Imagine Furnace Overheated in 20 deg Weather

[Steve&Camy]

We own a 2017 2500RL manufactured in Nov 2016, serial 404519.

PROBLEM
We camped in NW Iowa for one week with most overnight temperatures around 35 degrees. On Oct 30th, when the outside temp was 20 deg, our furnace quit...we woke up with 58 deg in cabin (thermostat was set on 68 deg) and noticed furnace was off.

INVESTIGATION
After checking the thermostat, the furnace, and the furnace installation manual I concluded the "limit" switch may have tripped due to high heat behind kitchen cabinets where the furnace and water heater are located. I removed both drawers under the kitchen sink, turned furnace off for 5 minutes, then on, and it ran fine the rest of the night. It also ran ok the next 5 nights as well with drawers re-installed, however the overnight temp never got below 30 deg again in those 5 days.

POSSIBLE CAUSE
After reading the furnace installation instructions I determined that the installation in our 2500RL does NOT meet the minimum duct area of 48 sq-in (to be calculated by "ignoring area of all 2" dia ducts"). Also, it does not meet the minimum cold air return area. Reduced air flow through the furnace could cause over-heating if the furnace runs a long time (i.e. in 20 deg outside weather).

INTERIM SOLUTION
I plan to leave kitchen cabinet drawers and/or doors open during cold nights. I also reduced the height the floor-mounted plywood panel (toe-kick panel) under the drawer (located beneath the oven) in order to increase the area for cold air return.

BETTER SOLUTION
It would be helpful to add another 4" dia heat duct, but I do not see any good place to run it to. The furnace currently has three 4" dia ducts to cabin and one 2" dia duct to heat the belly. The furnace distributes heat well...with both bathroom doors closed at night, the bedroom is a little cooler than living area, and bath is a little cooler than bedroom.

QUESTIONS
Are there any easier solutions?
The furnace seems to have plenty of capacity for 20 deg outside weather (it was also very windy that night), can orifice be changed to reduce the Btu/hr heat rating?

Regards,
Stephen

[GDRV Missy]

Good Afternoon,

I forwarded your concern to a regional service manager here at Grand Design. He replied: "There is really no easier solution than running another duct, on that unit there is no good place to add a vent for cold air return."

Thank you,

Missy