High Altitude Draft Issues

Rusty Smith

Hello ,
I was given your info from my heating guy who suggested I get an opinion other than ours on a difficult problem.
I have a Tarm boiler which is wood fired primary and propane secondary heated. The wood fired part is working
acceptably with one issue which is probably tied to my major problem the propane burner. My house is at 10,700 ft.
We typically get winds up there in the 90-100+ mph range. We have had problems from the first with the propane
burner mysteriously going out and going into latch out mode. When it is manually reset it fires right up. The burner is
a Carlin EZ burner. We adjusted the orifice for altitude and the products of combustion are within the guidelines except
the oxygen. We're burning slightly lean. I talked to Carlin and we thought maybe the burner control relays were the
problem but that wasn't the case. It did the same thing when I replaced the control unit. After I replaced the control unit
I decided to stay around and see if I could figure out what was happening. The burner would cut out with severe wind gusts.
I have a woodstove and started watching that as well. We seem to be in an area where downdrafts are created when the
wind is right and they are huge. We have a barometric damper on the boiler flue and that thing bangs open when the downdraft hits.
I think the downdrafts are blowing the flame off the flame rod and dropping out the burner. I put this to the test on a "normal"
day and the burner cycled on and off just like it's supposed to. Wind was probably 20-30 mph that day.
Here's our dilema. The chimney is high enough given the usual guidelines. To get it above the downdrafts I probably have to get
above the treeline which isn't possible. I talked to the draft cap guys and they thought the problem was too severe to solve with
their devices. I'm looking at putting an exhaust-o fan on top of the chimney. This should eliminate the downdrafts but I have a buildup
of icicles from the wood burning on the present chimney cap. We are worried that if we don't get the flue gases hot enough we'll
ice up the fan and be back where we started. Another option we're considering is to put a fan upstream in the chimney and put
a draft cap on top. That might solve the problem and avoid the icing issue. I also think that if we get the right draft we may not
have the icing issue anyway. Remember I said the wood has only one issue. I can't get the flue up to the boiler's recommended
temperature. I've gotten it into the "normal" range a couple of times but mostly its running about 250F where they recommend
about 500F. I suspect that this is the reason the ice is forming. All of this points back to a lack of draft and downdrafts as the culprit.
We'd like to get your input before we dive off again.
Have a Happy New Year. Thanks for any help.
Rusty Smith

don_185

Out side

Outside boilers or in a mechanical room.You may have to add a fan and keep the room under a positive pressure.

Rusty Smith

Don,
The boiler is in the garage. We have (2) 6 inch round vents
for the combustion air. Interesting idea but not sure how I'd get everything sealed up well enough.
Thanks,
Rusty

don_185

I take

I take it you have a wood boiler that can fire would or propane..is that correct?

I've installed several tarm wood boiler at sea level and they draft their butts off even when they are cold.

Only a 250 stack temps.That may be from the wood you are using.

Check that draft with the garage door open then, again wtih it closed.Also check the draft agin when the wood goes out and the propane kicks in.

In short..break out the marshmellow we may be here awhile.

Rusty Smith

Don,
I've tried it with the doors open. No effect. If I have
a bunch of Douglas fir I can get it close to 400F. On spruce
and pine I max out about 250F. Wood definitely affects it.
On propane it runs about 250F. I've seen that as low as 210F. The other thing that might be of interest is it is
cold natured as hell. We're still building this house and
when I've come in and the propane is out the water temp
in my tanks is down to 100F. It takes 1 1/2 to 2 hours to
get that thing heated back up so I can have any kind of reasonable combustion. I get a roaring fire in the box, close the door, turn on the draft fan and it actually kills
my fire!! I do this 3 or 4 times until the water temp gets up to 140 or so and I can finally get the thing to stay lit.
Seems awfully strange to me but during this period of heat
up I fill the garage with smoke. Smoke comes out everywhere-
from the top and bottom doors, around the damper, out the propane burner. It's a real pain but once you get er going
all you have to do is stoke that baby and she heats water like crazy. Another piece of info for you is when the temp
is at 250 in the flue the water temp is 175-185 about. That
seems to be where it should be. I have 2 2500 gallon storage tanks in the basement. I'm trying not to use the propane at all but at some point I may need it if I can't get back in to the house. We get a boatload of snow up there. Any more ideas or input is appreciated. have a Happy New Year.
Rusty

don_201

Thats stack

Thats stack temp is too low for propane.You either derated the propane burner to much or, you may have not had to derate the burner at all.

I not sure if you could ever get control with a propane burner sharing the same firebox as the wood stove.

Would you care to share any other numbers like your 02,co and excess air when the propane burner is running.Just what is the density of the air that high?

Mark Custis

Draft is draft

you do not have it. Start over. You are not heating the flue enough. Make it hot and it will draft.

Mark Eatherton

Could be a multitude of issues...

Try opening a door to the outside when you are trying to light a wood fire.

Once lit, and draft established, the gasifier fan should be able to maintain and enhance draft.

The LP burner may be seeing a back draft condition that is causing the burner flame to snuff. Make darned sure you have a spill switch at the outlet (inlet) of the barometric damper.

There are numerous manufacturers of omni directional vent caps that will (theoretically) avoid any down draft conditions.

ME

Mark Custis

The laws stay the same

even if you ar up in the sky. Hot goes to cold.

Glen

another view

draft at that altitude with the winds mentioned can be a bit of a bugger to track down. even the slightest breeze can counteract the drafting of your heating plant. I ran into this issue a few years ago in the arctic - darn boiler would work fine until wind picked up. To solve this we used a gizmo on top of the chimney - it would swivel with the wind direction and always kept the flue outlet on the lee side. something to consider. On the down side I do not recall the name of the product. Once the down drafting is minimized you can work on the other issues you mentioned.

R.Bell

Hi-Draft

I believe this would work for you - used by the Swiss in mountain top Chalets for many years with great success - it is designed an built in Switzerland as well.
Made of Stainless Steel - works with wood, oil, or gas heating systems.

See attached pictures.

Fred Harwood_2

High

GD, Rusty, but you live way up there. Do you keep oxygen handy? Even for visitors?

One other possibility: strong winds across a straw (chimney) create very strong drafts, not down-drafts, that bang OPEN the barometric vent, and suck the flames right off the irons.

Stabilizing the effect with simple hoods opening away from the wind can be difficult. Hoods designed for breaking the sudden draft might be the ticket to high heating bliss. Unfortunately, I don't know of any.