A few weeks ago, I described a problem with a gas fire installed in our
basement rec room. The fire is vented through a metal liner installed
in the flue of an original wood-burning fireplace. The chimney is on
the outside of the house, and when it is cold outside the chimney gets
full of cold air and there is no natural draft. In fact, there's a
downdraft in the vent.

The gas fire has a built-in draft diverter between the heat exchanger
flue gas outlet and the inlet of the chimney vent. When there is a
downdraft in the vent, the descending cold air spills out the sides of
the draft diverter. Under these conditions, when you start up the gas
fire, the combustion gases also get spilled out the sides of the draft
diverter, never making it to the vent entrance. Thus the vent never
sees any hot air, never warms up, and the downdraft continues. After a
few minutes, the gas fire shuts down because of its vent failure safety
system (a thermal switch).

What is needed is something to get hot air flowing up the chimney for a
short period, just long enough to start it heating up, and then it will
have a natural updraft that continues as long as the fire is operating.

For people with fireplaces with downdraft problems, I've seen the
suggestion of starting a paper fire at the back of the fireplace to
preheat the chimney. But there's no real way to get a flame back where
the vent starts - it is hidden behind the gas fire and accessible only
from the draft diverter vent slots on the side of the fire unit, which
are pretty narrow.

So I built a compressed air jet to get the chimney air started in the
right direction. I started with about 18 inches of 1/4 inch OD soft
copper tubing. I flattened one end and soldered it shut, then drilled a
small hole in the tubing wall near the closed end. I attached a needle
valve (the sort you'd use to supply water to a furnace humidifier or a
refrigerator icemaker) to the other end of the tube, and then connected
the needle valve inlet to a compressed air quick-connect fitting.
That's it.

When I need to use it, I bring my portable compressed air tank into the
den and connect it to the valve. Then I thread the copper tubing
through the draft diverter vent on one side of the gas fire, feeding
enough tubing to position the air outlet hole at about the centre of the
entrance to the vent duct. There is a mark on the tubing indicating
the right distance to insert it through the vent.

And then I turn on the needle valve for a little while. The small jet
of high-velocity compressed air from the tubing seems to be enough to
overcome the natural downdraft and take some of the air from the
diverter hood up the chimney with it. If the gas fire is lit, then the
hot exhaust gases start going up the chimney and a natural updraft is
soon created.

That's the theory anyway. I've only tested it once so far, since it's
only been cold enough to have a downdraft once since I built this
device, but it worked great. I think the compressed air was on
for less than a minute when I tried it. I'll do more testing when we
get more cold weather.

It's not the most convenient of solutions, since there's a portable air
tank and an air hose involved. But if it lets me use the fire on cold
evenings when a downdraft would otherwise prevent that, I'll be happy.

Dave

Hot air rises unless it is opposed by a positive pressure coming
from above. The problem you are having is that there is a negative
pressure in your house. This may be cause by furnace combustion in
the house that uses inside air instead of out. It may be caused by a
bathroom vents. It may be caused by your clothes dryer ect.

If you recently put better siding up or installed more efficient
windows your house may be tighter and facilitate a negative
pressure more easily.

The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

On Feb 16, 4:38�pm, wrote:
Hot air rises unless it is opposed by a positive pressure coming
from above. The problem you are having is that there is a negative
pressure in your house. This may be cause by furnace combustion in
the house that uses inside air instead of out. *It may be caused by a
bathroom vents. It may be caused by your clothes dryer ect.

If you recently put better siding up or installed more efficient
windows your house may be tighter and facilitate a negative
*pressure more easily.

The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

I AGREE WITH ALL OF THIS!

writes:
Hot air rises unless it is opposed by a positive pressure coming
from above. The problem you are having is that there is a negative
pressure in your house. This may be cause by furnace combustion in
the house that uses inside air instead of out. It may be caused by a
bathroom vents. It may be caused by your clothes dryer ect.

There isn't an overall negative pressure in the house, because the same
model of gas fire is also installed in the living room above the den,
vented through the same chimney (but a different flue), and it always
has an updraft. In addition, the furnace and water heater have a
direct vent to the outside for combustion air. I can even open the
front door of the house, which is only a few feet away from the den,
and there is still a downdraft in that flue of the chimmney on some
days. It happens with no vent fans running, with the clothes dryer off,
and whether or not the furnace is running.

Having said that, the pressure in the basement room almost certainly is
slightly lower than that upstairs. The basement is cooler in the
winter, and the house itself acts as a sort of chimney. The real
chimney is outside the house, so the air in the vent eventually drops to
outside temperature and provides no draft of its own. There's an
explanation of this effect at

http://www.woodheat.org/chimneys/trichim.htm

in the "Put the chimney inside the house" section.

Now, *most* the time when I try to use this fire, there is
already an updraft, or the downdraft is weak enough that the hot gases
from the gase fire overpower it and the chimney develops a proper draft
within a few minutes. Sometimes a draft isn't established on the first
try, but running the fire for a few minutes, shutting it off, leaving it
for 10 minutes, and starting it again will give a proper draft on the
second try. But sometimes (maybe 10-20%) the downdraft is strong enough
that the hot gases from the fire can't overcome it.

If you recently put better siding up or installed more efficient
windows your house may be tighter and facilitate a negative
pressure more easily.

We moved in less than a year ago and this was our first winter, so we
don't know whether the fire has always done this.

The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

There is already an outside air vent into the ceiling of the room.
There's another large vent directly through the basement wall to supply
combustion air for furnace and water heater. Even opening the main door
of the house, 10 feet away from this room and half a floor higher, does
not eliminate the downdraft on cold days. Even with plenty of access to
cold air from other outside sources, there's still a downdraft in the
chimney sometimes.

Dave

On Feb 16, 5:49 pm, " wrote:
On Feb 16, 4:38?pm, wrote:

Hot air rises unless it is opposed by a positive pressure coming
from above. The problem you are having is that there is a negative
pressure in your house. This may be cause by furnace combustion in
the house that uses inside air instead of out. ?It may be caused by a
bathroom vents. It may be caused by your clothes dryer ect.

If you recently put better siding up or installed more efficient
windows your house may be tighter and facilitate a negative
?pressure more easily.

The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

I AGREE WITH ALL OF THIS!

open a door or window when you light the fire until the draft gets
going
Mark

The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

There is already an outside air vent into the ceiling of the room.
There's another large vent directly through the basement wall to supply
combustion air for furnace and water heater. Even opening the main door
of the house, 10 feet away from this room and half a floor higher, does
not eliminate the downdraft on cold days. Even with plenty of access to
cold air from other outside sources, there's still a downdraft in the
chimney sometimes.

http://healthandenergy.com/backdrafting_of_chimneys.htm

Then your solution should also include ventilation to equalize the
temperature/pressure between upstairs and downstairs. This should
minimize the "stack" effect.

There is also the possibility that your flue opening is on the
windward side of your house which can cause pressurized are to flow
down the flue.

wrote:
The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

There is already an outside air vent into the ceiling of the room.
There's another large vent directly through the basement wall to supply
combustion air for furnace and water heater. Even opening the main door
of the house, 10 feet away from this room and half a floor higher, does
not eliminate the downdraft on cold days. Even with plenty of access to
cold air from other outside sources, there's still a downdraft in the
chimney sometimes.

http://healthandenergy.com/backdrafting_of_chimneys.htm

Then your solution should also include ventilation to equalize the
temperature/pressure between upstairs and downstairs. This should
minimize the "stack" effect.

There is also the possibility that your flue opening is on the
windward side of your house which can cause pressurized are to flow
down the flue.


I saw a house on TV a while back that had this problem and I think the
solution was to install a small fan made for this purpose on the top
of the chimney.

On Fri, 16 Feb 2007 19:59:44 -0500, wrote:


The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

There is already an outside air vent into the ceiling of the room.
There's another large vent directly through the basement wall to supply
combustion air for furnace and water heater. Even opening the main door
of the house, 10 feet away from this room and half a floor higher, does
not eliminate the downdraft on cold days. Even with plenty of access to
cold air from other outside sources, there's still a downdraft in the
chimney sometimes.

http://healthandenergy.com/backdrafting_of_chimneys.htm

Then your solution should also include ventilation to equalize the
temperature/pressure between upstairs and downstairs. This should
minimize the "stack" effect.

There is also the possibility that your flue opening is on the
windward side of your house which can cause pressurized are to flow
down the flue.


If all else fails...Jimmy Rig......If possible rig a fan to draw
air into the house as close to the offending flue as you can. Just
pressurize the house in this manner for five minutes before lighting
the fire.

On 16 Feb 2007 17:10:57 -0800, wrote:


wrote:
The solution is to either use outside air for your fireplace or
install some sort of vent in the wall of the house to eliminate
your negative pressure. Maybe both?

There is already an outside air vent into the ceiling of the room.
There's another large vent directly through the basement wall to supply
combustion air for furnace and water heater. Even opening the main door
of the house, 10 feet away from this room and half a floor higher, does
not eliminate the downdraft on cold days. Even with plenty of access to
cold air from other outside sources, there's still a downdraft in the
chimney sometimes.

http://healthandenergy.com/backdrafting_of_chimneys.htm

Then your solution should also include ventilation to equalize the
temperature/pressure between upstairs and downstairs. This should
minimize the "stack" effect.

There is also the possibility that your flue opening is on the
windward side of your house which can cause pressurized are to flow
down the flue.


I saw a house on TV a while back that had this problem and I think the
solution was to install a small fan made for this purpose on the top
of the chimney.

Restaurants sometimes use this type of fan for safety reasons, but it
will definitely create a upward draft.

http://www.fluesystems.com/fans/chimney_top_fans.htm

writes:

Then your solution should also include ventilation to equalize the
temperature/pressure between upstairs and downstairs. This should
minimize the "stack" effect.

The main entrance to the house has a half-flight of stairs up to the
living room, and a half-flight down to the den. This stairway is always
open. About the only way to improve ventilation further between living
room and den is to cut a large hole in the floor between the two rooms.

There is also the possibility that your flue opening is on the
windward side of your house which can cause pressurized are to flow
down the flue.

Could be, but both flues are in the same chimney.

Dave

http://www.fluesystems.com/fans/

http://www.chimneyfans.com/

Then your solution should also include ventilation to equalize the
temperature/pressure between upstairs and downstairs. This should
minimize the "stack" effect.

The main entrance to the house has a half-flight of stairs up to the
living room, and a half-flight down to the den. This stairway is always
open. About the only way to improve ventilation further between living
room and den is to cut a large hole in the floor between the two rooms.

I once had as wood stove in the basement and needed to exhaust
some of the heat out of immediate area. I cut a hole in the ceiling
close to the front of the stove. Upstairs this hole was at the end of
a bedroom hallway. This vent had a fan included. You need a vent
like this that will allow you to draw air into the basement upon
starting the fire. Hopefully this will be enough to equalize the
pressure/temp difference between upstairs and downstairs.

(Dave Martindale) writes:

And then I turn on the needle valve for a little while. The small jet
of high-velocity compressed air from the tubing seems to be enough to
overcome the natural downdraft and take some of the air from the
diverter hood up the chimney with it. If the gas fire is lit, then the
hot exhaust gases start going up the chimney and a natural updraft is
soon created.

An update: I've used this gadget twice more when there was a downdraft
in the chimney. It seems to work really well. A 10-second shot of
compressed air seems to be sufficient to draw some of the warm exhaust
from the fire into the chimney vent. Once the warm air reaches the
vent, it starts warming it up and a natural updraft takes over.

It takes so little volume compressed air to reverse the downdraft that
if I was doing this over again, I might try to use a "dust gun" can as
the gas source. And the quarter-inch copper tubing is vastly oversized
for this use; a length of copper capillary tubing from a dead
refrigerator or dehumidifier might be sufficient.

Dave

replying to Dave Martindale, Roberto Zavattiero wrote:

highly recommended solution
http://www.homeownershub.com/img/7u
http://www.homeownershub.com/img/7v