Fan In a Can and Managing Cold Air (Part 2)

NewGuy

Someone posted this question but it was fifteen years ago. I figure folks have more experience with FIC by now, so it's worth asking again.

I'm about to have a Fan in a Can installed to solve some air problems. My new boiler spill switch kept tripping. Then the boiler kept turning off/firing up over and over. The math says I need lots more make up air. And the success I've had with the boiler when leaving two basement windows open agrees.

BUT. With two windows open I'm losing a ton of heat that generally rises into the building. Or what I should say is that a ton of cold air is coming in.

Will this be any different with the Fan in a Can? It sends in cold air plus allows more to pass in when its not running. Will it be the same heat loss? Maybe I should just put metal grates on the windows and leave them open?

Is there a new philosophy or technology for this dilemma?

Here is a link to the post from 15 years ago. The result was a short debate about adding a damper vs not adding a damper, and maybe realizing that FIC is strictly for enclosed boiler rooms. https://forum.heatinghelp.com/discussion/122914/fan-in-a-can-and-cold-air?utm_source=community-search&utm_medium=organic-search&utm_term=fan+in+the+can+cold+air

neilc

the can fan should only run while the boiler runs,

would you be fanning an entire basement, or a dedicated smaller room ?

psb75

You could install a passive cold-air down-pipe with a j-trap in it. 3"-4"-6" dia. pvc. or even dryer-vent pipe. The boiler could "pull" whatever it needed when operating. I have one in my basement root cellar.

Jamie Hall

Ideally the boiler should be its own room — doesn't have to be fancy or all that tight, but still — if you are going to use a fan in a can (or any other approach to outside combustion air except for direct ducting). Then run it when the boiler is running (it must be interlocked). Do you need a damper in such a situation? I'd be inclined to say not really — probably more hassle than it's worth.

EdTheHeaterMan

First of all, the means that you provide combustion air by opening windows does not meet code requirements.  The combustion air MUST be a permanent opening that doesnot have a means to close off the openings.  “And the success I've had with the boiler when leaving two basement windows open agrees.” indicates that there is a way to close off that source of combustion air.   

The logic is this.  As the homeowner YOU know that those windows need to be open.  As a Homeowner on Vacation or in the Hospital the person doing you a favor by looking in on your home does not know that window needs to be open.  So as a favor to you they close that window because it is so cold out.   The burner then fails or soots-up or both.  The cold weather causes the pipes to freeze and you come home to an insurance seminar.  

You need to have a permanent opening that cannot be closed in any way.  The Fan in a Can is one way to accomplish that.  But the burner must be connected to a prover switch to be sure the combustion air is available.  

You can always just do what is in the code book to solve your problem. Permanent ducted ventilation to the boiler/furnace location.  Make the ducts exactly the right size to reduce the amount of outside air to the amount needed.  Opening a window may be overkill.  Do the math!

JUGHNE

This is part 2 of combustion air problem for this OP…..I believe.

You could put one Fan/can in for the boiler.

Another for the 6 WH's you have.

And let the dryers run with the basement air that is available.

If any of the other appliances call then it will bring in enough air for dryers plus the other burners.

The Fan/can has to be interlocked with the burner controls and will start first, prove that there is pressurized air available and then start the NG burners as called.

As far as off cycle cold air, if possible run the duct up high from the inlet and then down to the can. This may limit the mitigation of cold air thru the can.

NewGuy

https://forum.heatinghelp.com/discussion/comment/1828743#Comment_1828743

Yes, the can will be attached to the burner.

The duct will run to the boiler but can fan the entire basement. The boiler is inside about 3.5 walls. The fourth wall is only half as long as the rest with an opening towards the back exit. It's also only about 80% as tall as the others, due to pipes etc. passing overhead. Three of the walls are just wood planks, sideways like siding. The fourth is the stone house foundation.