Using an existing B-type gas pipe to ven
Nailgun007
| Posted in Energy, Heating & Insulation on
I wish to tie into an existing B-type natural gas pipe to vent a natural gas type fireplace. Is this possible to do safely? I have seen the T type of connector and is this OK to use? I am about 20′ away from the source of this B-type pipe , a natural gas boiler.
Thank you for your thoughts on this.
Replies
Does this vent already serve an existing appliance? If so, you cannot simply tee into it with another appliance--you will need to increase the size of the entire vent downstream of the tee. If my memory is correct, I once tied a 3" water heater vent and a 4" boiler vent together and that required a 6" stack. Check with your building inspector about it.
Absolutely not.
Even if it was big enough to handle the additional btu's from the fireplace, you are way too far away.
I was assuming he meant that the boiler was 20' from the fireplace, but that the vent ran conveniently close.
If the fireplace is 20' horizontally from the nearest section of pipe then you're right... no way.
like he said, absolutely not, if you check your manuals they will probably both state they can not share a vent with another appliance ..
Thanks for your input. I was out of town and just now got to your response. The boiler is about 20' below the gas fireplace and I thought that I could tap into the B-type pipe that is out of the boiler with a T section of pipe.
Thanks for your help with this problem. The reason I am considering this type of connection is that the hot water heater, located next to the boiler has a pipe that is taped into the B-type pipe exhaust.
Yours,
Nailgun007
"20' below" is different than "20' away".
If the 20' is a horizontal distance, then no way.
If it is a vertical distance, then there is a cautious "maybe". You still must ensure that the piping is sized to accomodate the total BTU's at the boiler + fireplace junction.
Bear in mind that there are different tables for natural draft and fan assisted appliances.
If your boiler is a positive pressure discharge, then again, no way. Positive pressure venting is not the same as Type B vent.
>>Bear in mind that there are different tables for natural draft and fan assisted appliances.>>If your boiler is a positive pressure discharge, then again, no way. Positive pressure venting is not the same as Type B vent.Also keep in mind that fan assited is not necessarily the same as positive pressure venting.I don't see many boilers in my area, but the "80+" fan assisted furnaces I see i my area are not positive pressure. Based on my experience measuring draft as part of my Carbon Monoxide Analyses services, they generally "pressurize" the vent for no more than 1' to 18", although that varies.
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Sojourners: Christians for Justice and Peace
Edited 8/19/2005 10:16 am ET by rjw
A lot of information and incomplete and misleading information in this thread.
Based on what I've learned over the years:
As mentioned, the size of the vents (FWIW, I prefer to use the term "flue" to avoid confusion with other components in houses) depends on a number of factors, including (i) the btu's being handled, (ii) the efficiency of the combustion appliances, (iii) and the configuration of the system (e.g., run and rise.)
The reason you can't tie the two components you mentioned together hasn't been listed here: you cannot use the same flue for appliances on different levels of the home.
To clear up some other inaccuracies in the thread: you can (at least in theory) have a 20' horizontal run of flue, but then you'd need at least 40' of rise - fairly uncommon in residential construction. (/No more than 1/3 of the length can be 'horizontal' - and remember none can be truly horizontal, you need at least 1/4"/foot rise on a "horizontal run.)
The use of "T"s to join 2 appliances is allowed in some areas, but is, in my opinion, a poor practice: a "Y" is much better.
In my testing I have found that when a water heater is "T"ed to a furnace* flue, when the furnace is running and the water heater kicks on, the movement of the flue gases from the furnace will sometimes form an air curtain and block the water heater flue gases which consequently spill (aka "back draft") from under the water heater draft bonnet (aka "drafthood" or "draft diverter"**)
And in some rare cases where the draft inducer/fan assist is overpowered (wrong size installed?) when a water heater is "T"ed to an 80+ furnace, when the 80+ runs it can force flue gases back down the water heater flue and also cause backdrafting.
I've never see either event when a water heater is "Y"ed into an 80+ flue. It is still possible, of course. (See the bolded section, below.)
Also, "fan-assisted" is not the same as "positive pressure" venting. On 80+ furnaces, the purpose of the fan-assist (aka "draft inducer") is control the movement of air and flue gases through the combustion chamber including to keep the furnace from burning if the unit is backdrafting air down through the heat exchanger - say, if there is significant negative pressure in the combustion zone when it lights off.***
Finally, and most importantly, perhaps: you can follow all of the "rules" and tables you want, but the final operation of the flue and components is the responsibility of (i) the designer of the system and (in my opinion, at least) the installer of the system.
The ASHRAE venting tables specifically provide that they are "guidelines" only and their application may not be appropriate in any given situation depending on local conditions.
The ASHRAE tables put responsibility for proper operation on the "designer."
I include the installer because (i) usually the installer is the "designer" and (ii) often the installation varies in some details from the design and (iii) s/he is the person on the spot who could actually test operation with a draft gauge.
-------------------
* natural draft or 80+ draft-induced furnace - but not a positive pressure (and I've never seen a positive pressure 80+ furnace in a residence - as opposed tom 90+ condensing furnaces which use plastic flues)
** For purists who object to the term "hot water heater," the term "draft diverter should be "backdraft diverter." <!---->
***This would be extremely rare in a natural draft furnace because the draft hood and the burner position in the heat exchangers are so close together they will (always?) be in the same pressure zone - on an 80+ there is no draft hood and it would actually be rare for the opening to the heat exchanger to be in the same pressure zone as the top of the flue.<!---->
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Sojourners: Christians for Justice and Peace
Bob, you may know the answer to this question. Why the draft hood on water heaters? They don't exist on other natural draft appliances. Why not a direct shot into the flue, as on a woodstove?
AndyAndy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
so air pressure changes don't suck or blow out the piolet light.. the flue to combustion chamber on a WH is in line unlike most other gas appliances...Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!---->
WOW!!! What a Ride!<!---->
Forget the primal scream, just ROAR!!!
Makes sense. Thanks.Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
As IMERC said: but there are drafthoods on "natural draft" furnaces, they just aren't as obvious.On a natural draft furnace, get low and look up: the "box" that the flue rises out of doesn't have a bottom! More later...
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Sojourners: Christians for Justice and Peace
We can use multi-story venting, but the design is more complicated than single story.
Can you go into details?
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Sojourners: Christians for Justice and Peace
Keep in mind that it's Canadian code and not chapter and verse. It is primarily intended for apt. that have their own water heaters or furnaces. But it does allow for single family buildings. You could have a furnace for each floor sharing a common chimney. The appliances must have a draft hood or be certified for use with type B venting.
Thank you for your very good answer. I guess I will just have to run a separate pipe for the gas fireplace.
Yours in Wood.
Nailgun007
riw has you covered, I'll only add install a carbon monoxide detector near your gas appliance, it could save your life. Lots of lick.