London to Dublin-time between flights

Is this going to be on one ticket or two?

I am assuming that you are buying a seperate ticket for the connecting flight to Dublin on Aer Lingus.
Give it 3 to 4 hours in case the flight to LHR is delayed
For example if you arrive LHR at 9 am make sure the flight to Dublin leaves at Noon or thereafter.

2 tickets. There is another flight leaving an hour later, I guess that would work. The flight into Heathrow is a non stop from USA.
Is it far from Dublin Airport to downtown Dublin & how long?
Thanks for your help

Heathrow has 4 terminals. You may want to check what terminal you are landing at and what terminal the connecting flight you want to make in hour is leaving from.

Here is information on Taxi or Bus transfers options into Dublin from airport
It is 10km or 6.2 miles
https://www.dublinairport.com/to-from-the-airport/by-taxi

If you want to take the bus into town, there are two companies and three routes. All show a list of hotels near each stop. Find your hotel, and take that route.

I've taken the buses a few times and they are very convenient. Although with all of the road construction going on in Dublin they don't always stick to schedule. Give yourself extra time when going back to the airport.

When you have your flights or want to check flights, go to the Heathrow Airport Flight Connections website, plug in your flight info and it will give you step by step instructions on what you need to do as well as minimum connection times suggested.

Two hours is tight especially if you have to change terminals.

If your Aer Lingus ticket is purchased entirely separately, the airline may not allow you to transfer to a later flight if the first leg is late. That's a drawback to these short-hop and presumably cheap flights. Flying trans-Atlantic (if you are) will be more secure if you use AL or its partner airlines to buy the complete trip.

One thing not mentioned yet is that when purchasing a separate ticket as an onward flight, you take the risk if something goes wrong and you do not make your flight. You could have delays on your trans-Atlantic flight, Immigration could be packed, if you check bags you need to wait for those, timing of trains or buses between terminals can be a factor (you may have to wait 10-15 minutes) and then you will need to go through security again possibly.

Normally I do not do this, if I do, then I usually plan a wider time buffer, or just stay at the initial destination for a night. I would definitely understand what the ramifications of missing your flight is. Do you forfeit the ticket and have to buy new? Do you need to pay a change fee and the difference between ticket costs? or can you buy a higher cost ticket that allows you to change flights at no cost? Basically, have a "Plan B".

Where in the US are you flying from? Are direct flights to Dublin available instead?

Sorry for the delay in response, working on a separate trip for next month. Thanks for everyone's help.
We are flying British Airways non-stop from Phoenixe, Az to Heathrow. We then will take a flight to Dublin for a tour, then we fly back to Heathrow from Belfast and will be staying in London, then coming home. That's why i didn't get flights into Dublin. And I couldn't find an Aer Lingus flight from Phoenix. I was thrilled getting a NonStop flight out of Phoenix because that is rare. The flight arrives at Heathrow in Terminal 3, and I believe the Aer Lingus short flights are at terminal 2. We thought we would get the flight that allows 3hours between to give us time to get through customs and to the terminal.

If you haven't purchased your flight from PHX-LHR, know that not only does BA fly from London to Dublin but all of Aer Lingus flights between London and Dublin are also BA codeshares since they have the same parent company.

You could book PHX-LHR, LHR-DUB, BHD-LHR and LHR-PHX by using the "multi-city" option rather than round trip or one way on the British Airways website.

This way if there is a problem with your PHX-LHR flight being late and you miss the connection, BA will be responsible for putting you on the next available flight to Dublin.

Looking at the BA site with some dummy dating, you can also do this as Phoenix to Dublin as the first leg (rather than 2 legs), this can get you that direct flight from Phoenix to London and two hours later the Aer Lingus to Dublin on one ticket so you are protected. 2nd leg is Belfast to London, third leg is London direct to Phoenix. You can also get via BA Phoenix to Dublin by waty of Chicago ratehr than London. Aer Lingus does fly out of Terminal 2, but that is interconnected to T3 and you walk between them.