there was a discussion i think last year about heating an old drafty house almost exclusively with an nc-30. i have an approximate situation and right now it is 12 degrees outside, wind howling. last night it was 8. inside it is 73 downstairs and 70 upstairs. i remember a lot of back and forth about the inability to do the job. unless its -30 or -20, it will definitely do the job. also, my install is on an old porch addition facing into the house, not a center house install.