Fan In A Can

JakeCK

Maybe a bit of a hypothetical question here. Can/do the fan in a can system from fields control increase the efficiency of the building by supplying combustion air and avoiding the air getting pulled in from other uncontrolled areas?

Jamie Hall

A resounding maybe. Sometimes. Way too many variables…

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1803678#Comment_1803678

I'd expect them to intentionally run positive pressure, so excessive infiltration when running.

JakeCK

https://forum.heatinghelp.com/discussion/comment/1803683#Comment_1803683

But its easier to seal up a boiler room than a whole building.

JakeCK

In my house, when my boiler fires it can pull my basement door shut if its with in a few inches of being closed already. Thats a lot of air getting sucked in from all my windows and doors.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1803685#Comment_1803685

This is true. So if you are using a fan in a can to pressurize a sealed boiler room or sealed combustion chamber system, which is called forced draught, you won't have the air coming from the rest of the building. But whether that increases the overall heating system efficiency (not just the combustion efficiency) is a far more complex question.

If we were talking about a power plant here — say the power plant on an oil fired ship — forced draught can, and on warships often was, significantly increase the power available from the system. It did not increase the efficiency of the system, however. The same thing is true of a heating system, though it is harder to measure system power never mind system efficiency.

JakeCK

And forced induction also increases the power of a muscle car as you hear the whine of the whipple. Or with an ecoboost it means Ford can shove in a vehicle a smaller engine then would normally provide adequate performance and, atleast theoretically, allow greater efficiency by keeping the heat engine closer to 100% output and closer to the carnot limit.

But I wasn't concerning myself with the power or efficiency of the heating plant its self. Just with the idea of keeping the boiler from affecting the rest of the house.

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1803688#Comment_1803688

I suppose this is one of those things that greatly depends on the house and it's layout.

In my house it would be very hard to seal up the basement. Also, my infiltration is much higher into the basement so mine is the opposite of yours.

What about just an open vent to the outside near the boiler rather than a fan? If you can put the "draft" near the boiler it'll stop pulling from the house.

JakeCK

I've thought about that but it would be difficult to get a sufficiently large hole on the side of the house in that corner. But it would be ideal because its simple and less things to break. Another issue is the neighbor and his snowblower…

As I continue to work in the basement its only going to get tighter too. I already have most of the foundation up to r13, and in the not to distant future I'm going to sprayfoam the rim joists and overlap that on to the polyiso and up to the bottom of the subfloor. And foam all of the penetrations for wires and plumbing. Even the side door which is at the landing going to the basement is sealed unusually well, and its the original cedar door too! The original frame was warped badly so I just replaced the frame with modern weather stripping. Opening the door feels like your opening a vacuum chamber when the storm is closed. In the winter even while the boiler is firing you can't feel even a whisp of cold air by that door.

Jamie Hall

If you are getting the basement tight enough so that opening a door to the basement has a feel of some pressure resistance when the boiler is running, you need more air getting in there — and an unpowered vent is the simplest and most reliable solution, but a powered intake can work as well — provided it is interlocked with the boiler so the boiler won't run unless it is running.

And a further word: be aware that the intake draught conditions will affect the combustion adjustments on the burner. Once you get your venting arranged as you want it, have someone (if you don't have the needed instruments) readjust the burner for best combustion.

JakeCK

https://forum.heatinghelp.com/discussion/comment/1803700#Comment_1803700

It isn't much pressure, and the door has to be with in a few inches of being closed but it will pull it shut once it is that close. The solution thus far has been to just leave the basement door wide open, which worked fine especially since the cats need access to the basement for their needs.

ChrisJ

@JakeCK

Is that an atmospheric boiler or a power burner / oil burner?

If you already said I apologize.

JohnNY

If I were you, I'd run the duct and not install the fan. A passive intake is usually fine in most cases, even if it's just a 4" round pipe. It's a lot of air without the additional hardware.

JakeCK

https://forum.heatinghelp.com/discussion/comment/1803704#Comment_1803704

Atmospheric. Old weil mcclain.

JakeCK

I was rereading the manual for my boiler and is this correct? 3" seems awfully close to the front panel. O.o

And how well do louvered bifold doors work for allowing air? I've seen these packed in closets before and eeek is all I got to say.

EdTheHeaterMan

3" is from a combustible door.    DOOR being the operative word here.  And the louver on the door has a minimum free space measurement.  That will depend on the BTU input of the burners.  That particular diagram shows a solid door with a louver grill 6” from the top of the room and 6” from the bottom of the room.   When using a full louver door, that will have more free air space than the two grills will provide. and that is more than the needed minimum.

And looking at the location of the actual flame being at least 7” behind the boiler's front door, that would be a total of 10” from the louver door.   If there is no door, then there is a different minimum clearance of 18” for servicing from the front of the boiler. 

And all these clearances and measurements are minimums that may always be exceeded. Just remember, can not provide less than the minimum.

Steamhead

https://forum.heatinghelp.com/discussion/comment/1803705#Comment_1803705

It is possible to wire up a standard Field stack damper and mount it into a duct like this, to shut off the air supply when the burner is off. The damper's built-in safety switches would keep the burner from coming on if the damper was not fully open. If I was going to do this in my house, I'd go this way.

JakeCK

https://forum.heatinghelp.com/discussion/comment/1803835#Comment_1803835

I actually have a 6" one laying around unused. I would have to size up from 4" to 6" tho.

Steamhead

You'd need two 6x4 smoke pipe reducers. But if the boiler has a 6" smoke pipe and no damper, I'd put that 6-incher right above the draft hood.

JakeCK

It has a 7"