be one of the first on. If the first train looks full, wait for the next and get on it first to grab a seat!

LadyMerton says 45 mins. No. I think more like an hour. The Tube is usually very crowded at Heathrow because of all the tourists with loads of luggage, but it thins out by the time you get near the centre.

The express train from Heathrow goes to Paddington Station and not direct to Russell Square as the Underground Piccadilly Line does. If you have heavy luggage or dislike crowds take the Express to Paddington and then a cab to your hotel
www.heathrowexpress.com