Yes, it should be enough time if your incoming flight isn't late but if you've booked a through ticket and you do miss your connecting flight the airline is obliged to get you on the next available flight.
You will have to clear customs in Houston if you are flying in from Costa Rica and making your next flight in less that 90 minutes sounds like not enough time to me. Lots of people say allow 3 hours for that sort of transfer.
If you have carry on only you can use the One Stop facility which is unique to Houston and as far as I'm aware offers a quicker clearance.
I've done international to domestic once at Houston with checked bags, and on that day I wouldn't have made a 1hr30 connection. But YMMV, and United will look after you and rebook you on the next flight with available seats should you miss the connection.
If you have carry ons only and use OneStop you should be fine, as it has a dedicated immigration line. People were sailing through that while I was stuck in the normal line for a good 45-50 minutes.
Is a one our layover inhouston enough ? I'm flying form Belize to San Fransisco.
Post 5. Try not to have the name of your company as your username. People may think you are trying to advertise ;-)
"Is a one our layover inhouston enough ?" - In my opinion that's not long enough to clear Immigration, Customs and get to your gate.
You've bought your tickets? It's a moot point, isn't it? Make the best of what you have. Assuming both flights were ticketed together, if you somehow miss your connection, the airline taking you to Costa Rica should put you on the next flight with available seats (may not be the very next flight) should you miss your connection.
Tidetours, you should start your own thread, so it's clear to whom posts are responding, but I'd say the simple answer is almost certainly not, even with flights ticketed together. Entering the U.S. takes more time than leaving, as is often discussed on this branch.
One hour is very tight and I would not book that connection. If everyone in your party has carry on luggage only you may just make it because of the OneStop facility covered in post 3. But if anyone with checked baggage will have no chance.
We had a 56min. connection and made it fine. That was mexico to Edmonton via Houston. We also had 3 little kids with us. We had checked luggage and used the one stop.