harmon SF-3500-A

a friend of mine has a harmon sf-3500-A , hot air furnace in his cellar he claimes its not burning hot enough he doesnt burn coal in it he burns wood in it. it has a auto matic draft does he need to have a barometric damper and he says the blower isnt big enough , i told him the blower is a 1400 cfm blower. written in the features it says it has a 3 speed blower switch and then in the written specifications it says number of blower speeds one. can some one help thanx.

He should check his stovepipe temperature, could be his heat is going up the chimney instead of into the ductwork. If he has a real good chimney and no barometric damper that is what will happen. That thing is rated 170,000 BTUs with wood, so he should have plenty of heat. My boiler has a single speed blower and the only trouble with wood is you have to load it every 4-6 hours or your done, it makes plenty of heat.

the heat isnt a prob, misunderstanding on my behalf. not enough pressure in his duct work the main part of the house has good blower pressure to push the heat into the rooms its the addition of his house that is needing the pressure in the upstairs bedroom and his bedroom . by the time the heat comes into that side of the house there isnt enough blower power to push the heat into the rooms from out of the heaters. any suggestions? thanx

Balancing the air delivery in ductwork is something that is supposed to happen when the ductwork is first installed in the house. With an addition, often the main ductwork is just added to, rather than increased in capacity to handle the new heat requirements. This results in several poorly heated rooms.

Moving hot air is both pushing the air in the ducts, but also the return of cold air to the furnace for reheating. The cold air returns are often ignored or very inadequate. Both sides of this loop are important.

If you can, find out the number of rooms, how big they are, the size of the ducts and where the heat duct outlets are located, and where the cold air returns are located.

Often, there will be hot air outlets in each room, but only a central cold air return in a hall way. When the bedroom doors are closed for privacy, there is nowhere for the hot air to go once it is in the bedroom, it can't get out to the cold air return. The room becomes a 'balloon' and can't be inflated anymore. If the door is left open the room will have lots of heat in, and cool air out and be comfortable.

So there is no single answer to the airflow problem. There are in-duct fans that can be added to increase flow, but both sides of the air-loop must be attended to. Often new larger ducts must be built into the house to truely 'fix' it.

One simple way is to just close off the heat outlets to the living room, family room, and other unused rooms at night, then open them again when in use. A bit agravating, but this is a built in limitation with hot air systems: no separate heat zones in most systems.

Hope some of the above helps. Greg L.

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what is the three speed blower switch? maybe its set to number one instead of number 3 lets just say. and is there a question of putting a bigger blower on the unit? and also should he put a barometric damper into the pipe thats tied into his chimney he curently does not have one. he installed the harmon himself and no one told him about the baro and he acted like i was from planet zoom when i mentioned it. any input would be greatly appreciated.

bigchunk wrote:what is the three speed blower switch? maybe its set to number one instead of number 3 lets just say. and is there a question of putting a bigger blower on the unit? and also should he put a barometric damper into the pipe thats tied into his chimney he curently does not have one. he installed the harmon himself and no one told him about the baro and he acted like i was from planet zoom when i mentioned it. any input would be greatly appreciated.

A three speed would have 3 different RPM settings for the blower speed.
If it is a belt drive blower, it could have three different size pulleys on the motor and blower shaft and you could adjust the blower speed that way. That could possibly solve the air flow problem.
If the pulleys have different ODs, would switching them increase the fan speed? The big one on the motor will spin it faster.
The blower on the furnace may need to run at a different speed or is not sized properly. Keep in mind that if you are losing heat up the chimney, you will have more trouble keeping your plenum hot enough.

Review the baro stuff here; http://www.fieldcontrols.com/draftcontrol.php#draftwork
Anthracite pretty much requires a barometric damper, but wood units rarely mention baros and I'm not sure why. If he burns coal he definitely should have one. Get a draft gauge and use it no matter what you burn.

If I had a hot air furnace I would want a thermometer in the plenum and one in the stovepipe prior to the baro. The more info you have the better you can tune it. (actually, the more gauges and meters you can hook up to the monster, the more you scare the uninformed )

does anyone here have a furnace like the sf- 3500-a or anything similar what settings do you have on your stove. can someone tell me about there exsperience with burning coal in theres. especialy with that auto matic draft system did you need to make a adjustment with that "screw on there " and how much of a adjustment did you make.