Why Is a Power Vent Necessary?

I understand the application of the power vent and it's responsibility for creating draft, but can someone explain to me why it's necessary if you're running a full-time combustion blower? If you view the fire box as a "sealed" compartment, you're going to induce a high pressure inside the box via the forcing of air into the box from the combusion blower, which must exit out somewhere and the path of least resistance is the flue pipe. I understand the need for the barometric damper still to regulate the amount of draft that may exeed the artificial draft you're creating by forcing air into the box, but I'm a little confused on why you would still need a fan to create an artificial draft in the chimney.

pconn171 wrote:I understand the application of the power vent and it's responsibility for creating draft, but can someone explain to me why it's necessary if you're running a full-time combustion blower? If you view the fire box as a "sealed" compartment, you're going to induce a high pressure inside the box via the forcing of air into the box from the combusion blower, which must exit out somewhere and the path of least resistance is the flue pipe. I understand the need for the barometric damper still to regulate the amount of draft that may exeed the artificial draft you're creating by forcing air into the box, but I'm a little confused on why you would still need a fan to create an artificial draft in the chimney.

It is for saftey reasons, you want the firebox under negative pressure at all times. Without the chimney draft the firebox would become pressurized as you are pushing a greater volume of air than the chimney can discharge without being "pushed out" and the risk of CO escaping to your living space is not an attractive option. Some units use a blower on the exhaust side of the firebox, this will maintain a negative pressure in the firebox itself.

It for places where you don't have or cannot run a full height chimney. A power vent only needs to terminate just outside the house. Since its forced draft, there is no need for a full height chimney. this is an option for many people without chimneys or cannot utililize existing chimneys.

I run both. My Hyfire uses the standard block chimney (35' high) and my keystoker uses a power vent, just thru the outside wall in the garage.

If you have a short chimney, without the power vent, you cannot create enough draft to pull all the fumes out of the stove and possibly leaking into the house thru the stove or baro damper as stated above.

With a standard chimney, the more heat you have, the higher the draft. Therefore, the baro will open more when the stove is really cranking or when its really cold outside, since heat rises faster if the temp is colder outside. My baro on my Hyfire is normally 1/4-1/2 open all the time due the good draft of the chimney.

coaledsweat wrote:It is for saftey reasons, you want the firebox under negative pressure at all times. Without the chimney draft the firebox would become pressurized as you are pushing a greater volume of air than the chimney can discharge without being "pushed out" and the risk of CO escaping to your living space is not an attractive option. Some units use a blower on the exhaust side of the firebox, this will maintain a negative pressure in the firebox itself.

This is all the explanation I needed. Functionally, it doesn't matter, but for guaranteeing the exhaust of CO2 makes a lot of sense. If the box wasn't 100% airtight (which is probably true for every stoker out there) some CO2 would escape into the room. Thanks - got it.

While C02 can be a problem. The real concern is CO.
You will never even notice CO2 around you at 1000ppm. CO at 200ppm will affect mental capacity. 400ppm will cause head aches. 800ppm will knock you unconscious in less than 2hrs.1600ppm will kill you as dead as a hammer in an hour or two at most.10,000ppm will put you on the floor unconscious after 2-3 breaths.

CO = Carbon Monoxide the killer
CO2 = Carbon Dioxide the Greenhouse gas

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Either can be deadly but the significant difference between the two is that CO bonds with your hemoglobin so even if you're taken out of the environment your body is still starving for oxygen. Interestingly Carbon Dioxide at larger concentrations can even be beneficial under some circumstances:

http://www.epa.gov/ozone/snap/fire/co2/co2report.html
In human subjects exposed to low concentrations (less than 4 percent) of carbon dioxide for up to 30 minutes, dilation of cerebral blood vessels, increased pulmonary ventilation, and increased oxygen delivery to the tissues were observed (Gibbs et al. 1943, Patterson et al. 1955). These data suggest that carbon dioxide exposure can aid in counteracting effects (i.e., impaired brain function) of exposure to an oxygen-deficient atmosphere (Gibbs et al. 1943).