Hi Robert, Just a update here. The HVAC tech was here a week ago. Gave me thumbs up on my cleaning job and measured 0 ppm on the CO2. The tech agreed with you that closing the manual fresh air door at the furnace is no problem. Apparently the latent heat build up on these older (1985) Intertherm gas...

Bmerri, I found the same situation when I bought my 1985 single wide a few months ago. Amazing to think that for all those years the owners thought that was OK to vent underneath the home! Yeah, there was lots of lint down there, of course. Now it's properly vented to the outside just as flcruising ...

Thanks Robert, have a HVAC tech coming by Friday morning. There's so many potential problems I need a trained set of eyes. This furnace is so old (1985) it has a manual door for outside fresh air. Been keeping it open but is there any time that it should be closed?

Thanks,
Jeff

I have an Intertherm MGH-055AB furnace in my mobile home. The heat cycle seems normal now that I replaced the fan limit control. One thing, about 5 minutes after the cycle the fan comes back on for about 30 seconds to remove latent heat, I assume. Is this normal?