Replies

1. 
   Bob_Walker | May 11, 2001 03:36pm | #1

   *
   Er, "Cap ruins the look of the chimney and interferes with its draw."???

   How do you know that the cap is interfering with its draw?

   They
   i probably
   installed a metal liner all the way up the old chimney flue (often needed whan an 80+ furnace is vented into an older flue designed for a lower efficiency "naturally drafted" furnace.)

   You aren't by any chance trying to use that old flue for someting else? If so, "No No, bad dog!"

   "Wouldn't chimney tiles do just as well?"

   Not sure what you mean by "chimney tiles" but the answer is probably "NO!"

   Please keep in mind that chimneys and flues are supposed to remove potentially deadly gases (e.g., carbon monoxide) from the house. Screw 'em up and you can kill or maim people.

   Assuming (as above) that a new metal flue was run all the way up the old flue, if you take the cap off, you could get rain water running down into your furnace. You don't want that.

   Regarding how it looks: quick, withour looking outside, how many houses in your neighborhood have those metal caps on their chimneys?
   You're only seeing it on your house because you're thinking about it right now, no one else will ever give it a thought (except some weirdo like an HVAC contractor or home inspector or chimney mason, and they will see the inner, classical beauty of the the system, not the surface, romantic "ugliness.")

1. 
   Harriet_Hodges | May 12, 2001 03:17am | #2

   *Sigh. This isn't the answer I wanted. Yes, I use the chimney for the fireplace--which drew better before the metal liner went in. The cap is plug-ugly, whether the neighbors like it or not. It offends me every time I drive in. (Eighty percent of a house's charm is in its roof.) But thank you for attempting to set me straight.

1. 
   Bob_Walker | May 12, 2001 03:36am | #3

   *Hmmm,Something weird here. The fireplace and furnace should have been on separate flues in the chimney (assuming its a word burning fireplace), so, if they did run a flue liner it should be on another flue than the fireplace's.Is the flue cap on a separate flue from the fireplace? Has the fireplace draft become worse since the new furnace and metal cap were installed?If this is the case, i maybethe draft can be improved by adding an extension. Check with your HVAC guy or a chimney sweep."(Eighty percent of a house's charm is in its roof.)" Agreed, but I think its probably exagerated in your mind right now, and the pain will fade.

1. 
   Harriet_Hodges | May 12, 2001 03:42pm | #4

   *Thnks, Bob, I'm embarrassed I haven't done my homework. And I didn't frame my question properly, either. (I do know there should be two flues. )This is a house I will sell. But on the one I build, surely it is possible to make a brick flue--with a cap, I suppose--function for the gas furnace? How is it handled in a new house so that glittering cheap metal cap doesn't ruin a beautiful masonry chimney? And doesn't metal corrode pretty soon (say, 30 years) even if it is stainless? I know it does with high-efficiency furnances.Thank you for your time. I am the indexer for the magazine, but I've never seen this question addressed--except in the warning about high-efficiency gas furnaces.

1. 
   Bob_Walker | May 13, 2001 03:08am | #5

   *Harriet,"How is it handled in a new house so that glittering cheap metal cap doesn't ruin a beautiful masonry chimney?"In my neck of the woods (NW OH) in new construction either (i) the 80+ furnace is vented with B-vent up to a rear, non-conspicuous roof plane or (ii) a 90+ furnace is insatlled with the plastic flue being run inconspicuously through a side wall a couple of feet above grade.In existing construction, the metal flue is usually run up the chimney as its the only available chase to above the roof plane.[Of course, in my neck of the woods there aren't many good looking, tasteful homes being built (e.g., i very fewmasonry chimneys.)

2. 
   Mike_Smith | May 13, 2001 11:56am | #6

   *harriet .. in a real high end house ... all chimneys will be masonry.. and all flues will be clay flue liners..if there is specialty equipment that requires a specific flue it will also be designed into the masonry structure...the reason the metal flues are used so often is "time and money"... but ALMOST anything that can be vented in metal can be vented just as well in masonry..some configurations require a lot more creative detailing than others.. again... time and money..

3. 
   Bob_Walker | May 13, 2001 12:59pm | #7

   *Mike, good point; I mustof been having a senior moment. I i thinkthe trick will be sizing the flue prpoerly for the furnace output and rise (and location of the chimney.)If I understand the issue, the primary concern is maintaining proper/sufficient flue gas temp so that you don't get major condensation inside the flue.I doubt if you could vent 90+ thru masonry, but don't know for sure.A question I haven't been able to find an answer for is whether 90+ natural gas furnaces (and boilers) should have the acid neutralizers that 90+ fuel oil boilers need. Any idea?Bob

4. 
   Harriet_Hodges | May 14, 2001 02:38am | #8

   *Ah, great, Mike and Bob. You're dealing with the root questions that I'd like to see answered. I know the acids are highly corrosive--but wouldn't metal always "corrode" (degrade) more quickly than flue liner or brick?

5. 
   Mike_Smith | May 14, 2001 03:41am | #9

   *harriet.. i was speaking in generalities...some equip. has UL ( or equiv. ) approval based on certain components..some mfrs. like Metalbestos , have SS components..some of these can be installed in masonry to disguise the fact they are metal..each piece of combustion equip. will have to be treated on a case by case basis...and it all has to conform to the mfr's specs.. and local codes..

6. 
   Harriet_Hodges | May 14, 2001 03:46am | #10

   *Thanks, Mike. I don't want to run this into the ground--but answer me this: is it not true that if time and money were irrelevant that masonry would always be preferable? Is there any gas from any fuel that is better handled with metal?

7. 
   Mike_Smith | May 14, 2001 05:15am | #11

   *for the most part... masonry rules...BUT... some of the sealed combustion units... and some of the power vents have very particular venting / flue requirements.... equipment specific...

8. 
   Bob_Walker | May 15, 2001 01:06am | #12

   *Harriet,I'm going to see if I can get a heating guy I've met on the interney to jump in here, he'll bring some good info if I can lure him over.

9. 
   Gary_Reecher | May 15, 2001 03:07am | #13

   *Bob,I think this is the forum you wanted to me to look at? Harriet,Venting of new gas high efficieny furnaces and gas appliances must follow the requirements outlined in the National Fuel Gas code NFPA 54-1999; and manufacturers installation instructions. Which most manufacturers refer to for the venting of their 80 percent efficiency furnaces. The manufacturers instructions for venting 90 percent efficiency furnaces are listed in their installation manual. A lot of thought has gone into the compilation of NFPA 54-1999 to provide best efficiency and equipment safety. Venting into clay tiled liners is permitted if the sizing of the liner meets the code. Unfortunately as the equipment efficiencies increased this meant that the available amount of btu's that were being used to properly heat brick and tile liner chimnies decreased. Example a furnace with a 50 percent efficiency that had a gas input of 140,000 btu's per hour. Half of the input btu's were being used to heat the chimney 70,000 and the other 70,000 was transferred to the house. Through insulating and window replacement your house now only needs 45,000 btu's per hour. A 60,000 btu 80 percent efficiency furnace will do the job with a spare 3,000. Now instead of 70,000 btu's to heat a tile lined or brick chimney you only have 12,000 btu's. Besides having less volume the temperature of the flue gas is much lower. Following the charts in the code your existing chimney is too large to properly vent. Several things can happen. The moisture in the flue gas is driven into the brick and tile. The temperature is lower and the moisture is never cooked out. When the furnace cycles off the moisture in the brick at the top freezes. The next furnace cycle the moisture is thawed and is driven deeper into the brick. This process continues as mortar is broken loose, bits of brick and sometimes whole bricks come loose until the bottom of the chimney is filled with debris and venting is restricted or stopped. Because flue gas temperatures are lower it is possible for an ice dam to form within the chimney on frigid days when the temperatures drop into the negatives. The other aspect of venting into a chimney that is not resized is loss of efficency. An article in a trade journal "Fuel Oil News" had an article unlined chimnies reducing the efficiency of a new furnace by as much as 50 percent.Granted metal chimneys sticking out of brick ones may not be pictureque, but proper sizing is important. Talk with your contractor about the possibility of painting the metal pipe to make it blend in with the chimney.

10. 
    Bob_Walker | May 15, 2001 03:22pm | #14

    *Thanks, Gary.FWIW, gary maintains an excellent HVAC site, and has a comprehensive set of links for carbon monoxide at http://www.essex1.com/people/mechacc/carbon%20monoxide%20links.htmA related question for Gary:Sometimes in cold weather I will see condenstation in the top foot or so of a clay flue liner.At what point should I mention this condensation as a long term concern? E.g., temp above 20 degrees; or obvious dripping back down the flue liner; any visible spalling of the flue liner; or any condensation should be further investigated; or ...?(I haven't made note whether this is most like to occur when an 80+ has been installed without a metal flue liner, but suspect that's the case.)

11. 
    Gary_Reecher | May 16, 2001 04:48am | #15

    *Robert, If you see staining coming out of a chimney breech or vent pipe then the chimney is condensing and should be resized with a liner.

2. 
   Harriet_Hodges | May 16, 2001 04:48am | #16

   *
   How about removing the ugly metal cap that installer of new gas furnace (not "high-efficiency") said was required? Wouldn't chimney tiles do just as well? Cap ruins the look of the chimney and interferes with its draw.