Boiler carpet--one more time

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Old 01-10-07, 07:38 PM
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Smile Boiler carpet--one more time

Figure since a few more pros are here then when I first asked this question, I'll try again. My Biasi B10-4 was shipped without a combustion pad. QHT started supplying the blankets again after not shipping the boilers with for a while.

What purpose does the carpet serve in a cold start wet bottom 2-pass boiler? Does it improve the combustion, reducing sooting on the base? Will it help raise the stack temp a bit if it's on the marginally low side for a tile chimney flue? Does it affect the burner combustion if installed (requiring a tech to readjust the burner?) I picked up a trim kit for the Biasi, and will have a cera-pad available if it's worthwhile using one.


Pete
 
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Old 01-10-07, 08:47 PM
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If by "carpet", "blanket" and "pad" you are referring to a refractory material such as Kaowool or a spun ceramic fiber, then what it does is allow for a higher firebox temperature more quickly upon burner ignition.

I am not familiar with residential sized boilers and so take this info for what it is worth to you. If you have an oil-fired boiler with a minimal amount of water then you are quite likely firing the boiler for short, but frequent periods. The ceramic liner on the bottom of the combustion chamber will heat rapidly (matter of seconds probably) and improve the oil combustion. It will also, to some degree, insulate the bottom of your boiler allowing for a greater differential temperature between the water outlet and return temperatures, normally (within reason) a good thing.

If this boiler has a power gas burner then it is similar to the oil burner described but of less importance to combustion. If the boiler has an atmospheric gas burner then there will be little, if any, improvement in combustion efficiency.

It may somewhat reduce firebox sooting, it will have little or no effect upon the exit gas temperature and will probably affect the overall combustion efficiency and require re-tuning of the burner, especially if it significantly changes the volume or shape of the combustion chamber.
 
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Old 01-13-07, 05:35 PM
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Furd

Hi, thanks for the reply! Yes, the "cera pad" is the product name of the material supplied by Biasi, and it sure looks and feels just like a sheet of 1/4" Kaowool. I showed a photo of the sooting on another forum, and someone suggested putting a "carpet" in the boiler, I think combustion pad is the correct term. It's a 12" x 12" sheet, nothing special. The only thing I'm not sure of if it should be cemented to the floor or if it just lays there. Nothing in the manual regarding how its installed.

Pete
 
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Old 01-13-07, 06:04 PM
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Thumbs up Furd knows his stuff! Another factor possibly.

For a few seconds after firing, if a boiler is cold enough, the combustion gasses will often condense inside the combustion chamber, then after a few more seconds, it will evaporate causing fluxuations in pressure inside the combustion chamber. This may or may not be a factor. If the manufacturer sent you a free pad, then they must have figured out that it runs better with it. As far as installing the pad, if it just sits on the bottom, then it should be ok, but if it goes up the sides, you may want to use a product called 'waterglass' to adhere it (use nitrile or latex gloves when handling it, and clean the surface that it is to be adhered to). Read the directions that come with it, and be careful not to spill it on anything else. It sticks really good after it dries.
 
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Old 01-13-07, 06:38 PM
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combustion pad

Actually, I found out they had started sending the pads out with the boilers from another forum. I bought a complete trim kit to get the pad on a well known auction site. Seems a bit extreme, but for nine bucks I got the pad, spare 4006A aquastat, T&P indicator, boiler valve, pressure relief, and a bunch of other goodies. I have water glass.. I install the pad before I call my oil tech to service the burner in the spring.

Pete
 
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Old 01-13-07, 06:49 PM
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Thumbs up 9 bucks, huh?

Sounds like a good deal! I've gotten some really good deals on online auctions too. (my name there is HVAC-EMT too!)
 
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