Suburban forced air furnace

[Red_Eye]

I'm looking for advice or others experiences with a suburban forced air furnace. My fish house is 6 1/2 x 14 with spray foam insulation all around. My furnace cycles as follows. Thermostat start furnace, furnace fan goes into a purge for about 10-15 second, gas valve open and ignites flame. Furnace runs for awhile and puts out heat. I'd say the temperature of the fresh air leaving the furnace and entering the fish house is around 125 +/-. Then after a few minutes the gas valve cycles off even though the thermostat has not reached it set temperture. Fan continues to run and much cooler air enters the fish house. Then after a few minutes the gas valve and igniter cycles again and I get warm air again. This continues cycling hot and cool until finally the temperature is high enough to trip the thermostat (or not) and then it goes into a cool down sort of a reverse purge. My fish house is insulated enough that I can run my Big Buddy heater on low and get the temperature up to 75 F even last Sunday at minus 7 F so its not an issue of the insulation. I've been advised to switch to 30 pound tanks. I have 20 pound tanks. I'm having a hard time with this suggestion as I'm able to have good gas flow to my oven or burners while the furnace is running and cycling as it does. I did notice the copper tubing where it enters the fish house is frosted up. Regulator problem? Any suggestions or advice is appreciated.

[walleyewiz0212]

Maybe a high limit switch is bad on the furnace. That might cause it to shut off the gas untill it cooles itself down and then kick in the flame again.

[bkiceboat]

try turning ur lp tank off and slowly turn back on with furnace off lp tanks have a excess flow valve in them if u open it too fast they pop shut....i have had this happen to my ice house with the same furnace...not real impressed with the furnace either!

[dougger222]

I ran a 30K BTU Suburban furnace in the camper turned fish house for a few years and found the unit to be a little tempermental. It seemed like the thermostat went out every year and when the battery got low it would just blow cold air. When it worked as advertised it made real good heat.

[limited out]

i agree with dougger. we've had ours a few years and love it when it works properly but have had some minor issues including the temp register.

Try looking at your regulator air vents connecting to the propane tank. Ours froze up a few years ago and restricted the heat similar to what your are experiencing. We always loosely wrap a towel around our regulator vents now to prevent freeze up.

[hovermn]

Is the furnace ducted? If so, make sure each vent is wide open. I had a suburban furnace with three ducted vents hooked up. If one of them was closed, either on purpose or accident, my furnaces would do a similar thing. It wasn't able to evacuate the hot air fast enough, and would trip the high temp limit.

If your furnace is not ducted make sure it has a free, unblocked air flow. If it's clear check your high limit switch.

[Red_Eye]

Thanks for the feedback. I think (hope) the solution is ducting. I finally found a web site that states a minimum of 3 warm air ducts for the size of my furnace SF30. It was installed with only 2 ducts. Now the challenge to figure out how to duct the third in a very limited space under a cabinet and stove. I think a SF20 would have been large enough for my house. The SF20 only requires two ducts but I've got what I've got so its time to adapt and improvise.

[crappiekid]

hover man nailed it. Make sure vents are wide open. Also try a new reg. between the two you should be all right. I installed a second heater (Empire direct vent) for back up. Suburban forced air is great for drying your floor and more efficient heating. I am a light sleeper and prefer a back up. The empire accomplishes that.

[hovermn]

I had the SF30, and loved it! The floor dried very quickly, and once it got up to temp, it ran very efficiently. I ran the furnace under the side bench with 3 ducts. One facing back, one forward, and one off the side. Talk about even heat! No cold spots in the house.

If nothing else, run 3 vents, but for 2 of them, bring them to a single house style register. That may allow you room for 3. Just an idea.

[Red_Eye]

Thanks again. Lack of sufficient air flow/2 vents versus 3 was the problem. It runs great now.