forced draft or no forced draft

[micah78]

I'm considering many different forced air furnaces for heating my home with wood. I've been told that a forced draft furnace will use more wood than one with a manual draft. That makes sense to me but it's not my main concern. What I'm thinking is, won't a manual draft furnace continue to get hotter when the thermostat upstairs kicks off the blower that circulates the heat through the ductwork? When the blower is off then I would think the heat would build up unless I run downstairs and manually cut off the air thats feeding the fire. The reason I'm concerned about this is because I don't have alot of head room in my basement and my main trunk that feeds my registers is basically mounted to the floor joists. I'm concerned about the main trunk getting too hot above the furnace when the circulating blower is not on. My thinking is that a forced draft furnace should only get hot when the house needs heat and the circulating blower is on. Then when the house reaches the temp on the thermostat upstairs The forced draft blower should kick off and the fire would cool down. Is my thinking correct? or am I missing somthing?
Thanx in advance for your replys!! Micah

 

[Duetech]

Will the draft shut off comepletely when the draft fan is off or is there (presumably) a continous air flow in your stove anyway? A heated chimney will induce a certain amount of draft. I had a draft problem with a wood furnace that only mechanically induced draft would consistantly overcome. Yes it did burn more wood but like you that was not the primary issue. The furnace was built with a natural draft design and when running would overheat the house in milder weather. Cold is not the only problem as wind can raise havoc but the lack of wind can also cause a heat build up even in cold weather. Especially when a number of the family is over. The only cure was to manually adjust the speed of the inducer which was much the same as controlling the draft on the front of the furnace.

If you control the mechanical draft so it does not work unless the house is calling for heat you may find a time of call and time of delivery lapse because the fire has cooled too much. When the call for heat is over there will be a thermal build up. It was never critical with my set up and I have a low ceilinged basement and ductwork that sounds as though it is supported in similar fashion to yours. Not all situations are the same and what worked for me may have no bearing for your situation. I monitored my system persistently for the first year.

Will the wood furnace hot air vent directly in to your current system? Gravity will help reduce the trunkline temperatures during idle times even though the trunkline may seem hot to the touch. Older furnaces used to dump 140*f temps into the rooms they were intended to heat. Insert an oven type meat probe into your trunkline and see what the current operationg temperatures are. It may surprise you. You may need a back draft damper built inot your main trunk line to prevent hot air from blowing into cold air return ducting. There are a lot of considerations when putting in a parallel heating system.

 

[micah78]

I guess the reason I'm so concerned with the heat buildup when the circulating blower is not on is because I'm thinking about how hot my wood stove in my barn gets. The barn has little insulation and high ceilings so it doesn't really matter how hot the stove gets. In my basement with the wood furnace sitting directly below the trunkline and the trunkline mounted to the floor joists above, I want to make sure I don't purchase the wrong type/size furnace. As far as my house getting too hot, I'll just open some windows like others have said. I think it would be nice to be able to air my house out when its cold and not have to picture the $$$$ flying out the window!

 

[john26]

I believe most furnace circulating blowers (blows into duct work) stay on all the time even if thermostat upstairs is satisfied. There is a low limit and hi limit switch on the furnace the turns the circulating blower on and off its adjistable. If tou look in the ownwer manuals some manufactures recomend shutting the furnace down in power outages, also they want the duct work droped down 6" or so for the first couple of feet.