Choosing type of chimney liner based on combined burner/boiler efficiency

Gordon_Of_EMass

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I'm about to replace my oil burner with a new gas burner. I have steam heat and a 25-year old boiler, and the exhaust goes up the chimney (all brick, no clay tiles). I understand the importance of getting a chimney liner for gas heat, to avoid CO poisoning. I've read that gas heating with efficiency of 85% or more requires a steel chimney liner (corrosive condensation at low temps), and below 85% a cheaper aluminum liner is ok.

My heating guy says that the new burner is near 90% efficient, but the combined efficiency of the new burner and old boiler is only about 83 or 84 percent. He says that means I can use an aluminum liner instead of steel (and save more than $1,200). That's great news, but need to know that it really make sense to consider the COMBINED burner/boiler efficiency when deciding between an aluminum and steel liner? That is, does the lower efficiency of the boiler really make the flue exhaust hotter than otherwise?</span>

Tim McElwain

If I am hearing you correctly

you are converting an oil design boiler over to gas using a gas conversion burner, is that correct? If so you should follow the recommendation of the burner manufacturer for venting and chimney lining.



The concern with venting today is lower flue gas temperatures dues to less heat going up the chimney. That creates a possibility of condensing in the flue or chimney.



I do not know of any gas conversion burners that give 90% efficiency. The typical combustion efficiency with most gas conversion burners is about 80% to maybe 82%. That does not present any real condensation issues most of the time depending on the height of the flue and how far the equipment is from the flue.



Make sure that the installer does a combustion test with an electronic combustion analyzer. If they do not offer that then get a different installer who does.

Mark Eatherton

Casual observations from the field regarding aluminum flue pipe liners...

EVERY gas fired appliance is a condensing appliance when first started. Aluminum and condensation do NOT like each other.



I read the Selkirk I&O manual, and they require an annual inspection of the liner to insure integrity and warranty.



I had the opportunity a while back to look a an installation that was done here in Denver using a CFT boiler, operating with baseboard, which is typically NOT a condensing situation. What I found caused the hair to stand up on the back of my neck. The aluminum flue liner (approximately 10 years old) was COMPLETELY gone. All that remained was the wire that was originally a part of the liner. A lot of chimney debris (soft red brick typical here in Denver) had accumulated at the base of the chimney, and had nearly blocked off what was left of the flue gas passage way.



Fortunately, we completely replaced the whole shebang with a condensing appliance and ran new plastic pipe, but it makes me wonder how many contractors are actually following the liner manufacturers recommendation for annual inspections after the fact...



I know personally, I've never done so, and no longer work for the company that use to install them, as required by code. And knowing how things work at the previous employer, I can just about guarantee that annual liner inspections are non existent.



Makes me wonder if aluminum liners are really worth it, or if one would be better of using a heavier gauge of steel of stainless steel to reline masonry chimneys...



Proceed with caution.



ME

Gordon_Of_EMass

Gas burner

It's a Carlin EZ-Gas Power Gas Burner.  It can optionally convert from propane, but I will be using it to burn natural gas from a new gas line installed by the utility company.  The aluminum liner I'm considering has a 5-year warranty, but it only applies for 85% max efficiency.  The burner specs I have seen do not give the efficiency (maybe because that depends on the boiler).   

Mark Eatherton

Burner efficiency is important, but...

it is only the first step in overall efficiency, and if it is misapplied (under or oversized) it WILL affect the overall efficiency of the equipment.



If the burner is not efficient, nothing else down stream (heat exchanger, distribution system, controls) will matter. Even if the burner is 100% efficient (theoretically possible, rarely ever seen) at converting a given fuel to thermal energy, if everything else down stream is messed up, your net efficiency will be low.



The higher the mass of the system (boiler and emitters) the greater the potential for short and long term condensation production, and the possibility of degradation of aluminum liners. If you have to replace the liner every 5 to 7 years, it is going to be an expensive ongoing proposition.



ME

Tim McElwain

As someone who has installed

over 3,500 conversion burners it is very unlikely that your installation will rot out the liner. I have several jobs which have been going for over 15 years without rotting. They are inspected every year by myself or a company who has taken over some of my customers and were trained by myself. If you are concerned then go with the more durable liner. I do not know exactly what conditions exist in your installation so it is difficult to make a determination as to the aluminum liner being adequate.



Check with Carlin as to what they would like to see for a flue liner with their burner and they also have an application manual which will probably list your boiler and what efficiency can be expected when using the EZ burner. They will in fact ship you a burner all set up just for your boiler and if a heat loss or radiation survey was done and it is made available to them they will match everything up. Then the burner will need some fine tuning hopefully by a trained gas conversion burner expert who has been trained in the installation of such burners. All new flue pipe connector and a double swing barometric with a spill switch will be required. A final combustion test will need to be done with a electronic combustion analyzer.

Steamhead

Do NOT use an aluminum liner

under ANY circumstances.



Since your chimney has been used for an oil burner, no matter how well it's cleaned there will still be some residue in there, which will eat up the aluminum liner. Our chimney contractor will not install aluminum in any such flue, and does not recommend it for a flue that has only been used with gas. If your chimney contractor is pushing aluminum, find a different chimney contractor.



Stainless is the only way to go. Sure it costs more, but it will last. We specify it on all our jobs. This is NOT the place to cheap out.



ME, did the chimney you referenced once serve an oil burner?

Mark Eatherton

No oil...

There is a possibility that it was coal fired early in its life (over 100 years old) but never oil To my knowledge, there are only a hand full of oil burners here in Colorado. Most of them were installed by East Coasters who didn't know that propane even exists.



ME

Tim McElwain

Are we all talking

about the same thing here. Chimney liners up here in the New England area are very diverse. There are liners specifically used for natural gas and propane only. There is type "B" vent gas only. Then we have heavy duty class L liners and then stainless steel. Also the word unlined means it is typically a brick and mortar inside. However in some jurisdictions a clay tile liner is classified as unlined due to its poor conductivity.



In the past you could not use Type "B" vent with conversion burners as there was concern over high temperatures affecting the max temp on B vent of 550 Degrees. Some of the conversion burner companies now say you can.



I have not experienced what "Steamhead" s addressing here as it has always been a requirement when installing conversion burners and today all chimney installs have to be pre inspected. If the chimney showed signs of saturation due to any residuals it had to be cleaned and reinspected. Then and only then was a liner installed.



I have experienced even with clay tile liners in chimneys a large collection of what is called fly ash accumulating from the clean out up to the first breach into the chimney one year later. That established a required inspection after one year of all conversion burner chimneys.



The liners I have seen here in New England are not aluminum to the best of my knowledge but a heavy alloy flexible material designed for use with gas and oil. I am not sure if they have any aluminum.



If by aluminum this poster is talking about something to the consistency of a dryer vent then absolutely not.



I guess I am just not seeing this aluminum stuff up here in NE that Steam head is talking about?

Steamhead

If it was coal

it probably left some similar corrosive residue. Not unlike cinders, a by-product of coal burning, which I seem to recall they don't want you burying stuff in.



Tim, you might be right. Not sure what's required in your area, but around here anything goes.

Gordon_Of_EMass

Some more info

Thanks for all the comments, they're all helpful.

I'll check with Carlin about what liner they recommend to go with the heater/boiler combination. My heating guy did his own checking (when he said aluminum is ok given the 83%-84% efficiency), but I don't know if he checked with Carlin, so I'll make sure. The chimney guy told me about the 85% max efficiency for using aluminum, and that the liner will disintegrate if the efficiency is too high.

About combined heater/boiler efficiency: Although it would be great to get 90%-100% efficiency, in this case the burner/boiler combination will yield (according to the heating guy) 83%-84% efficiency, and he recommends not replacing the boiler because a newer more efficient boiler wouldn't be worth the expense at the rate I use energy (I keep my house cool in winter -- I spent only $1,000 on oil last year at peak prices), and the current boiler is doing fine.

Since I've decided to go with this new gas heater (with gas input, no conversion needed) and keep the old boiler, my only concern now is that the efficiency could actually be too high for an aluminum liner. And I don't know if the lower boiler efficiency really means that the flue exhaust will be that much hotter (allowing less condensation), or does the lost heat from the boiler just go somewhere else (like my basement), instead of heating the flue exhaust?

It sounds like cleaning the chimney is important before chimney liner installation, but I don't quite understand why, since the exhaust flows inside the liner, not outside next to the chimney surface. Is it because there's condensation on the outside surface of the liner, and it absorbs acidic residue from the chimney surface (from past oil burning), even if the liner/chimney surfaces aren't touching?

My house is about 100 years old. I don't know if it ever used coal, probably just oil.

Charlie from wmass

Why waste your money on the cheaper product

I often get hired by people who can not afford to do the job twice. I am not the low bidder but I get paid, the job works properly, and I go to the next job. I strongly suggest going stainless unless you like paying the chimney guy twice. The liner falls under supervision of the licensed installer of the gas equipment in MA. They do not have to pull the liner but two permits and inspections need to be pulled for them. One from the mechanical / building inspector and one by the gas inspector.

Charlie from wmass

Also note with conversion burners

If the burner is burning at the same btu input rating as the oil burner had the efficiency rating is 2 to 4 less than the oil was getting in my experience. If you can down fire and still meet your required load you can get decent numbers from a conversion burner, 90% or even an actual 85% I would very much doubt though.

Gordon_Of_EMass

Buring gas, not converting from oil

Just to clarify this, I'll be using the Carlin burner as a natural gas burner, not a conversion burner with oil.

VictoriaEnergy

If....

A stainless liner is generally considered better than aluminum, but aluminum liners have a good track record under the right conditions.

I'd say IF the chimney is in good condition; AND IF it is in the center of the house; AND if the boiler will have a draft hood; then an aluminum liner will work fine.

Draft hoods tend to draw in extra dilution air that will lower the dew point of the exhaust and help keep the liner dry.  Not as efficient though.

If the condition of the chimney, especially the mortar capping and pointing between the bricks is in good shape, the chimney won't absorb much moisture and the soot residue from previous fuels won't be an issue.

If the Chimney is on an outside wall, it'll run colder and have more condensation issues, more likelihood of moisture activating corrosive residues in the chimney, so a stainless liner will be more durable.

If you have to retrofit a stainless liner because the chimney is on an exterior wall, maybe the money would be better put towards a side wall vented higher efficiency boiler. 

Charlie from wmass

A natural gas burner on an oil boiler

is a conversion burner.

Gordon_Of_EMass

Conversion boiler

Charlie, thanks for helping me with the terminology on "conversion boiler", now I get it.



My boiler is a (roughly) 25-year old Pensotti, model #R1-4S.  I talked to someone at Pensotti, and he estimated I'll get 83-84% efficiency.  The lower efficiency means the exhaust will be that much hotter (so less condensation).  The chimney is in the center of the house, but the boiler has no draft hood.  All things considered, given the acidic residue on the chimney surface from oil burning (even after the sweep cleans it), I guess an aluminum liner could wear out after a decade or two, so I'll probably go with a stainless steel liner instead.