Energy Advisor

[Mel Cheeks]

Hi,

I would like to know some detalied information about the difference between induced draft and power vented boilers and furnaces.

Thanks

New Member

[Scott Patterson]

Hi,

I would like to know some detalied information about the difference between induced draft and power vented boilers and furnaces.

Thanks

New Member

Specifically what do you want to know?

[Mel Cheeks]

Specifically what do you want to know?

I would like to know how each one operates and specifically how to tell the difference between the two. Please exclude condensing systems form the explanation of power vented systems. I understand what I am looking at when I look at condensing systems but some induced draft, and fan assisted seem to be the same type of system. Some lead to a chimney and some are vented with stainless steal piping leading to the outside.

Thanks

Mel Cheeks

[Garry Sorrells]

A little help maybe.

Boiler - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Boiler)

Controlling draft

Most boilers now depend on mechanical draft equipment rather than natural draft. This is because natural draft is subject to outside air conditions and temperature of flue gases leaving the furnace, as well as the chimney height. All these factors make proper draft hard to attain and therefore make mechanical draft equipment much more economical.
There are three types of mechanical draft:

Induced draft: This is obtained one of three ways, the first being the "stack effect" of a heated chimney, in which the flue gas is less dense than the ambient air surrounding the boiler. The denser column of ambient air forces combustion air into and through the boiler. The second method is through use of a steam jet. The steam jet oriented in the direction of flue gas flow induces flue gasses into the stack and allows for a greater flue gas velocity increasing the overall draft in the furnace. This method was common on steam driven locomotives which could not have tall chimneys. The third method is by simply using an induced draft fan (ID fan) which removes flue gases from the furnace and forces the exhaust gas up the stack. Almost all induced draft furnaces operate with a slightly negative pressure.
Forced draft: Draft is obtained by forcing air into the furnace by means of a fan (FD fan) and ductwork. Air is often passed through an air heater; which, as the name suggests, heats the air going into the furnace in order to increase the overall efficiency of the boiler. Dampers are used to control the quantity of air admitted to the furnace. Forced draft furnaces usually have a positive pressure.
Balanced draft: Balanced draft is obtained through use of both induced and forced draft. This is more common with larger boilers where the flue gases have to travel a long distance through many boiler passes. The induced draft fan works in conjunction with the forced draft fan allowing the furnace pressure to be maintained slightly below atmospheric.

[Mel Cheeks]

Thanks it does help a little, but which one would you consider power vented. Would it be the FD explanation that is a power vented unit and are there any pictures I could look that shows the difference between an induced fan assisted units and a power vented unit.

Mel Cheeks




A little help maybe.

Boiler - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Boiler)

Controlling draft

Most boilers now depend on mechanical draft equipment rather than natural draft. This is because natural draft is subject to outside air conditions and temperature of flue gases leaving the furnace, as well as the chimney height. All these factors make proper draft hard to attain and therefore make mechanical draft equipment much more economical.
There are three types of mechanical draft:
Induced draft: This is obtained one of three ways, the first being the "stack effect" of a heated chimney, in which the flue gas is less dense than the ambient air surrounding the boiler. The denser column of ambient air forces combustion air into and through the boiler. The second method is through use of a steam jet. The steam jet oriented in the direction of flue gas flow induces flue gasses into the stack and allows for a greater flue gas velocity increasing the overall draft in the furnace. This method was common on steam driven locomotives which could not have tall chimneys. The third method is by simply using an induced draft fan (ID fan) which removes flue gases from the furnace and forces the exhaust gas up the stack. Almost all induced draft furnaces operate with a slightly negative pressure.
Forced draft: Draft is obtained by forcing air into the furnace by means of a fan (FD fan) and ductwork. Air is often passed through an air heater; which, as the name suggests, heats the air going into the furnace in order to increase the overall efficiency of the boiler. Dampers are used to control the quantity of air admitted to the furnace. Forced draft furnaces usually have a positive pressure.
Balanced draft: Balanced draft is obtained through use of both induced and forced draft. This is more common with larger boilers where the flue gases have to travel a long distance through many boiler passes. The induced draft fan works in conjunction with the forced draft fan allowing the furnace pressure to be maintained slightly below atmospheric.

[H.G. Watson, Sr.]

I guess we're supposed to guess if you're asking about Gas fired or oil fired boilers or furnaces, since we're apparently supposed to guess Boston as in Massachusetts. (Where IIRC DIYers aren't allowed even to fit pipes, let alone install a boiler or a furnace). Perhaps we're supposed to assume a different fuel, who knows?

You want a basic theory primer on which? Boilers or furnaces? Oil fired or gas fired?

Are we supposed to assume what you may or may not know about venting older less efficient boilers or furnaces, gas or oil fired?


I'm not clear as to what you're asking, and/or what your stating, let alone what your knowledge base is.

Sealed or open combustion chamber. Source of combustion air (indoor or outdoors), and sealed exhaust distance, path, direction to termination. What other mechanicals and appliances are needed or present. The area and volume containing same, etc.

Compensation for pressures, other mechanical venting present, how tightly sealed or the opposite approach - how easily infiltrated/leaky the equipment location is, distance length of run, height, and many other factors influence the "energy advisor" , safety, effectiveness, efficiency etc.

Sure there are pictures plastered all over the www, along with loads of reading material.

What do you want, and for what purpose. Narrow it down.

[Garry Sorrells]

Thanks it does help a little, but which one would you consider power vented. Would it be the FD explanation that is a power vented unit and are there any pictures I could look that shows the difference between an induced fan assisted units and a power vented unit.

Mel Cheeks


How about this to differentiate.

Induces draft is like your fire place. You build fire and the hot gas and air go up the chimney. Natural draft created by the heat from fire rising.In the boiler the heat source, gas or oil, makes a flame (fire) and the heated air and gasses rise naturaly.

The power vented boiler draws air through the fire chamber and pushes it up chimney. It draws air through boiler and pushes air hot air up chimney via a fan. It could also be viewed as an Induced Draft with Fan. In either case the stack pressure is higher than the burner chamber making the boiler a negative pressure. Therefore there is a draw of air making a negative pressure.

Now, if you take the fan and put it an orientation of pushing air into the boiler, making it a higher pressure in the burner chamber a positive pressure. That would give you a Forced Draft system. Because the air is actually forced into the heat chamber to cause/assist the draft.