Suburban furnace question

[svonasek]

We just finished our fish house a couple of weeks and got it out on the lake. We installed a suburban nt-20-se furnace (19,000 btu. The house is 8x16 plus a 3' vee. The entire house is spray foamed atleatst 2.5 inches thick.

I'm just not happy with the results we're getting from the furnace and would like to know if what I have is just the normal for a forced air in an ice house.

The furnace will start up and run. It builds heat fairly fast coming out the vents, but the heat doesn't stay constant while the furnace is running. While heating the blower motor will stay on the entire time until you can physically see the thermostat open up. While the blower motor is running the burners will be on for about 2 minutes then shut down. Then about 30 seconds later you can hear them re-light and start heating again.

It takes over an hour to go from 20 degrees inside the house to about 60 with the furnace.

I have a 3 burner rage top also. I can take the house from 20 degrees to 60 in about 20 minutes with just the burners (no furnace).

Thanks in advance for any help

[Tom7227]

I would bet that it has something to do with the high limit switch on the furnace. Of course I am not familiar with your rig but that's where I would start checking. Owner's manual can probably help out. The high limit switch shuts down the gas when the heat exchanger gets too hot. Other issue could be the positioning of your thermostat - is it getting a strong blast of the hot air and indicating that your at temp?

[Lip_Ripper Guy]

I have the 16,000btu Suburban. With mine, the blower starts up for 15 seconds, you can hear it click, and then the burner lights. Temp stays consistent the entire time it is running, until the burner shuts off, and then the fan stays on for another minute to blow the remaining heat out of the furnace. It sounds to me like yours may not be working properly.

In my house, it could take an hour for just the furnace to bring it up to temp, but I fire up the 3 burner cooktop and it'll be warm in 15 minutes. So, that is what I do each time out.

[svonasek]

I would bet that it has something to do with the high limit switch on the furnace. Of course I am not familiar with your rig but that's where I would start checking. Owner's manual can probably help out. The high limit switch shuts down the gas when the heat exchanger gets too hot. Other issue could be the positioning of your thermostat - is it getting a strong blast of the hot air and indicating that your at temp?

[Minnie_sota_Mike]

My Attwood did the same thing once when we had a LP tank that was to full.

[svonasek]

I think I figured it out. I think the vents are restricting the flow too much and causing the high temp switch to trip out. I took the front cover of and let it run. It no longer shuts the burners off until the thermostat opens up.

Time to punch a hole and add another vent or two...

[Tom7227]

Check out the threads that talk about propane take problems. A couple of guys were writing about similar issues and it ended up being something about there not being enough surface area on the small tanks to allow the propane to go from liquid to gas fast enough when there's a large draw like a furnace. I'm not doing a good job explaining but there were good answers on those threads.

[svonasek]

I added a 3rd vent coming right of the front cover of the furnace. Everything works great now.

The manuals do say to minimize as many bends as possible in the flex hose, but I was surprised at how little restriction it took to make the thing run poorly.

[Minnie_sota_Mike]

That makes sense,Glad you got it figured out