Why don't more oil burners use outside air?

BinDerSmokDat

I was just wondering why more oil burners do not use outside air?
I know in wood stoves and some fireplace designs, an outside air tube is used near the combustion to minimize drawing cold air through the home.
I know there are kits available, but from my limited experience with oil heat, I haven't seen many.
Why don't more oil boilers use this?

STEVEusaPA

They should. Tighter homes, commercial style (larger) range hoods and high efficiency dryers suck all the combustion air out of the house.
Uniformed people (and techs) are unaware and declare oil is dirty and unreliable (nuisance calls, soot, etc) and switch to gas.
Then when they put in a new gas furnace, whatdoyaknow...outside air.

SuperTech

Plenty of the oil burners I work on use outside air, wether it's directly to the burner box like 9/10 Energy Kinetics boilers I see, a regular cast iron boiler equipped with an air boot or just a simple "fan in a can" in the boiler room, there's plenty out there.

And the burners stay cleaner too when they aren't sucking in dusty, dirty basement air 😉

EdTheHeaterMan

#1 Economics. The customer will purchase the lower price. So adding an intake pipe, (on a non-condensing appliance where it is not required by the installation manual) won't increase sales!
#2 Tradition. Traditionally oil heat was installed in older homes that had enough combustion air. As tighter home construction developed over the years, Gas furnaces also became more efficient (condensing furnaces) and found easy venting without a chimney. Adding a second plastic pipe was easy and made for better combustion in tight homes.
#3 Technology. While oil furnace can also be made over 90% (Condensing) the manufacturers that have tried this technology have had limited success with marketing the product. So the easy plastic vent thru the side wall is a very small percent of oil heat appliances in service.

Follow up: If you have enough combustion air in the basement why bother with the added installation cost?

Not saying it is the best practice ,or that it is right or wrong. just answering @BinDerSmokDat query

kcopp

The only thing I will add is that in some cases drawing in Very cold combustion air into a burner can create some serious problems w/ how well the oil is atomized into the combustion chamber. I have seen this especially w/ direct or balanced flue oil boilers.
It changes the whole burning process and will lead to problems.

BDR529

Not everything is created equal. Always a trade off..

BinDerSmokDat

Thanks for the feedback guys.
My thought is I would rather have the boiler drawing cold outdoor air through a duct down in my unoccupied basement directly to the boiler, rather than creating drafts through gaps and openings on the living level.

Cost doesn't seem too bad, the Beckett air boot kit is $113 from the local supply.
I can see it being a slight PITA when servicing, one more thing to disconnect. Maybe that is the real reason more aren't installed.

So for a basement install would you insulate the duct? Or do you not bother insulating the duct as it might warm up the incoming air a little?

STEVEusaPA

You don't insulate the duct. You want it longer than shorter so the combustion air warms up a little-I think they recommend at least 10 ft.
And of course, you definitely have to set up the burner afterwards-draft, smoke, analyzer or you'll soot the boiler/furnace right up.

BinDerSmokDat

Heating up the outside air a little was what I thought would be the better option.
However I don't think the Beckett Air Boot set-up is an option for me right now.
Instructions say do not exceed 44 feet of duct, counting each elbow as 7 feet of duct.
Currently the boiler is on the back side of a central fireplace, with the burner intake pointed towards the underside of a staircase with doubled joist and extra supports I'd need to get around. The only place I could rout the vent is on the other side of the house.
I'm counting at least 5 or 6 elbows and about 24 feet of straight duct to the vent point.
I could do it in 3-4 elbows but then the duct would have to literally run through the middle of the boiler room area and then the living area.
Ah well, I'll keep it in mind for if I remodel the back of the house.

STEVEusaPA

Then you should go with a fan-in-the-can option for bringing in make up air.

BinDerSmokDat

That is an option I wasn't even aware of, I just looked it up.
So basically the same concept, but it has it's own blower blowing air into burner area, versus the burner drawing air through the duct. I will look into that.

STEVEusaPA

BinDerSmokDat said:

That is an option I wasn't even aware of, I just looked it up.
So basically the same concept, but it has it's own blower blowing air into burner area, versus the burner drawing air through the duct. I will look into that.

@SuperTech mentioned it in his first post.
Yes, wired properly into the burner circuit as a safety.

Larry Weingarten

Hi, Couldn't you just go one size bigger with the duct? That would slow flow and cut friction losses.

Yours, Larry

STEVEusaPA

One size bigger on what duct? Not the flue pipe.

captainco

Is piping cold outside air directly to a burner a good idea? What happens to things when they get cold? They contract and bunch together. Their molecules move slower. Their surface area is reduced. You might compare this to putting sugar in cold tea versus hot tea. Doesn't seem to mix in the cold tea very well. If a burner is set up when the outside air temperature is 40 s degrees what will happen when the outside air is 10 degrees? The combustion process will totally change. Like it or not, combustion air needs to be heated to mix properly. Also during the off-cycle, cold outside air is still being pulled through the burner. This will make the oil in the drawer assembly cold.. Cold oil creates poor light-offs. If you ever wondered why a burner that was set up perfectly at the beginning of winter is all of a sudden sooted up, this might be the reason.

Mechanical combustion air (Fan in a Can) is the best way for combustion air versus piping it directly to the burner. So little is understood about the best way to supply combustion air or how much is really needed. If air is piped directly to a burner it is going to have to be set up on the lean side to be safe!

STEVEusaPA

Don't all modern high efficiency gas furnaces/boilers have their combustion air piped in from the outside?

captainco

Not sure if that gives them more points on their efficiency but it actually lowers efficiency by 2% or 3%.
Lots of equipment have things that really don't make sense. NCI does not recommend 100% outside air directly to any burner,

Robert O'Brien

https://carlincombustion.com/12239-2/

Outside air solves the confined space issue as well as reducing infiltration thereby decreasing fuel consumption. Cold air is denser, set up with a chart

captainco

The air chart verifies that as the air gets colder, the set=up must be leaner. Do we have to go back and change the settings as the weather changes?
Is house infiltration reduced or just relocated? There are no field studies showing lower fuel consumption.

Robert O'Brien

With a 30% excess air level, it's pretty close to 2000 cubic feet of air required per gallon of fuel. Assuming 800 gallon annual consumption,that's 1.5 million cubic feet annually. Want to take it from inside the envelope or outside?