CNBC: Health Savings Accounts Are the Big Winner as Republicans Hash Out an Obamacare Replacement

HSAs have grown to an estimated $37 billion in assets and 20 million accounts at the end of last year and reached $41 billion in assets during January, according to Devenir, an HSA consulting firm in Minneapolis.

Given the momentum, Devenir forecasts assets in the accounts could reach more than $53 billion by 2018, a 20 percent increase from this year.

Devenir estimates that about 10 percent of the roughly 20 million HSA account holders have a balance of $5,000 or more and 4 percent of people are using their HSAs as investment plans. Many HSA providers require that you have at least $1,000 in your account before you can invest.

How should people invest their HSA money? Generally, you should have enough cash in your HSA to cover expected medical expenses and invest the rest.

HSAs can travel with you if you change jobs or insurers. Use HSASearch, which is run by Devenir, to comparison shop for more than 320 providers. Just like with any retirement account, fees and investment options matter.