They’re called “assumable mortgages,” and, IIRC, there were pretty popular back in the 1980s when interest rates were very high. Here’s some more info:
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An assumable mortgage allows a buyer to assume the rate, repayment period, current principal balance and other terms of the seller’s existing mortgage rather than obtain a brand-new mortgage, according to James Hines, a spokesman at Wells Fargo Home Mortgage in Des Moines, Iowa.
In theory, any type of home loan could be assumable. However, only two types of typical loans have this feature: FHA loans, insured by the Federal Housing Administration, and VA loans, guaranteed by the U.S. Department of Veterans Affairs. Conventional loans typically are not assumable.
