Health row customs

Which terminal are you arriving at? Currently all flights departing to Dublin (BA or Aer Lingus) go from T1, but where you are arriving at will determine connection times. Also are you are on a single ticket?

Jane - Which airline will you be using to fly into Heathrow?. I did this a few years ago flying BA. I had a 4 hour layover and thought this was more than enough time to get from T5 - T1. I almost missed my fight.

Haven't made purchases. Just looking at options. Leaving from Dulles will have to go thru Heathrow. Leaving from Philadelphia can go to Dublin thru Toronto which sound less difficult and only about $100 difference. Entire itinerary is Philadelphia (?) to Dublin and then Dublin to London and then back to USA.. It looks like it may be cheaper to buy the Phil to Dublin and the Heathrow to Phil as a single tix and then purchase Dublin to London on ae lingus I have found $1361 for the first ticket on united/air Canada. And $61from Dublin to Heathrow. Does this sound like a good price. Wondering if should purchase now or wait to see if fares go down. Trip is mid August and returning sept 7.

So you are actually looking at flying from Dublin to the USA via Heathrow. That makes a whole load of difference. If flying to Washington on United you don't need to change terminal as both Aer Lingus and United use T1. You will arrive into Heathrow effectively as a domestic passenger as you haven't left the Common Travel Area. If you aren't able to through check your bags you would collect them in the domestic baggage reclaim area. Just take your bags to United check-in and clear security. If you are able to through-check then it is transfer security only (follow transfer signs). If on two tickets you are on your own if the flight into London is delayed and you miss the Washington one (or at least at the mercy of United). The minimum connection time if on one ticket is 60 minutes.

I must say I hadn't considered the Terminal 1 to 5 thing; we'll have just 2 hrs 10 mins from our arrive to depart to DUB. Glad to know now!
As for fares, and we are going Los Angeles LAX to LHR then on to DUB, that fare one month ago cost us $1186, it's now $1332 for mid August. Hard to say with air fare, but I felt then like it wouldn't get any cheaper and it hasn't-although Aeroflot at the time was the cheapest, a few hundred less, but no thanks I'll stick with BA thanks very much.

Minimum connection time for T5->T1 Ireland connection is also 60 minutes - this means doing it airside rather than landside of course with bags checked through. You would have twice that time - and being on a single ticket you would be put on the next flight anyway if the incoming flight was late (either BA or EI plane as there is a codeshare).