air flow to a boiler

[cgregor]

Hi, all. A newbie here.

I'm replacing an oilburner with a wood gasification boiler. Haven't yet picked out the brand, but I do want to supply it with outside air in the name of heating economy. Here's what it will take: a 20-foot-long below-grade pipe, diameter at least 12", possibly more, coupled to the air intake. My questions are, what are the friction losses involved in airflow through a pipe and if the boiler specs give a cfm reading, how do I determine if 12" is adequate for 20' to meet the demand?

I just ran across this site today and am soooo glad to have found it!

 

[tom in maine]

12" is way too big if you are concerned about pressure drop. I suspect that there would not be a lot of earth tempering of
incoming air on such a short loop, especially in Vermont in the wintertime.

I am not sure about the economy of the concept in terms of heat savings. This comes from a guy who lives in an R-65 house.

Welcome to Hearth. You landed in the right place.

 

[cgregor]

Thanks for the input, Tom.

I'm big on small carbon footprint, and the State has had a Button-Up program (losing funding, unfortunately) which dealt with energy conservation. The biggest loss is not insulation, but air leaks. I'm re-habbing a house and don't want the boiler to be contributing to any leak problems (or, if the place is really tight, defective combustion and possible CO poisoning!), so I am looking at putting a pipe in before I pour the concrete pad in the basement. I just need to be sure that the diameter of the pipe is adequate for the needs of the boiler and the length. I hadn't thought of any tempering effect, but I'm glad to hear it's not a concern. Groundwater temperature here is 45, so I don't imagine it would be a concern anyway....

chuck

 

[WoodNotOil]

Welcome!! Another Vermonter!

I understand where you are coming from with wanting the air feed, but my concern would be with blowing cold outside air directly into the boiler. I know that Econoburn decided to preheat combustion air on their new outdoor gasifiers and I assume they had a good reason for going to the trouble. I would think the effect of the the fan running on draft in the house would be fairly negligible. Even the most uptight guys on here about efficiency and super insulating haven't put in external air feeds to my knowledge...

 

[Frozen Canuck]

You might want to check with your local building code officals about suppyling outside air to a combustion appliance. Here all combusting appliances must have outside air piped directly to the unit for combustion. If you have a tight home you are forcing it into a negative pressure situation. We only do this (negative pressure) when we are doing a mold abatement treatment on a home as the negative pressure stops any mold spores from leaving the room we are working in & spreading to the rest of the home. If you have a drafty home you are forcing outside air to come in anywhere it can to replace the combustion air, think more/larger drafts; then you warm that cold air up, wasting energy in the process. All of the above are things you want to avoid.

 

[cgregor]

thanks for the tip. I'll be meeting with the first of them next week, and I'll ask about that.

chuck in Vermont (the banana belt to you guys!)

 

[Frozen Canuck]

Ha, yes banana belt for sure. I bet you don't see alot of -40 there.