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Specific Flue Question

09/19/2008 4:56 AM

Will insulating the exposed section of flue liner (see pic) improve updraught?
( Please don't say 'get a new boiler' or 'call in a qualified blah blah...' etc)

Grumpy Del

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#1

Re: Specific Flue Question

09/19/2008 8:21 AM

I would think so! All the heat radiated out of there is not going up the flue and as it's ripply metal it will dissipate the heat better out of the flue like a heat sink! You want the heat inside to cause the updraught If you are going to lag it, make sure you use the correct lagging! You don't want a fire or melted insulation in that snuggly little cat den of yours do you!

Anyway Del, why so grumpy? Has Mrs Cat been on the nag because of the weird smell again? Get her some flowers

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#2

Re: Specific Flue Question

09/19/2008 9:08 PM

Of course it will--on Earth at least.

MM

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#3

Re: Specific Flue Question

09/19/2008 10:54 PM

Insulating will lower the temperature gradient as you go up the flue. and you will have a longer column of higher average temperature, so your flue gasses will enter free air at a higher temperature.

This will increase the draft. It will also waste more heat.

Often a small input fan can be used for the flue to cause enough draft. That way you can extract all the heat you can independently of the need for density to drive the gasses out of the building.

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#4

Re: Specific Flue Question

09/19/2008 11:08 PM

Good point

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#5

Re: Specific Flue Question

09/20/2008 2:32 AM

Thanks for the answers guys.

I finally managed to find relavant regulations for flues, including smoke testing etc... (Building Regs Part J blah blah) Interestingly it gives some guidelines and recomendations, but also says that much of it is down to observation, experience and local wind condidtions.
In otherwords some bloke with a CORGI certificate isn't necessarilly giong to be any better off than me...as I have a good understanding of the pressure gradient across the building. (The wind whistles through the garage which runs right through, front to back....maybe I could install a wind generator there?)

I think the problem is actually a 'start up' problem when the flue is cold, and of course, this time of year the boiler is only comoing on in short bursts which is exacerbating the problem.

I shall start by insualating that section as it's a cheap quick and easy try out (also 3foot isn't such a distance to fall as off the roof)

Del

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#6

Re: Specific Flue Question

09/20/2008 2:54 AM

Hello Del the cat, You need to check to see if the flue liner is the "duel type".

that is it has an inner liner that the exhaust gas that goes up and out, and fresh air comes down from the outside to the boiler. The outer shell stays cool with this type of liner and does not need any insulation.

If the liner is just exhaust only you need to be careful about NOT causing the upper portion that goes through the roof from getting to hot. That could make the cat house

a hot place indeed! And by changing the flue temperature it could compromise the design and clearances needed and integrative of the flue.

Why do you think you need better updraft? Are you getting carbon monoxide or smoke inside? Have you done any sealing of the house (made it more air tight)? is the boiler having burner problems like incomplete burning? Or a fresh air inlet pipe could be blocked that comes from a different area. Or are you just trying to make it a little more effect?

hope this gives helps

metalSmith's

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#7
In reply to #6

Re: Specific Flue Question

09/20/2008 3:07 AM

It's a single flue liner.
I know 'cos I fitted it myself a couple of years back when I re-furbished the boiler and fitted it properly !...It had been installed about 6" away from the back wall with a bend in the flue and it was sticking out into the room. So I tidied it all up prior to re-fitting the kitchen and adding my DIY solar hot water panels!

I have another thread on the subject with more info, but it was drifting off onto non-specifics.

Basically, it's safe enough but smells a little at start up in certain weather conditions.
So I'm trying to give it a bit more updraught in the most cost/labour effective way.
(IT still smells a bit even if I open doors windows etc....so I'ts not a lack of ventilation, more a lack of draw.)

Del

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#8
In reply to #7

Re: Specific Flue Question

09/20/2008 4:44 AM

Hello Del, How much flue is above the roof line? Maybe a little higher hight may help.

By having the top up in "clear air" and not in the shadow of the roof line may help.

Or you may be able to find a draft control to put in the flue above the boiler. What I have seen here in wood stoves is a "T" looking section with a baffle on the end that opens and closes to control the introduction of air. "Not quit sure how to use it or if it's self regulating"

These are about all I know to try or suggest.

Good luck

metalSmith's

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#9
In reply to #7

Re: Specific Flue Question

09/20/2008 5:51 AM

@ start-up only sounds like the inertia of the contents of the flue resisists (momentarily) the entry of tht hot exhaust that does induce the draught.

Is some form of 'soft start' possible?

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#10
In reply to #7

Re: Specific Flue Question

09/20/2008 6:18 AM

the older models have efficicncies in the 60% range. New condensing ones are 98%.

Take your annual fuel cost and calculate the saving at current gas prices, then recalculate with gas going up 10% annually.. It might cost $3000 to install a new condensing furnace, you can do the math.

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#11
In reply to #10

Re: Specific Flue Question

09/20/2008 7:20 AM

Have to factor in the effort involved of fitting it and a new flue, and the environmental cost of throwing away a perfectly servicable boiler.
The payback would probably be 5 or 6 years.
A new one wouldn't last as long as the old one...the old cast iron heat exchanger isn't going to burn out/fur up/pin hole etc.
The CORGI fitter who lives down the road was telling me that he has an old model like mine and said they are much more reliable than the new ones.
So if I figure the new one would wear out in 5 years, I'll wait 5years, by then the reliability will have improved or maybe we'll all be heating with over unity permanent magnet or HHO boilers .

You said 'Do the Maths' me? Maths? Shurely shum mishtake?

I just checked it was 2005 when I did it. So I might look at it in the next year or so...
Del

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#12

Re: Specific Flue Question

09/20/2008 10:50 AM

I liked the soft start idea...it worked with my wood stove. That column of cold air was just too hard to get moving unless I burned a page of my notebook first.

I had a similar problem with my gas fireplace when I changed from a pilot light to "instant on" electronic start. I went back to the pilot light method...and things were fine...though the gas consumption went up a bit.

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#13
In reply to #12

Re: Specific Flue Question

09/20/2008 10:56 AM

Hey, yes, using my 'To Do' list to warm up the flue every morning would be a huge labour saving device.

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#14
In reply to #13

Re: Specific Flue Question

09/20/2008 12:06 PM

google "The Plant Engineer's Handbook" / 'flue flow'

by R. Kieth Mobley

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#15
In reply to #14

Re: Specific Flue Question

09/20/2008 12:51 PM

If you see the other thread (linked in my post #7) I think I've solved the prob...
I did find a good link to some UK regs etc....I'll try your google too as it's good to learn new stuff.

Cheers

Del

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#16

Re: Specific Flue Question

09/21/2008 3:35 AM

Your problem may be caused from another area, for example if you have had new windows fitted (or you have done them yourself) you may have "sealed" the house up so well that you are not getting enough air coming in to allow the exhaust gases out, till the temperature gradient is much much higher!!

Insulating the pipe may fix the problem, but will lower the efficiency of the boiler as really you want that heat in the house, not outside.....you should only need a few degrees of difference for a chimney to draw well....also, how far up into the chimney does that pipe go, the higher the better of course, to the chimney pot is of course the best, but may need to be of a more flexible nature to allow easy fitting......

Going from a small pipe to a large open chimney, causes the gases to expand at that point and cool down, slowing up the exhausting of the boiler, till it all warms up!!!

This "sealed up" room effect is quite dangerous as it could cause CO to be produced inside the house, though some modern gas boilers (mine for example) has a CO sensor that shuts the boiler down in the event that CO is produce outside of the burner area.....

Try cracking a window (wide open in another adjacent room and leave the inside door open)and see if that fixes the problem. If yes, then see if you can add a small plastic pipe from outside to as near to the burner area as possible with say a 3 cm cross section. Ball up some rabbit cage wire and force in the pipe to prevent mice entering (leaving?) the house via the tube.....that way your boiler will get enough fresh air without removing your warm air quite so much.....

This is the most likely cause of your problems......

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#17
In reply to #16

Re: Specific Flue Question

09/21/2008 3:45 AM

Ta for the input, but the problem has now been solved...There was a slight leak in the pilot light feed pipe connection giving a sooty flame below the pilot light proper which had caused a soot build up over time, and gave rise to the sooty smell and reduced updraught...
When I checked on dates, I found I hadn't serviced it for 3 years (baaaad Kitty)
Del

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#18
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Re: Specific Flue Question

09/23/2008 10:49 AM

Hmmm...You already HAD a pilot light. You didn't tell me that!

The other problem I had with the "instant on" feature of my natural gas heater was that without the little flame to keep them away, tiny mud daubber wasps came in and filled all the little jets. It cost several hundred dollars to get a professional in to de-snag and fix the problem. Since then, I have decided to simply pay the fuel cost to run a pilot light. This is a fairly significant expense, but it will take twenty years of pilot light operation to cover the cost of one service call due to wasps! So, its not quite enough to justify coming up with a mechanical, chemical, or "other" way to keep wasps out of my heaters. To compound the problem, the heaters all use "outside air" because they are being run in a shop which occasionally has spray paint and thinners being used and are pretty tightly sealed. It is a major operation to get into the heaters to service the jets.

And come to think of it, I have not serviced my pilot lighted heaters now for more than three years. So in preparation for a new winter season, I have examined them, and by gosh, didn't I find a couple of field mouse nests! in the flue! OMG!

So you think the question about the wasps would be a good question to ask the forum? Or is it too specific?

Regards.

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#19
In reply to #18

Re: Specific Flue Question

09/23/2008 10:58 AM

So you think the question about the wasps would be a good question to ask the forum? Or is it too specific?

No matter how specific a Q, some one will always manage to answer something else instead!
Del

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#20
In reply to #17

Re: Specific Flue Question

09/24/2008 12:19 AM

Del, appropo of nothing probably, but I have noted a phenomena that occurs with my gas fired hot water heater that may or may not be applicable for your situation. When my water heater fires up, for a few seconds until the draft is established, natural gas can be smelled (smelt? is that a word or is that a fish?) emanating from a bit that acts as an air amplifier using the coanda effect that sits on top of the water heater (don't ask me what it is called, I have no freaking idea.) it stands off from the top of the heater by about an inch or so and the flue connects to the top of it. After the burner has been lit for half a minute or so, the odor goes away. I have been assured by the gas company that this is normal.

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