Chimney restore: Stainless liner versus Heatshield ceramic refractory coating

Motorapido

10 year old Peerless gas boiler vented into 100-year-old clay-tile lined chimney. Clay tiles intact. Some aging degradation of mortar between tile liners. Chimney sweeps from two companies have recommended either stainless liner or ceramic refractory coating. I also got a quote to bypass the chimney and vent the boiler out through the foundation wall. I don't like the idea of busting through my brick foundation and I don't like the idea of adding another control mechanism to the boiler that could fail and leave me without heat, and I don't like the idea of a potentially loud fan.
Some chimney people are big advocates of the ceramic refractory coating, if the clay tiles, like mine, are in pretty good shape. I read arguments about the durability of coating versus stainless, with some saying that stainless liners can go bad in 10 years and the coating liners should be good for 20 or even for many more years than that. The Heatshield coating system is applied with a wedge shaped bell that is pulled up the chimney as the mortar is poured from the top, with the rising bell smearing the coating onto the clay tiles. I am told the labor to install is less than doing a stainless liner.
Opinions please. What system would you go for, and why? I am always willing to spend more to get better quality and extra longevity. At age 57, I hope to never move from the house, so if the COVID doesn't cut me down early, I hope to live here another 40 years. Longevity and quality are important to me in whatever I choose. Thoughts?

ethicalpaul

I can't see how the labor and especially not the other costs could possibly be less than dropping a SS liner down the chimney!

Did you get a price for the whole job? You can't quote it here, but it must be multiples higher than a liner I would think.

Were the "some" saying that SS rots out in 10 years possibly the coating companies?

Motorapido

The chimney guy said it takes only about two hours to do the refractory cement application. They drop the applicator down the, pour in the ceramic refractory mortar mixture, pull the applicator back up to the top, clean up a little slop and they are done. They do more stainless liners than this technique since people in the USA are not as familiar with it and ask for stainless. My reading tells me it has been the most common approach in Europe for decades. They said they often encounter fiddly issues installing stainless liners due to internal irregularities in the chimney and clearance issues. I will be getting a price quote in a week or two after they complete the crown cover job they are currently scheduling for me.

Bob Harper

The acid etch prep takes about 1-2 hrs. then it has to dry. HS takes about a day. We do it all the time for fireplaces. You want ss for heater liners. 10yrs? most carry a lifetime or never expiring warranty. Aluminum rarely lasts 10 yrs. but not ss. You're getting some bad info. In Europe they use the German system, Ahrens, which is a vibrating bell pulled up through a zero slump mix 1.5" thick then a gel coat or English system using an inflated bladder with a slurry 0.75-1" for a 2100 deg. rated liner listed for zero clearance. HS carries a 20yr. warranty. Where are you located?

Motorapido

Thanks, Bob. So you prefer a coating system like Heat Shield for fireplace flues, but prefer stainless for gas boiler flues? For some reason, I would have guessed the opposite. Seems like the exhaust from a gas boiler is clean, except for the acid formed in condensing exhaust from the gas combustion. The fireplace would still build creosote and need to be swept, and I was assuming that the creosote sweeping process on the fireplace flue might tend to abrade and degrade a coating system like Heat Shield. I've read that it is more expensive to do a stainless liner for a fireplace flue than for a boiler flue, because of greater complexities of attaching the liner at the damper/firebox side of the fireplace. My issue on the boiler flue is that I need an 8 inch liner, and the two chimney companies that have looked at it say that it would be very tight to drop an 8 inch stainless liner into the boiler flue, and they would need to ovalize the liner, which didn't sound too good to me. I want to select the best and most durable approach and spend what it takes to do it right. But I also don't want to just throw money at it, if a lesser-expense approach is as good or nearly as good.

Motorapido

Bob Harper said:

The acid etch prep takes about 1-2 hrs. then it has to dry. HS takes about a day. We do it all the time for fireplaces. You want ss for heater liners. 10yrs? most carry a lifetime or never expiring warranty. Aluminum rarely lasts 10 yrs. but not ss. You're getting some bad info. In Europe they use the German system, Ahrens, which is a vibrating bell pulled up through a zero slump mix 1.5" thick then a gel coat or English system using an inflated bladder with a slurry 0.75-1" for a 2100 deg. rated liner listed for zero clearance. HS carries a 20yr. warranty. Where are you located?

In in Harrisburg Pennsylvania. The capital of the entire northeast. 😃

ethicalpaul

Motorapido said:

The chimney guy said it takes only about two hours to do the refractory cement application. They drop the applicator down the, pour in the ceramic refractory mortar mixture, pull the applicator back up to the top, clean up a little slop and they are done. They do more stainless liners than this technique since people in the USA are not as familiar with it and ask for stainless. My reading tells me it has been the most common approach in Europe for decades. They said they often encounter fiddly issues installing stainless liners due to internal irregularities in the chimney and clearance issues. I will be getting a price quote in a week or two after they complete the crown cover job they are currently scheduling for me.

That's good information, but I have to wonder...if a chimney is fiddly with clearance issues to run a flexible pipe through it, how fiddly is it to lower and raise a wedge shaped bell?

STEVEusaPA

They're not going to lose their bell. Much like a cat with their whiskers, they have a feel for what can fit. Not saying it's never happened.

Bob Harper

I prefer stainless steel over Heat Shield or any similar joint repair if the client will pay for it. You have to match the alloy to the application. 304L ss for woodburning, 316L or 316Ti for coal, oil or CAT I gas. AL294c for CAT III or IV gas or similar super ferritics. If the chimney is rotten with more than 25% of the mortar missing, it should be restored with a cast in place liner system such as Guardian. Joint repairs are always a stop gap measure (pardon my pun). Some jurisdiction don't allow them.
The bell is very heavy duty pulled by a heavy cable to a special winch made to mount at the top of the chimney. It ain't breaking. Pulling ss liners through offsets and constrictions can cause the pulling cone to pull off, which is always fun.
FYI, clay tile wasn't available until around the late 1920's. It was retrofitted by lowering sections down with the bottom edge buttered with OPC mortar. This is not a currently recognized relining method as there is no control over tile alignment, control of the joint thickness or striking the joint inside and out. The old Ordinary Portland Cement-based mortar does not hold up and will fail. NFPA 211 calls for a medium duty non-water soluble calcium aluminate refractory cement mixture. Yeah.
You're a little too far from me to help- outside Philly.

motoguy128

I’d go SS liner. The aluminum liners only last maybe 10 years. SS should last 20-30 unless you have excessive condensation in your flue gases or a short cycling boiler. Might be shorter life if you run it in summer for DHW.

The coating.... here;’s my concern. When that coating fails and starts breaking off, then what? You can’t remove it. You now have to hope a SS liner still fits... and you are back to where you were. What if they apply it wrong and it fails in suck a way it mostly blocks to flue. (Not likely, but possible). Realistically, I suspect hte coating eventually cracks and is no longer fully effective. Unless it’s epoxy, not cement based, it will likely not flex the same as the existing brick and clay tiles. I’d expect cracks the same was foundation And stucco coatings crack when applied to stone.

jumper

Are these chimney problems due to efficient boilers whose exhaust is too cool?

Motorapido

Bob Harper said:

You're a little too far from me to help- outside Philly.

Hey, if you change your mind and want to quote the job, I would welcome a fellow Heating Help participant to do my chimney lining. Harrisburg is an easy drive from Philadelphia.
Thanks for the info you provided. One thing I didn't mention is that my boiler is about 60% oversized and it does short cycle, which I assume results in more condensation in the chimney. I have the automated flue damper operating. In a way, I guess that probably makes the condensation in the chimney worse, since the post-fire boiler heat stays out of the chimney between cycles, allowing the chimney to cool more than if the damper was open all the time and allowing waste heat to continue to flow up the chimney.