One in five households are behind on their electricity bill, according to a new survey for the Energy Regulator.
A further 14% manage their bills by paying in instalments.
Gas customers fare slightly better - 4% of gas customers said they are in arrears, and a further 16% make partial payments.
One in eight of those polled say they switched suppliers last year.
10% of electricity and 18% of gas customers say they would consider switching. 10% said they are interested in equalised billing, where payments are spread evenly all year round.
The study found there has been a surge in customer interest in prepaid options like meters to avoid heavy bills.
It also found that most consumers are unsure about how energy prices are structured or understand rival plans from different suppliers.
The survey of 1,000 electricity and 1,000 gas customers was carried out by Behaviour & Attitudes for the Energy Regulator.
Dermot Jewell of the Consumer Association of Ireland said the energy regulator should do more to provide clarity on how the pricing systems work, so that people can switch providers.
"We've been through a nasty recession. We need the ability to know how and when to change," he said.