flue pipe bend causing Carbon Monoxide?

Technical questions that one would like posed to experts
(scientists) in fields related to particulate pollution.

flue pipe bend causing Carbon Monoxide?

Postby buckman » Tue Nov 21, 2006 1:58 am

We have just bought a multi-fuel stove to replace our older smaller one and wondered your thoughts on our situation.

The newer stove is much taller, and it has the flue hole in the centre of the stove and therefore we were told we would need a small S bend (well 2 x 90 degree bends) for the flue (draw smoke). We don’t have a flue hatch for this to be cleaned, which the company knew about when we ordered the fire and sent them all the photos, dimensions for the flue pipe to be created.

We went to have this fitted by a HETAS registered fitter and he said that the pipe we had made by the fire company was actually illegal! As we couldn’t get in to clean the chimney once it was all fitted, the soot and deposits from the chimney would block the 1st 90 degree bend and would cause a build up of Carbon Monoxide!

Can anybody clarify this? And whats the best way to use a small pipe for our very slight bend as there is a slight offset between the top of the stove hole, and the register plate hole in our chimney?
Posts: 1
Joined: Tue Nov 21, 2006 1:57 am

S bend and CO

Postby JackPine » Tue Nov 21, 2006 9:14 am

From a design standpoint, yes, the S bend using 2 90's could cause an issue with solid material filling up the 90 just under the stack and not allowing the flue gas to go up the stack. This back-up would cause the products of combustion to go into the house instead of up the stack.

Another danger is a chimney fire. Even if the pipe does not get plugged completely, there could be an accumulation of soot/creosote debris which could catch fire in the flue. As you are well aware, this is dangerous.

One solution to your problem by some on this board would be to get rid of your new multifuel boiler and only use fuel oil or gas. And yes, that would solve the problem with soot backing up your S bend.

However, since you just bought the boiler and I am sure you want to keep it, an option is to install "T" under the stack on its side. The question is do you have enough room between the bottom of the register plate and the top of the boiler? How it would work is you put a clean out area under the vertical part of the T (which is now on its side with the top part now in line with the chimney) so any debris falling down the chimney goes straight down. The flue gas goes out of top of the boiler, through one 90 at the top of the boiler, into the horizontal part of the T (which is on its side remember) and up the stack. I would connect the bottom part of the T to an air tight box behind the boiler. The box would have a door so you could clean out any debris. I would also use bolts and gaskets so you could remove the box (keep the T in place if you wanted to) and run a chimney cleaning brush up the chimney. If your tolerances are too tight, other than having a diagonal piece of pipe fabricated to run from the top of the boiler to the register plate, I don't have any ideas yet.
Posts: 38
Joined: Fri Oct 20, 2006 11:54 am
Location: Northeast

Multi-fuel stove: s-bend, carbon monoxide, and soot.

Postby pm2.5mary » Thu Nov 23, 2006 12:27 pm

We are delighted to hear that you have the option to burn cleaner fuels, and there are very good reasons for doing so! Or does multi-fuel mean something else? Did you buy from a reputable company that will help you switch to a cleaner fuel stove such as oil or gas, since your situation does not work with the large amount of soot a solid fuel would generate?

Did Mr. Pine suggest that there would not be a soot build-up problem with oil and gas? He is right.

Cleaner fuels are not just a little bit better in terms of emmisions, but many orders of magnitude better. Burning wood as your fuel means that you are living in high levels of carbon monoxide in addition to a toxic mix of many of the same chemicals that are in cigarette smoke, just more of them. The problem with these emmisions is that they are so small that they can't be cleaned up, and they are in a gaseous form that can be inhaled and circulate directly in your blood stream. 'But my stove is airtight' I often hear. That may be so, but this areosol is heavier than air and usually sinks towards the ground and according to Larson, Ott, Cass and many other researchers, 70% of the sub-micron toxic soot seeps right back into the building envelope.

(Just because a stove is EPA Certified does not mean that the soot that is puts out is safe to breathe.)
"Particulate pollution is the most important contaminant in our air. ...we know that when particle levels go up, people die. " (Joel Schwartz, Ph.D., Harvard School of Public Health, E Magazine, Sept./Oct. 2002)
Find more at http://burningissues.org
User avatar
Posts: 320
Joined: Sun Oct 15, 2006 6:04 pm

no carbon monoxide

Postby woodburner » Tue Nov 28, 2006 6:58 am

Mary, my oil furnace does create soot that needs to be cleaned every year just like my wood stove chimney needs to be cleaned. Also if you have carbon monoxide in your home because you are burning wood, you have a major problem. I primarily burn wood and have a carbon monoxide level of zero at all times in my home.
Posts: 203
Joined: Mon Oct 16, 2006 4:37 am
Location: Upstate NY

CO in house

Postby JackPine » Tue Nov 28, 2006 8:32 am

Mary, woodburner is correct. High levels of CO in a house mean the furnace/boiler/stove has serious problems. Properly installed wood stoves do not emit any more CO in a house than properly installed furnaces and boilers. If there is a draft on the chimney/flue, the pollutants will be pulled up and out. One thing which must be mentioned is that on very windy days, there may be a slight backdraft now and then. This will happen with each of the heat sources, not just wood stoves.
Posts: 38
Joined: Fri Oct 20, 2006 11:54 am
Location: Northeast

Postby The Professor » Tue Dec 05, 2006 10:38 pm


I used to live jn your neck of the woods (Groton CT) and converted my two car garage into a family room. We invested in a high end wood burning stove. I can't remember any of the particulars other than it was the most efficient stove available in 1986. I soon noted that when burning I felt similar to when I was at sea on a submerged submarine where we had a constant CO problem. Many of my neighbors also burned and I began to realize that I felt better when traveling than when at home.

This realization was a major factor in my returning to San Diego. I have fully natural gas house including my fireplace and grill (haven't purchased propane or charcoal in years).

I live due east of FriendofAir (we have talked but not met) and am several hundred feet above him in elevation. Because of the topology in this area it does not take much to smoke out a neighborhood. In the Central Valley of California in and around Fresno, they have bans on woodburning because of the bowl effect and the impact of trapped wood smoke. While I am aware of your personal views on the matter we have numerous stores here in the area that promote wood burning stoves and fire pits.
The Professor
Posts: 4
Joined: Sat Oct 28, 2006 10:55 pm
Location: San Diego

CO on submarine

Postby JackPine » Wed Dec 06, 2006 6:35 am


Thank you for serving our country. I have worked with a few former submariners and they were all top notch.

Are you sure you had CO issues on a submarine? I didn't think they allowed combustion on those boats, for CO is emitted from combustion sources, not people. Did they allow smoking while submerged in '86? Maybe you mean CO2.

I can see a CO or CO2 issue in an area from too many combustion units of any type and the right (which is wrong, if you get my drift) weather conditions and geographical features. This would be like the bowl you were describing. If there were CO or CO2 problems outside the house in the ambient air, then there would be problems inside the house as well because the outside air would be drawn in due to the chimney draft.

My point was, if there was sufficient draft, any products of combustion would be drawn OUT of the house and not escape into the house. The one caveat was if there were small backdrafts on windy days.
Posts: 38
Joined: Fri Oct 20, 2006 11:54 am
Location: Northeast

CO readings

Postby ME-air » Wed Dec 06, 2006 8:13 am

In my job capacity I have access to both CO2 meters and CO meters. Fortunately I have been able to use them both at a house with a woodstove used for 80% of the heating needs, another house which used only natural gas and one which used only oil. Now granted, these were only three houses and not a large enough data set, but what I noticed was interesting:

CO2 levels in the woodburning house were 430 ppm.
CO2 levels in the gas burning house were 520 ppm.
CO2 levels in the oil burning house were 540 ppm.

Outside air is typically 380 ppm in this area, average for the world as a whole based on Mauana Loa Observatory data. There are so many explainations and reasons for the house data that there is not enough room here to go over them all. None of the houses had an air exchanger installed and all of them were built after 1990.

CO levels in the woodburning house were 0 ppm.
CO levels in the gas burning house were 5 ppm.
CO levels in the oil burning house were 0 ppm.

I can explain the 5 ppm in the gas house: the ductwork running the flue gas to the outside of the house was not installed properly so it was leaking CO into the basement and that went through the house. This unit was direct vent (i.e. no chimney). We fixed the ductwork and the CO was down to 0 ppm the next day. CO levels outside each of the houses was 0 ppm. Fortunately for each of the homeowners they are not located on a busy road where mobile source CO emissions are typically higher. I did not take the outside reading for the gas burning house on the same side as where the furnace vented.

Since all of these reading were taken on days with good weather for dispersion, there could be days when CO outside is higher. Plus, there could be locations beside each house which could have localized higher CO emissions as a result of the heat source combusting its fuel. However, since the average CO ppm in Maine is less than 1, I believe the outside readings are typical.
Posts: 13
Joined: Mon Nov 20, 2006 1:46 pm
Location: Maine

Return to For the Experts

Who is online

Users browsing this forum: No registered users and 0 guests