Draft Inducer Remedy

Dave_144

A good friend of mine lives on the coast and has a Buderus GC124-32/5 propane fired boiler that's just a few years old. It works great until there's a Nor'easter as they produce very strong winds out of the north east. During the storm it seems like there isn't enough up draft produced in the chimney after the boiler fires, and the small safety switch in the back corner of the draft hood trips from excessive heat build up in the hood and the unit shuts down. Lesser storms with winds from all directions don't seem to cause a problem. The electric vent damper is working properly.

I feel badly for him as he previously had a nice System 2000 but it did the exact same thing. His heating company assured him the Buderus would remedy the issue and when they installed it they also cut 2 square holes in the utility room wall and added louver style vents (I think this was a hail Mary on their part, don't know if they did it during installation or after the same thing happened the first time on the new system), but unfortunately the same issue persists.

It happened again yesterday during another strong Nor'easter, we reset the safety switch today and the boiler fired right up and drafted well in the lesser winds. We were wondering if a draft inducer could be used with this boiler and if it might remedy the situation? Any thoughts or suggestions would be greatly appreciated.

kcopp

What is the chimney like? inside? Outside? masonry? b-vent? Lined? Diameter? Height?
You say he had a similar issue w/ an oil System 2k?

Dave_144

Thanks for the reply. Chimney is masonry on an outside wall, has a cap and is rectangular if I remember correctly. House has a flat roof. I'll get the height and snap a pic when the winds drop off some more. I'll also see if I can tell if it's lined with stainless, clay or what.

He had the System 2000 (set up for propane) installed by the same company when he bought the place about 10-12 years ago, and I believe it was the same issue where it would occasionally shut down during high NE winds.

HVACNUT

Get the actual chimney dimensions and height.
Is it a long horizontal run on the 6" flue?
Pitched 1/4" per ft towards the chimney?
Is the chimney straight or offset?
Possible obstruction?
The chimney must extend 3 ft above the roof, or any peak within 10 ft.

Is the basement large enough to supply adequate combustion air?
You said the transfer grills are square.
14 x 14 between the studs, or larger, and they boxed out the studs?
The input on that boiler is 132.5k BTU.
It needs 1sq. in. free air per BTU. That doesn't equate to grill size, but free air space. So double that, as the grill obviously has restrictions.
It needs 2, 14 x 20 fixed louver grills, 1 within 12" of the ceiling, 1 within 12" of the floor.

Look into "Fan In A Can" that gets wired into the burner circuit to provide combustion air to the room, and will energize before burner ignition, instead of the transfer grills.

Having the rollout switch continually tripping is a serious issue, so keep in mind, these are things to check, and recommendations if needed, not cures, as it's impossible to accurately diagnose without being on site.

A combustion analysis might point you in the right direction of the underlying problem.

Henry

We have an area here that is prone to high winds. The chimneys in that area are at least 6 feet above the roof. Also many of the older gas installations in the area have a H termination. Do what HVASCNUT says. If everything checks out, increase the height of the vent.

Dave_144

Thanks for the reply. There's a b-vent on the left side of the chimney for the boiler and a cap on the right is for a stand alone fireplace on the first floor. They look like 2 separate chimneys side by side, straight vertical run. I wasn't quite sure how to take the the b-vent off so looking down the chimney on the right for the fireplace I can see it's clay lined and 12" square. Height of the whole chimney is over 3' above the roof and not much around it to cause an obstruction. The NE wind hits the chimney at about a 45 degree angle from the left.

There's a short length of about 4" PVC protruding from the ceiling above the boiler, I'm not positive but think this may have been used to introduce outside air to the room in the past.

The 6" flue is pitched up and a fairly short run.

Where would he locate the fan in a can and where would that draw air from?

Keep in mind that this unit runs well overall, it's just when there's a very strong wind out of the NE that the problem happens. That can be as little as once a year or as many as 3-4. It's happened during the winter while he was away but luckily nothing froze up.

HVACNUT

Fan In A Can sits on the floor and brings in outdoor air.
I know you said it happened on the EK as well, but have it checked by a pro and get a combustion analysis.

JUGHNE

Given the size of the masonry chimney on the roof, would that almost constitute a small building in itself?, and also being on the corner of building it seems like the B-vent should be that magic number of 3' above where it is now.

Are we sure the B vent runs the entire length of the masonry chimney? Often the B vent 90 ell is brought out into the basement.
I have seen single wall pipe plastered into a masonry flue with only a short piece of B vent with the cap and cover on the top. Worked most of the time. FWIW

captainco

Field Controls makes a flue cap called a Star Kap. It has been tested to positively prevent the wind from blowing down it and actually increases draft slighty when the wind blows. It can be adapted. Adding more passive combustion air could make it worse because the wind could more air out than in.

If the boiler has a drafthood you DO NOT add an inducer above it or someone will get CO poisoned.

Dave_144

Thanks for the replies. Would the current B-vent be easy to remove to take a look and see what the chimney is lined with?

The wind gusts in this last storm were above 50 mph, would adding another 3' require additional anchoring?

Went to the Star Kap page and it looks like he'd also need to add a draft control in the basement and a thermal safety switch?

I came across this article on how wind can affect the pressure inside the house. Crossed my mind that if the PVC in the ceiling is still connected to the outside, maybe it's pulling air from the room during very high winds?

woodheat.org/wind-chimney.html

JUGHNE

There might not be "B" vent pipe in that chimney, perhaps just a flexible vent liner. Looks like a really long "Slinky" toy or heavy duty dryer vent aluminum hose. If you carefully lift up on the cap and top plate and don't feel a lot of weight then you might be just stretching out the flex liner.

Has the fireplace been used with the high winds? What happens with that.

Dave_144

I don't think he uses the fireplace much, it was there when he bought the place and he kept it. So not much help there unfortunately. I could have him use it during the next storm if that would be helpful?

Could it be possible that the chimney is still clay lined with just the round metal at each end?

Jamie Hall

Nobody has asked -- so I will. What is the orientation of the outside air grilles, and where are they located relative to the corners of the house? One very real possibility is that the problem isn't the wind blowing down the stack, but the pressure dropping at the air grilles and pulling the air out of the space. The amount of suction on the lee side of a building, especially at the corners, is astonishing and given the location of the chimney I'm wondering where those grilles are.

Dave_144

The louvered air grilles are in the interior utility room wall facing the hallway on the lowest level. So almost in the center of the house. You can see them on the right side of the third picture from the top that shows the boiler to the left.

newagedawn

adding 4 to six feet to the chimney will help and if all else fails you can add a draft damper down by the boiler

Dave_144

Adding on seems like a straight forward thing to try. Would you use the same top as on there now or try something like the Star Kap? And given the high winds possible, would it need to be secured additionally somehow?

Tim McElwain

Try the StarKap I have used it near the ocean on jobs for a number of years and it usually solves the problem. It even works better with a barometric in place of a draft hood and yes a spill switch is part of the kit.

Dave_144

Thanks for the reply Tim. Would you suggest using the Star Kap in place of what's there or with an additional 3' of pipe?

And that's a good suggestion on the barometric. I started reading this thread below on changing out a draft hood for a barometric and I wonder why they didn't initially install this a few years ago with a barometric instead of a draft hood? Could it be a requirement specific to this furnace?

https://forum.heatinghelp.com/discussion/162635/replace-draft-hood-with-barometric-damper-to-reduce-stack-heat-loss/p1