Flue Size

Bruce M.

Is there any advantage in a boiler with a 6" flue oulet to use a 6" by 5" adapter and use 5" flue pipe. I am wondering if there is any venturi effect or velocity to be gained this way.

David Efflandt

Are you joking?

Maybe you are taking something you heard out of context or do not fully understand it. Pressure is inversely proportional to velocity, but that is perpendicular to the flow. It would tend to increase velocity head (and headloss) which could decrease flow. Hopefully your spill switch would save you before you become another CO statistic.

If someone suggested a larger heating device than worked in the past, and you have not expanded your home, I would suspect that it is oversize.

Bruce M.

I did not explain the question correctly.

A certain hot water boiler comes with a 6" flue outlet and the manufacturer gives the installer the option of using either a 6" flue pipe or an adapter in order to use a 5" flue pipe. The question is; would the stack loss be lower with a 5" flue pipe or would it be the same? Which size would give the optimal performance and why?

jim lockard

I will try

NO the flue /chimney needs to be sized to the load (BTU's)and the height of the chimney. You will need to have the proper size liner installed in your chimney if not there already. As for the adaptor read the install book. J.Lockard

Bruce M.

Best reference

Thanks Jim. What would you recommend as a good source of information for correct sizing.

Ken_8

Say what?

With the information you have provided none of us can suggest anything.

If the boiler is non-condensing and the AFUE is ~85% or less, and the chimney is within the home (as opposed to an outside wall) there is no need to line anything - unless your existing chimney doesn't even have a fire-clay liner of its own - or if it is damaged somehow.

Depending on how cold your area gets, the nature and configuration of the existing chimney, the efficiency of the boiler and the venting tables that are appropriate, you may be fine with either 5 or 6 inch connector.

The vent connector is the pipe that runs from your boilers's breeching and/or vent hood to the masonary chimney you may already have. As long as the manufacturer suggests either 5 or 6 inch is allowed, go with the which ever suits your situation. Somehow however, a transition piece sounds like it would be required. The draft hood is already either 5 or 6 inch.

If the unit is oil and you are talking about a draft regulator - everything I said above is wrong.

Assuming that is the reality of your question, it would make little difference either way. Either would control draft swings well.

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Bruce M.

Non-condensing oil fired

hot water boiler. Chimney is lined and is on an outside wall. Company states a draft regulator is optional but not required. 6" X 5" adapter would be required to use 5" flue pipe.

Ken_8

I would use 6\" and a

draft regulater!

The reasons?

A 6" connector pipe from boiler to chimney will afford less chance of restriction. A draft regulater will allow optimum air intake at the burner - especially with the large temperature swings an outside chimney will invoke (and the resulting fluctuations in effective draft).

I cannot recommend too strongly that a combustion test kit be used to dial in the burner after you get the pipe and draft regulater installed. Remember to put at least three sheet metal screws in each smoke pipe and tee/joint. Also make sure the connecter ends flush with the chimney interior liner. Use mortar mix to point up the pipe to chimney joint. If the annular ring between the pipe and masonry is more than an inch-and-a-half, center the pipe with pebbles/rocks and point up the voids.

It should be fine.



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Bruce M.

Thanks Ken

Much appreciated.

Bob Harper

no liners???

Whoa Ken, how can you state he doesn't need a liner in a chimney you haven't seen? What if it is over sized? If it's much less than about 300,000BTUs in an 8x8 clay tile lined chimney it's oversized. Now, add to that a rotten or missing mortar joint every 2 feet.
NFPA 211, 54, and 31 all call for an inspection of the chimney before installing new equipment and repairing or relining it to meet the service rating of the new equipment. By installing new equipment into old rotten chimneys, you are exposing your customers to CO and loss of efficiency while exposing you to liability. What is this hang up with HVAC and boiler guys about not demanding a proper set of lungs for their equipment to breathe?

jim lockard

Thanks Bob

Thats what I was trying to say line the chimney. We had one the other day where the products of combustion from the gas water heater were coming out the draft hood on the boiler,looked really cool. The chimney was full of holes and would not draw til we installed a new flexell liner now all is well.

TORCH_2

Might not be the right thread or tell me the right one i'm new here

Hi I have a welding shop in a old shipping container for my self and I am going to be installing a very old heatarola Intency fire air duct coal stove but I'm burning wood in it and would like to use 6in flue instead of 7in since 6 is easier to get at my hardware store does any one know if it is ok in the long run? I have used the stove on 6 before but not vented in to any chimney I did it to warm a outside party I had!! or should I just use 7 if i can find and the parts and pipes? Also when I install it in my shop. I plan on venting the stove out and turn left horizontal into a raised up 35gal drum on it's side with one removable baffle and then out the top of the drum and through the steel container wall in to the next room and turning right in to the I think 14 or 16in 15 foot round concrete chimney ( Made out of old non used sewer pipes) total single wall flue before chimney aprox 10feet and 3 90's and one 45 going into the drum, but I can remove The 45 if I have to and pipe the stove into to back of the drum and out the top front . Will this thing still draft right ?? or will it take a long time to get going?? Thanks to any one or people with tips or help or ideas Thanks BEN AKA TORCH PS. If more info is needed just ask!!!!

icesailor

Wood Stove Flue Sizes:

This is a very old thread.

There is no code that I am aware of that will cover what you are trying to do. It may or may not work. I no of no vent tables that cover home made barrel wood stoves but it may work.

Install quality Carbon Monoxide detectors that work and don't take the batteries out if it goes off.