chimney help please

Unknown

Bob:

I has a similar problem a few years ago. I finally figured out that the house was a modular. When it had been assembled, the two sections were not drawn up tightly allowing a massive vertical chimney directly to the attic.

We boarded up the opening and had no further problem.

Bob Gagnon plumbing and heating

chimney help please!

I got a call yesterday for a boiler I installed this summer that shut off on the roll out thermal switch. When I arrived the chimney was back drafting, non-stop, like it was from a powerful fan. Here is the specifics, 80% efficency cast iorn boiler, with a standing pilot. A 35' chimney, clay lined, 3' above the peak, on an outside wall. Over the summer homeowner installed 2- 4" pipes for make-up air, and ran 1 high at the ceiling and 1 low, near the back of the boiler. I put my torch to try to prime the chimney, like I do for my wood stove, and change the flow direction, but it was a non-stop powerful down draft, until the homeowner opened the basement door, instantly I had powerful draft UP the chimney, even before the chimney had time to heat up. closing the basement door and the draft reversed direction instantly to a down draft. opening a window 8' from the boiler only decreased the down draft a little. The house has an air exchange system that we shut off but that had no effect on the chimney at all. The house also had a whole house fan, but of course it wasn't on yesterday, and had a closed shutter. The house has standard construction 2X4 with fiberglass insulation and Tyvek. The weather yesterday was overcast with no wind. Any ideas what I should look for, thanks in advance, Bob Gagnon

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Unknown

Bob short of

doing a blower door test try this.

Bring on every exhaust fan in the house, shut all windows and doors, make sure the fireplace damper is closed. Do they have a Jenn-Air unit if so bring it on along with the dryer. You have created the worst possible situation. Now bring on all the gas/oil equipment in the house. With a draft gauge see what you have happening above the draft hood on the boiler. It should have a -.01, -.02 draft. If it is continuing to spill now shut off each exhaust one at a time and see if it changes.

If I read what you are saying you have a negative condition at all times is that correct? If doing the previous test did not see any change then the building needs mechanical dedicated air input to make up the air loss from the building.

It sounds like the installtion of the air for combustion 2 - 4" pipes has changed the pressure in the building somehow or perhaps it was bad before and they are not adequate.

What is the total BTU's in the boiler area? Try one other thing, block off the two 4" units with the same test of everything running and then every thing shut off see if it makes a difference. The fact that the chimney is an outside chimney and 35' tall does not help.

Is the draft hood on the boiler built in or above the unit? Try blocking the draft hood also to see if it changes the operation. It may be necessary to remove the draft hood and install a barometric along with a Star-Kap on the chimney and bring in mechanical dedicated air.

Empire_2

cross breeze

I wondering if with the MUA unit that it is creating a cross breeze thru the basement area?...When opening the door to the tightly sealed basement breakes the seal and allows the chimney to again begin to draft. Just a thought. Mike T... Try to completly block off ther air exchanger intake and exhaust and see what happens, with basement door open and closed.

[Deleted User]

Does the basement door...

open up to the upstairs or to the outside??

If to the outside, go to the top floor and look for some type of natural ventilation that would allow a chimney effect to occur inside of the building. This would be the one case where the saying "heat rises" makes a LOT of sense.

Short of that, get yourself a liquid smoke generator and "see" where the draft action that is greater than the chimneys draft action is coming from. The chimney is obviously relieving a natural or mechanical draft greater than it can create itself.

Thank goodness for roll out switches.

I know this goes without the need to say it Bob, but get back to us with the definitive answer and solution.

And remember this Holohanism, "The solution to the problem is rarely in the same room as the problem..."

ME

jim lockard

Draft gauge

Bob- Could you maybe drill a 1/4 " hole in the basement door and with the door closed and furnace on get a draft reading ? I suspect you will get a negative which will then tell you to add more air. Best Wishes J.Lockard

Weezbo

a thought...

go outside look at the chimney, see any little metal door anywhere around the base? i am speculating here, that there is one and indeed is the true source of the pressure imbalance in the flue.

jim lockard

Could be

Weezbo the holy chimney

Bob Gagnon plumbing and heating

more details

thanks for all your help. The boiler and water heater, app. 140,000 BTU'S, vented properly all summer. The homeowner has multiple low level CO detectors. I removed the 4" makeup air pipe, that went down to the floor, so both 4" MUA will pull into the house. I opened the basement door, fired the boiler, and with the extra MUA, venting has worked good since yesterday. I thought about the chimney effect creating a vacuum in the house, but the attic showed nothing unusual. I was thinking of installing mechanical MUA but thought I might be treating the symptom, not the problem. I have never seen a basement with a vacuum like this. I will try blocking the 4" MUA holes and see if that has any effect. Mark, how would I do that smoke test? Just rent a machine, fire it up in the basement, and look for the holes with smoke rising up in the attic? Then, would I seal the holes? This house is 15 years old and no pipes or wires are sealed. The chimney has a cleanout door on the inside of the basement and it was closed tight.
Thanks again, Bob Gagnon

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[Deleted User]

Here ya go Bob...

http://www.metermall.com/Search/Smoke.htm

I have heard of the chimney effect in the chases of houses, but usually only during a fire.

Like they say, "Just when you think you've seen everything..."

ME

johnl45

Exposed tile lined chimney with no liner? Better check that National fuel gas code.

Joel_3

hey bob

I'm in Mass and have a blower door aren't you close to me ? if so I could possably come do some testing on the house . From expierence i can tell you that you probably have alot of leaks at the attic floor over powering the chimney. I just had a house pull negative 6 pascals in the chimney with two bath fans on . Many natural draft gas appliances are all done at negative 3 pascals . For point of reference one inch of water is 250 pascals , so we're talking very little pressure to screw you over . This is becoming a pretty big problem as newer equipment has more safety's on it.

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Bob Harper

depressurization testing

What Timmie described is a Worst Case Depressurization test. It's best to perform this with a digital micromanometer that can read to a 1/10th Pascal with time averaging to buffer wide swings but even a simple smoke puffer will do. I like the TT puffer because of its size.

Keep in mind a chimney is just a "dumb duct" to quote Dave Hill, of Eneready, B.C. It is the pressure gradient that determines which way air & gases will flow. If its flowing back in, you either have too much negative inside or too much positive outside.

To correct the house, your mantra is "tight up top/ loose down low". The top of the thermal envelope should be as tight as tupperware. That whole house fan can be a huge leak. Add to that canned ceiling lights (esp. if not I.C. or Insulation Contact rated), ceiling fan boxes, bath room fart fans, speakers, and attic access doors. One huge killer is supply leaks in forced air distribution systems located outside the thermal envelope of the house. Don't guess--test! As for basements, since you have hot water, look to clothes dryers, the kitchen Suck-O-matic, central vac., etc. All upstairs windows should not only be closed but latched to compress the gaskets if newer windows. In houses with ducts, you'll want those ducts sealed. Return leaks, esp. filter slots should be sealed ( which is required btw in '54).
Now, provide makeup air to satisfy the house once these measures have been taken. Start by opening a door or window in the basement and noting the size opening it took to satisfy the house. Now install a MUA system based on this.

One of the changes since summer is stack effect. I've seen plenty of houses with enough stack effect to backdraft water heaters and fireplaces without any of the other aforementioned factors.

One you have the house fixed, the chimney should work. Then, plan on relining it ASAP to make it more spill resistant as long as properly sized.

If the prevailing wind is such that those MUA's are in the leeward side, they will become exhausts, which is why passive air is so unpredictable. Just think about it: MUA on fireplaces cannot be above the inlet and on masonry fireplaces, it carries a 1" clearance to combustibles for the first 5ft. A clearance on a MUA? Its because they can backdraft sucking fire into the duct! I've seen flames shooting out of a MUA inlet!

As for the positive pressure outside, look to roof angles, adjacent structures, and wind. Try increasing the stack height and use a more aerodynamic cap. The Star cap from Field is good for metallic vents.
HTH