Question for the heating pros

[MIJarhead]

Hey all...

I am planning to install a 50k natural gas heater on the ceiling of my detatched garage woodshop.

The unit calls for 3” flue piping.

The previous owner had a wood burning stove in the space which used an 8” flue which I removed...however the stack from the ceiling up to the chimney cap remains in place.

My question is can I run the 3” flue into the bottom of the 8” stack and be done with it or do I need to run 3” all the way to the top of the flue stack?

Thanks in advance.

 

[LS6 Tommy]

Sorry to say it, but it's the stack has to be 7" or less.

Tommy

 

[BD1]

I would call manufacturers tech support.
A single chimney is normally ran large enough for two appliances. I would say 3" into 8" is fine.


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[TractorJeff]

I would call manufacturers tech support.
A single chimney is normally ran large enough for two appliances. I would say 3" into 8" is fine.


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Probably most times ; "Yes!"
But on the new fangled woodstoves (EPA Certified) a smaller outlet into a larger Flue will actually over draft the Fire.
I am not sure on a Heater like he is installing but would think that the pipe would condensate a lot because of not heating the pipe surface area enough do to heat cycling.

 

[yeldogt]

What is the flue made out of ....?

My guess is if even metal .... the manufacturer will have the need for a 3" all the way. it is about condensation .... you will not have enough heat (energy) to properly exhaust the combustion gasses once it opens into the larger pipe.

Years ago it was common to see tank water heaters going into larger flues -- they had much larger burners back then and stand-by losses greater than today. the flue would stay warmer. Even then --they would condense and cause problems. That's why you see the metal liners ...

 

[BD1]

Probably most times ; "Yes!"
But on the new fangled woodstoves (EPA Certified) a smaller outlet into a larger Flue will actually over draft the Fire.
I am not sure on a Heater like he is installing but would think that the pipe would condensate a lot because of not heating the pipe surface area enough do to heat cycling.

Isn't that why they have dampers and vents ? Again, contact manufacture.


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[Jackfre]

To get the best operation and reliability out of the unit, you should line it with 3” all the way.

 

[LS6 Tommy]

I would call manufacturers tech support.
A single chimney is normally ran large enough for two appliances. I would say 3" into 8" is fine.


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7" is the max on 3" unit outlet. It's called the "7 times rule".

Tommy