Flue distance to slate cap

[BachIsGod]

Hi everyone,

Long time lurker here. I've been wanting to post my story for some time, but I have been working on my home heating system on/off for the last year.

I have one question that I need help with. I had a chimney sweep inspect/clean my boiler/furnace flue. He said there is no damage and it is clean, BUT he said I should raise my slate cap to get a better draft. It is about 5 inches now, and he recommended at least 8 inches between the end of the flue and the cap.

Is that a recommendation I should take? I run my boiler and furnace through this single ~8*8 flue. Here is a related picture of the cap and distance.

 

[maple1]

My first instinct is that it is fine that way. Most stainless caps only have a couple inches. But that is a big cap - not sure that matters or not but maybe a chimney expert will chime in.

Does it draft/work ok?

 

[BachIsGod]

My first instinct is that it is fine that way. Most stainless caps only have a couple inches. But that is a big cap - not sure that matters or not but maybe a chimney expert will chime in.

Does it draft/work ok?

The HVAC person said he thought the boiler wasn't getting a good draft. He made this observation by looking at the burner through the pilot hole. The chimney people didn't observe the boiler in operation. They just made the finding about the distance. It is tough to guess who is right, but given that this has been in place for 70 years, I'm leaning towards keeping it as is

 

[grader]

read the draft with a manometer at the boiler or furnace. the gap should be enough but the reading is what matters.

 

[maple1]

I would be suspect of that HVAC person. Any decent boiler tech will actually measure things.