10 Best Boilers of 2020 | Gas, Propane, Oil, Electric

May 06, 2020 · The Slant/Fin Sentry boiler is a gas hot water boiler with an efficiency of 84.4% AFUE. The Sentry comes with several noteworthy features such a pre-purge option to conserve heat, a LED display which monitors system water temperature and allows the user to control the temperature as well, and a specially-designed insulated jacket to prevent heat loss and reduce operating noise.