Chimneys and Flues

captainco

I have heard many discussions on flues as to sizing, condensation and corrosion. I am writing knowing full well that there will be some crazy discussion including some of my best students. It is my best wish that it will be educational.

I have been combustion testing for over 40 years, industrial, commercial and residential installations. Not once in 40 years have I found a flue that was too big! Now when I here people say they are too big is that because the don't understand venting or they don't understand draft?

The only function of a chimney is to communicate the outdoor temperature and pressure with the indoor temperature and pressure. Does the diameter of the flue change any of those? Most say that if the chimney is too big then the cold air cools the flue gases or blocks their escape. The question here is why does a 100' tall chimney have higher draft than a 20' chimney. It contains quite bit more cold air. Then there is the fact that chimneys are warmer in the summer and yet the draft is very low. The fact is cold air displaces hot air. The more cold air the higher the draft!

Draft is created by temperature difference and pressure difference. Thanks goodness temperature overrides pressure or we would be killing everybody. Mechanical rooms are supposed to be positive pressure or greater than outdoors but most approved installations according to Code are negative. How can you pull air in from a grille or pipe from outside without making the room negative? When we have venting problems how often is that the real problem rather than flue size?

Today there is the argument that flue gas temperatures of newer equipment are lower than old equipment. The exit from the heat exchange may be cooler but the temperature in the flue is hotter because the is no drafthood diluting the temperatures, I have rarely tested the flue temperature above a drafthood appliance that was above 300 degrees. If new equipment doesn't have temperatures above 300 degrees there is something wrong.

Orphaned water have grown up and know how to vent on their own. They have done it most of their life because they come on many; many times when the heating equipment is idle. Water heaters are the equipment that keeps the air in the flue warmer, not the furnace.

Condensation and corrosion are caused by improper venting but never by a chimney that is too big! Most don't realized the current venting tables were created by a computer and were never tested in the field. But then they say you can't use them except in a steady state environment.

I just felt that it is time to have a real discussion on venting, combustion air and chimneys and how to fix problems rather than adding bandades.

Jamie Hall

Interesting thoughts, @captainco . And I'm not going to weight in too heavily on the fired appliance side of this. I will observe, however, that in the case of fireplaces there is a significant problem with flues which are too large or are poorly constructed: they can and sometimes do back druaght into the house. This has nothing at all to do with a negative pressure difference directly involving the flue size -- but in some cases may be due to aerodynamic effects of wind around and over a structure or roof, which can cause surprisingly large pressure differences around and over the building locally. However, Count Rumford, back in 1795, figured out that part of the problem with existing fireplaces (only part of the problem -- the other main problem was that they were much too deep for their width, a condition which is as true of most fireplaces today as it was more than 200 years ago -- folks and building codes are slow learners) was that if the flue is too large, there would be a counter circulation of cold air coming down one side of the flue, while a circulation of warm air (smoke) went up the other side -- and one of his improvements was the incorporation of a smoke shelf in the flue which confined the smoke from the fire to a relatively small area on one side of the otherwise large flue, and allowed the cold countercurrent to turn at the smoke shelf, mix with the smoke, and go back out the chimney rather than blowing the smoke back into the room.

A fireplace designed in accordance with Count Rumford's principles will not smoke, even in very adverse wind conditions, and will be a positive heat source to the space, rather than negative.

captainco

I guess they still must be building fireplaces incorrectly because I still get quite a few calls on fireplaces smoking up places.
Not sure if the Count was familiar with laminar flow. This is the definition of heat traveling through the center of a vessel while cooler air surrounds it. Bob H knows more about fireplaces than I will ever know and I will admit it is not my specialty. But furnaces and boilers not venting is something I have encountered tens of thousands of times, In no case was there too big of a flue.
Thanks for your input, I am going to have to learn something new!!

MikeL_2

     Captainco, 
            I'm not a fan of crazy discussion, but I do appreciate sharing ideas, experiences, processes, successes, documented data, and policies that generate discussion and provide an opportunity for learning. 
             Should I disregard the 7 times rule for combustion venting?

Jamie Hall

They are still building them wrong, @captainco ! Just to give you the idea of a Rumford, though, I just measured the main fireplace in Cedric's home -- which behaves beautifully. It is 18 inches deep from the front of the fireplace, and the sides are angled at 45 degrees in ward. The back wall is 4 feet wide, so the front opening is 7 feet wide. It's about 3 feet high. The flue opening from the fireplace is 6 inches front to back, set about 4 inches back from the front (the back wall slopes forward to meet it), and about 18 inches wide. There is a 6 inch smoke shelf, and the flue itself is 12 inches square.

The only time it's ever smoked was about 60 years ago when some idiot (me) tried to burn some almost green American elm in it. That stuff is dang near fireproof, and puts out very little heat -- and a lot of smoke. Live and learn...

The good Count did know about laminar flow, although he didn't call it that, and the principal of the smoke shelf and big flue is that there is laminar flow in there, with the hot smoke rising in the front of the flue and a cooler counter draught coming down the back -- until the whole flue heats up at least.

Mind you it's not as efficient as a modern airtight stove would be. But it is positive heat (and quite a bit of it, with some nice dry ash or hickory or maple or somesuch in there) and it looks wonderful -- and you can even cook in it (there is a crane) if you are so minded.

Your typical modern fireplace will be narrower, and the sides will go straight back -- not angled -- and will often be almost as deep as it is wide. No smoke shelf, or a minimal one, and it just goes up the stack. It's no wonder they don't heat...

MikeAmann

Thanks @captainco for starting this discussion because I made my old burner and boiler more efficient - so much so that now I do have the flue gas condensation problem and now I need a SS liner in my chimney. I have an acid rain storm inside my clay flue liner.
The new SS liner will protect the masonry from further deterioration, but might not completely solve the flue gas condensation problem. I want to understand what is REALLY going on and WHY. I will definitely be following this.

captainco

MikeL_2 said:

     Captainco, 
            I'm not a fan of crazy discussion, but I do appreciate sharing ideas, experiences, processes, successes, documented data, and policies that generate discussion and provide an opportunity for learning. 
             Should I disregard the 7 times rule for combustion venting?

Did you know the seven times rules only applies when two pieces of equipment are common vented. You can have 3,4,5,6,7,8, or more common vented and the seven times rule does not apply.

captainco

MikeAmann said:

Thanks @captainco for starting this discussion because I made my old burner and boiler more efficient - so much so that now I do have the flue gas condensation problem and now I need a SS liner in my chimney. I have an acid rain storm inside my clay flue liner.
The new SS liner will protect the masonry from further deterioration, but might not completely solve the flue gas condensation problem. I want to understand what is REALLY going on and WHY. I will definitely be following this.

If you have flue condensation then the efficiency of your equipment may not be as high as you think. A stainless liner will not corrode as fast as a aluminized steel liner but is does provide a better drain back into the equipment. If you could provide some combustion numbers and some draft readings it would be easy to see why there is condensation. Also we teach to watch the draft after the equipment shuts down to insure you don't have a combustion air problem with oil equipment. Oil equipment can find plenty of air with the burner operating but when the burner stops the draft disappears.

I discuss the thermal conductivity of materials, or their ability to absorb and transfer heat. Tile flues are low on the list. Stainless absorbs more but not as much as aluminum and steel. No venting material cools flue gases down faster than B-vent. Boy does that mess with peoples minds!!

captainco

Great input so far! Thanks!

ScottSecor

@captainco I am perhaps more confused about chimneys and flues than I was before I read your post. Like many on this site, I refer to boiler installation manuals, flue liner charts and code books like NFPA54.

In my area of NJ when we work on a typical older home or building that was built before WWII, we find that many of them were originally heated with coal. Oftentimes, these systems were converted from coal to oil in the 1950's and 1960's. I suspect the chimneys were sized for coal or oil, but I cannot be certain. I also suspect the original boilers had a larger firing rate than the "properly" sized natural draft gas boilers we install today. I also suspect the stack temps (and perhaps flue gas volume) were higher than they are today.

As a result, I suspect many of these chimneys (especially the ones that are partially exposed to outside) struggle to warm up enough to provide adequate draft in all seasons.

We also install commercial cast iron boilers with gas power burners. Sometimes these are forced draft, however most times they are installed with balanced draft. Again, most of the time the chimneys can be difficult to warm up rapidly with the new "properly" sized boilers. Keep in mind that the new equipment might be half the BTU of the original systems.

captainco

I forgot to mention that the National Fuel Gas Code (503.6.9.1) also requires the smallest btu appliance to exit the flue first. That also only applies if you have two appliances. Ever see a 3-story apartment or condo where all the furnaces and water heaters are common vented up one side of the building? Guess where one of the smallest pieces of equipment is located?

captainco

ScottSecor said:

@captainco I am perhaps more confused about chimneys and flues than I was before I read your post. Like many on this site, I refer to boiler installation manuals, flue liner charts and code books like NFPA54.

In my area of NJ when we work on a typical older home or building that was built before WWII, we find that many of them were originally heated with coal. Oftentimes, these systems were converted from coal to oil in the 1950's and 1960's. I suspect the chimneys were sized for coal or oil, but I cannot be certain. I also suspect the original boilers had a larger firing rate than the "properly" sized natural draft gas boilers we install today. I also suspect the stack temps (and perhaps flue gas volume) were higher than they are today.

As a result, I suspect many of these chimneys (especially the ones that are partially exposed to outside) struggle to warm up enough to provide adequate draft in all seasons.

We also install commercial cast iron boilers with gas power burners. Sometimes these are forced draft, however most times they are installed with balanced draft. Again, most of the time the chimneys can be difficult to warm up rapidly with the new "properly" sized boilers. Keep in mind that the new equipment might be half the BTU of the original systems.

I wish I had pictures of some existing flues in older commercial buildings, schools, hospitals etc. You see monstrous flues 100' tall most exposed that worked just fine. Unless you have condensing equipment, flue temperatures are rarely below 300 degrees, which is more than enough temperature to make it out of the flue without condensing. The trick is not allowing the heat of the gases to be absorbed by the flue and cool them down. Flues are not and never will be heat exchangers that need to be heated up.

I know there are so many opinions out there about venting and flue sizing. Unfortunately, they are mostly opinions not factual information. I have never recommended a flue liner to solve a flue condensate problem, but I have certainly recommended they be removed to solve a venting problem.
I know this sounds like heresy or blasphemy but that is why I started this discussion. I get so tired of hearing people say your flue is too big. I have never told my wife she looked to big in her clothes. That is the same thing I tell flues.

MikeAmann

If you could provide some combustion numbers and some draft readings it would be easy to see why there is condensation. Also we teach to watch the draft after the equipment shuts down to insure you don't have a combustion air problem with oil equipment. Oil equipment can find plenty of air with the burner operating but when the burner stops the draft disappears.

We have already been there - done that. Now it's time to make a change - the SS liner.
Then I will have to do the combustion analysis again. Meanwhile, I will learn everything I can about this.

captainco

MikeAmann said:

If you could provide some combustion numbers and some draft readings it would be easy to see why there is condensation. Also we teach to watch the draft after the equipment shuts down to insure you don't have a combustion air problem with oil equipment. Oil equipment can find plenty of air with the burner operating but when the burner stops the draft disappears.

We have already been there - done that. Now it's time to make a change - the SS liner.
Then I will have to do the combustion analysis again. Meanwhile, I learn everything I can about this.



Just mentmake sure the liner you use is at least one size bigger than the equipment flue. After you install it, check the draft in the main flue, above the barometric and watch the draft with just the fuel turned off. If it goes up the liner is restrictive. If the draft stays the same the liner is okay. I am assuming this is an oil boiler?

MikeAmann

Yes, oil-fired boiler.
I was planning to slightly downsize the liner to aid the velocity of the flue gas. My breech connection is 7".
Actually, I won't have much of a choice because my clay tiles are 6 x 10", so the best I can do will be an uninsulated smooth-wall 7" pipe ovalized to 5 x 8.75", and the "insulation" will be the air gap between. I might pour something like vermiculite into that gap. I don't want something cement-like (Thermix), that would make future changes a nightmare. I only want to do this once.
Anyways, the much more efficient burner now uses about 75% less air than it did before to make a hotter, more controlled flame. From that, can I assume that there is much less hot flue gas going into the chimney? If so, then the liner can be downsized.

captainco

You will not increase velocity. Smaller pipe restricts or slows down flow.

MikeAmann

Okay then. Good to know.
So then the ovalized 7" will be the best that I can do.
No, it won't be as good as 7" round, but it will do the job.
I am not having the clay tiles smashed out.

SuperTech

MikeAmann said:

Okay then. Good to know. So then the ovalized 7" will be the best that I can do. No, it won't be as good as 7" round, but it will do the job. I am not having the clay tiles smashed out.

Mike why not have the terracotta removed? If it is already damaged, which in your case is very likely, it's not doing you any favors. With the damaged terracotta removed it will give you more space to install a properly sized and insulated liner. And it will make installing the new liner much easier. 

ChrisJ

SuperTech said:

MikeAmann said:

Okay then. Good to know.
So then the ovalized 7" will be the best that I can do.
No, it won't be as good as 7" round, but it will do the job.
I am not having the clay tiles smashed out.

Mike why not have the terracotta removed? If it is already damaged, which in your case is very likely, it's not doing you any favors. With the damaged terracotta removed it will give you more space to install a properly sized and insulated liner. And it will make installing the new liner much easier. 

I'm going to go out on a limb here and guess that it's because it's far from free and if unnecessary why have it done?

@captainco just said above that flues do not need to be warmed up, so why use an insulated liner?

Bob Harper

Draft is just the pressure differential created by the difference in air densities caused by the hotter flue gases compared to outside. The taller the stack, the faster the velocity. The bigger the flue without restrictions the greater the mass flow.
"The whole mystery, therefore, of curing smoking chimneys, is comprised in this simple direction: find out and remove those local hindrances which forcibly prevent the smoke from following its natural tendency to go up the chimney; or rather, to speak more accurately, which prevent its being forced up the chimney by the pressure of the heavier air of the room." Collected Works of Count Rumford, Volume II, p224. 1795

The smoke shelf on fireplaces was not created to turn downdrafts but merely as a consequence of Rumford narrowing the throat to 4" to create a venturi effect. His interest was in maximizing heat from open hearths. He is considered the father of radiant heat. He also knew too much air flowing up a chimney caused cold drafts across the faces of occupants, which the 18th century mind thought caused illness( colds?). Prof. Peter Rosin conducted fluid dynamic studies in 1928, which disproved the smoke shelf and showed it caused recirculating eddies that restricted and disrupted otherwise laminar flow. Rounding the breast is huge, making it like the leading edge of an airplane wing. Modern sweeps blow out throat dampers and reshape the shelf into a parabolic curve maintaining laminar flow. We use top mounted dampers.
Aluminum absorbs and transfers 3x more heat than stainless steel. Instead of B-vent connectors, use L vent. It's rated for 570F continuous plus a flash fire and is lasts longer.

Bigger flues have increased capacity. This allows great mass flow. The column of warm air acts like a larger hot air balloon thus generating more lift.

Per the IRC Code Commentary, the smaller above the larger appliance input is simply to create greater vent rise off the appliance into the chimney. Low vent rise is a common source of flue gas spillage due to the sudden restriction before sufficient stack velocity has been achieved- about one meter per second per ASHRAE.

The IRC Code Commentary claims the 7x rule is not only to maintain sufficient draft but also minimize condensation. The greater surface area of a flue may absorb sufficient heat to reach dewpoint and condense they figure.

The sizing charts in the IRC were developed by GAMA using empirical calculations. They are based upon interior chimneys.

Why do the sizing charts grant about 30% greater capacity for multiple fan-assisted appliances over natural draft units? Dilution air allowance.

If the flue tiles are damaged or their joints compromised, which accounts for about 90% of them it technically needs a chimney liner. If you change fuels or efficiencies, find damage or defects or are selling it, a Level II inspection is triggered. If it is a flue serving solid fuel, it will need to be sized to the code and insulated to meet UL 1777 for a 2,100F rating at zero clearance to combustibles. Heater liners and listed vents do NOT require cleanouts for gaseous and liquid fuels. If you find flue tile chips or sand in the base of the cleanout, it needs a liner. Do NOT put unlisted galvanized steel connectors cemented into walls. Use ss. Min. 3 screws per joint equidistantly spaced. No seams or screws btw 5-7 O'Clock on horizontal runs. '31 required male-up, which is bad practice. ALL listed venting uses a male-down orientation to contain condensate. Don't forget to support all offsets and every 4 feet of connector. Also observe maximum lateral offsets per diameter and connector wall thicknesses. If you need thicker pipe, use ss for the next effective gauge. In other words, 26 ga. ss = 24 ga. galv.

HTH

captainco

Bob, I thought we would hear from you or I was hoping! What do you believe is the first thing someone should do to make a drafthood appliance vent and not condense?

You know me and down sizing a flue has never been my recommendation and has never been needed to solve a venting problem.

What is your thoughts about the industry standard that it can take up to 20 minutes for equipment to start venting? This is why there is a standard that states CO of 9 ppm is okay in the living space 8 hours a day from vented equipment. Glad these people didn't become doctors because we would all bleed to death!!

Bob Harper

As for condensing for me, I would look at maintaining stack temps above dewpoint such as not under-firing and too much heat transfer (delta T), dilution air from a barometric damper & post-purge. The material used for the vent would rank lower (material influences cooling stack gases) and I'd be more concerned about corrosion and containing/ managing that witches brew.

The term "Steady State" is BS and has done a lot of harm.

Getting up to what I call "cruising altitude" does take a long time. It didn't matter so much when the codes were written, and these concepts born before Ozzie and Harriet when houses leaked like a sieve and energy was cheap. Then came the '73 Oct War when we supported Israel, OPEC cut off our oil> lines at pumps and prices through the roof. In our brilliance, we changed the way houses were built without a care about the consequences. Two major changes noted right off- condensation on the windows and the fireplaces smoking. Now we live in terrariums and have to take all sorts of Rx for all our health issues. It's sad when the air quality standards for a parking garage are stiffer than homes, hotels and offices.

The problem with draft hoods is--they work as designed. They cool stack gases 24/7/365. They add dilution air indiscriminately. Worst, they allow flue gases to relieve or burp into the CAZ. If sustained, we say that 'spillage' becomes a 'backdraft', which has ominous legal overtones. Actually, in the literal sense a backdraft would require a reversal of gravity but that's beside the point. It's a 'flow reversal'. There is still pressure in the stack. Chimneys are stupid and need directional arrows just like those dopey MakeUp Air grilles. They need signs indicating "enter here" and "no exit" on the CAZ side.
Miss you old friend.

ChrisJ

I've yet to see proof that fuel of any kind was ever cheap.
Every time I've looked up fuel costs and then converted them for inflation I've never been able to find anything that ever told me fuel was cheap. Maybe I'm looking up incorrect prices or something, but assuming I'm not and what I've found is accurate.......


Gasoline costs.
1935 - $0.19 a gallon = $3.93 today
1950 - $0.27 a gallon = $3.18 today
1960 - $0.31 / $2.97
1980 - $0.86 / $2.96
1990 - $1.00 / $2.17
2000 $ 1.51 / $2.49

And on and on.
Fuel was never cheap, it's still very similar to the way it's always been and if anything, was actually more expensive in the 1930s - early 50s.

The numbers looked cheap, but they weren't.
I don't think this post is necessarily valid to this thread, but I think it's very valid to the forum. It was never cheap to drive a car, or to heat a building. People just had less stuff to buy. No cable or cellphone bills, no smart phones, tablets etc. I believe cars, trucks and houses were also much cheaper. But fuel was not.

Jamie Hall

You are -- as so often -- absolutely correct, @ChrisJ . Nice analysis. Yes, I was pumping gas on US 66 at $.19 per gallon -- but I was also making $3,000 per year in my day job, and I thought that that was pretty good money!

mattmia2

So is there a book on combustion analysis and venting? I would like to understand it but I am not going to be doing it for a living so I would rather not go to several classes to learn it.

mattmia2

Automotive fuel is something you pay for directly and frequently, you participate in the transaction. Most other things you pay a bill once a month so it is much more visible that you are spending that money even though many other things cost you far more.

captainco

mattmia2 said:

So is there a book on combustion analysis and venting? I would like to understand it but I am not going to be doing it for a living so I would rather not go to several classes to learn it.

The only book on these subjects that are based on 40+ years of field testing are only available in the NCI Combustion and Carbon Monoxide training classes. Because of safety issues and liability we have to make sure this information is not misinterpreted or misused. Because this information pretty much goes against the theories and opinions used in the HVAC industry there is a lot of basics and groundwork that needs to be discussed to understand how this
information was collected and verified. There are students of ours on here.
In the mean time, you just have to keep in touch with this site and the discussions on the subject. There are some very smart people here but when I can help on certain old fallacies I like to comment. When it could be potentially life threatening I will definitely be here!!

JakeCK

ChrisJ said:

I've yet to see proof that fuel of any kind was ever cheap. Every time I've looked up fuel costs and then converted them for inflation I've never been able to find anything that ever told me fuel was cheap. Maybe I'm looking up incorrect prices or something, but assuming I'm not and what I've found is accurate....... Gasoline costs. 1935 - $0.19 a gallon = $3.93 today 1950 - $0.27 a gallon = $3.18 today 1960 - $0.31 / $2.97 1980 - $0.86 / $2.96 1990 - $1.00 / $2.17 2000 $ 1.51 / $2.49 And on and on. Fuel was never cheap, it's still very similar to the way it's always been and if anything, was actually more expensive in the 1930s - early 50s. The numbers looked cheap, but they weren't. I don't think this post is necessarily valid to this thread, but I think it's very valid to the forum. It was never cheap to drive a car, or to heat a building. People just had less stuff to buy. No cable or cellphone bills, no smart phones, tablets etc. I believe cars, trucks and houses were also much cheaper. But fuel was not.

Couldn't agree more.

Between DirecTV, internet, and cell I pay $270 a month. It takes a cold month to get my gas bill to that point. And $4gallon for gas ain't bad either. I remember $4/gallon in 07'. I was making minimum wage and part time hours then and it was like $5 something an hour. My POS ranger got about the same if not worse fuel economy with it's 4 banger then my v8 f150 does today. Lol

Jamie Hall

There is a very fine line between keeping arcane arts within a Guild and letting them be known widely enough to be of benefit...

mattmia2

Someone here might have made a career out of trying to unravel and document that.

MikeL_2

Captainco,
        So you're absolutely certain that the 7 times rule does not apply to orphaned appliances?
          

captainco

MikeL_2 said:

Captainco,
        So you're absolutely certain that the 7 times rule does not apply to orphaned appliances?
          

More than sure - Positive!! Look at a 3 story apartment with 3 furnaces and 3 water heaters common vented. The flue ends up 12 to 14 times bigger than a single water heater. I have seen flues as big as 48" diameters with equipment vented into them with 6" flues working just fine. A flue in nothing but a chase. The bigger it is the easier the flow. I am not recommending oversizing flues, but given a choice slightly bigger is better than almost. But I have never seen making them smaller solve a venting problem. Is 12 ga wire too big for 24 volts? Is a 12" duct too big for 100 cfm? Is a 2" copper pipe too big for 10 gpm? We are not trying to heat the container, just flow through it.

I hope this makes sense to most. I just hate when people spend money on useless repairs.

Again I want this discussion to be helpful and expect to get challenged which is great!

mattmia2

Without actually explaining why. So it was that the code table required the vent to increase after the draft hood, not the liner that fixed the venting issue?

captainco

If one reads the engineering data about drafthoods you will see that equipment with drafthoods are not really connected to the flue, they are just close to one.

"A drafthood isolates the appliance from venting" is how it begins. This is one of the main reasons for venting problems, corrosion and condensation.
Drafthood appliances are designed to keep people warm and clean while they die and yet they are listed as a safety device?

Over 90% of CO poisonings from gas fired furnaces, water heaters and boilers are those with drafthoods performing as designed.

ChrisJ

Is there any chance that's because so many gas appliances use drafthoods?

100% of people that die drink water in one way or another

Is water the cause of the death?

Correlation does not imply causation.

MikeL_2

    Ray Rohlfarth wrote an article that appeared here in August 2015. He describes a scenario that I have witnessed with an orphaned water heater - too large a chimney and condensation attacking terra cotta.

Lance

1) The purpose of a draft hood was what the original name described it as, A DRAFT DIVERTER. Its purpose was to prevent downdrafts from blowing out a pilot, or interfering with the proper combustion of the burners. If the flue did not vent in certain conditions, the burner flame would not make CO in the room.
2) A chimney consists of two main parts, the flue and the building or appliance it is connected to. When installed in a structure that can be enclosed, the buoyancy or draft of the flue becomes dependent on the tight or looseness of the structure.
3) There are 2 reasons we were taught to make sure a chimney worked, A) waste 20% of the combustion heat to create the draft, and A standard brick or tile lined flue, or its connector was not designed to handle acidic condensate.
4) Never trust the new flue liner installer. I have found brand new liners done so bad they actually made the flue worse.
5) Chimney flues next to each other can cause problems and both can lead to death.
6) If we don't know enough, we can't stay safe enough.
7) AS technology advanced into the dark age, many lost sight of the basic laws of physics. no combustion unit between 81% and up should be venting on a flue not designed for condensation. Even when venting, startups cause problems until draft is fully established. Code here I believe states that we must give 5- 6 minutes of non venting before draft is established. We must make it work when all building exhaust fans run, all flues are in function and when infiltration is a minimum.
8) Restaurants are the worst offenders with kitchen exhaust fans.

Motorapido

Jamie Hall said:

There is a very fine line between keeping arcane arts within a Guild and letting them be known widely enough to be of benefit...

There is also only a fine line between a man who is simply standing on the bank of a river and a man who is fishing (Steven Wright jokes always crack me up)

captainco

ChrisJ said:

Is there any chance that's because so many gas appliances use drafthoods?

100% of people that die drink water in one way or another

Is water the cause of the death?

Correlation does not imply causation.

Yes I guess 100% of people that breath air will also die. Not exactly a good analogy.

In 1992 I participated in a field study with AGA Lab on the operation of drafthood equipment in the field. 18 different pieces of equipment with drafthoods were tested in December in Northern Ohio. 18 out of 18 tested unsafe!! Everything was installed according to Code and manufacturers specs. In 1993 they put out a report stating there was a trend in unsafe operation of equipment with drafthoods. However when eliminated all equipment tested safe.

Their engineer was given a gag order and not allowed to test in the field anymore. He had to quit his job and found another one. AGA stopped certifying gas equipment in 1994.

Off the record I was told drafthoods are one of the most dangerous devices ever invented. Their current design has been compromised from the original design. They were created more to eliminate a nuisance than anything to do with safety. Lots of made up stories and opinions. You would be lucky to find a contractor from 1930 to 1970 that did a CO test or combustion test on gas equipment.

Ray is a very smart and talented person. I read much of his information. But as soon as I see someone say a drafthood is a safety device I cringe and realize they got their information from someone that doesn't care if they are endangering life as long as it don't cause them an inconvenience.

ChrisJ

captainco said:

ChrisJ said:

Is there any chance that's because so many gas appliances use drafthoods?

100% of people that die drink water in one way or another

Is water the cause of the death?

Correlation does not imply causation.

Yes I guess 100% of people that breath air will also die. Not exactly a good analogy.

In 1992 I participated in a field study with AGA Lab on the operation of drafthood equipment in the field. 18 different pieces of equipment with drafthoods were tested in December in Northern Ohio. 18 out of 18 tested unsafe!! Everything was installed according to Code and manufacturers specs. In 1993 they put out a report stating there was a trend in unsafe operation of equipment with drafthoods. However when eliminated all equipment tested safe.

Their engineer was given a gag order and not allowed to test in the field anymore. He had to quit his job and found another one. AGA stopped certifying gas equipment in 1994.

Off the record I was told drafthoods are one of the most dangerous devices ever invented. Their current design has been compromised from the original design. They were created more to eliminate a nuisance than anything to do with safety. Lots of made up stories and opinions. You would be lucky to find a contractor from 1930 to 1970 that did a CO test or combustion test on gas equipment.

Ray is a very smart and talented person. I read much of his information. But as soon as I see someone say a drafthood is a safety device I cringe and realize they got their information from someone that doesn't care if they are endangering life as long as it don't cause them an inconvenience.

What is it about the drafthood that causes an appliance to become unsafe?

MikeL_2

        Safety & liability are at the forefront of all of my installs & repairs. Best standard practice & code compliance are my guides, always. 
         There are times when documentation from the reigning authority is needed to settle an issue, usually related to money, property damage, liability, injury, or worse. I'm only a Plumber, how much could I know? So I have to rely on the applicable Mechanical Code as a reference; if it's wrong regarding the language describing the 7 times rule or draft hoods, let's find out what's required to correct it.