MAKE UP AIR

RICK JAMES

THe boiler is a williamson 105 btu natural gas unit

RICK JAMES

MAKE UP AIR

I HAVE AN ATMOSPHERIC BOILER STANDING PILOT CAST BOLIER
IN A TIGHT CONSTRUCTION , i AM IN ALASKA AND TRYING TO FIND OUT HOW MUCH MAKE UP AIR I NEED , I KNOW THAT THERE HAS TO BE 2 OPENINGS 1 AT LEAST 12 FROM THE LID 1 AT LEAST 12 FROM THE FLOOR ,ALSO ONE PROBLEM IS SPACE THE BCI IS IS 9.5" HIGH 16" ON CENTERS SO SPACE IS LIMITED SO IAM THINKING THAT IT SHOULD BE RECTANGAULAR BUT UN SURE OF THE SIZE 6X12 8X12 ?????? THE AIR IS FROM THE OUTSIDE PULLING IT VERTICALY INTO THE MECHINAL ROOM FROM ABOVE

nicholas bonham-carter

combustion air opening

can you make the opening the same size [in sq. in.] as the openings in the boiler front and back where the burner is?--nbc

Darrell_4

Enstar, the gas supplier, will allow you to have one opening, directly communicating with outside, that is one square inch per three thousand BTU's of appliance input. The opening may be placed anywhere within the room, but due caution needs to be given to freezing and to natural convection that will suck every scrap of warm out of your boiler room.

So, at 105 input, you will need a hole in an outside wall that is over 35 square inches. Probably a 3x12 or a 4x10 opening.

bob young

fusible link

we use a 12x12 fusible link damper. good for up to 1 million btu

Mike Thomas_2

Barrow

When I lived in Barrow, we use to cut a hole in the floor, next to the wall. Then build a 3 sided plywood box, set it over the hole and run it up to the ceiling. On the side of the box, near the ceiling, we installed a louver with damper. This allowed air to enter from the floor, travel up the plywood box, come out of the louver, mix with the very warm air at the ceiling. By moving the damper you could control the amount of air entering the room. Because it entered from the floor, wind did not affect it as much. Mixing cold air with warm, kept it from freezing everything else in the room. I have even installed a few baffles in the box, just to slow the air down if I thought conditions warranted it.

bob young

before the dead men

sounds serious. were you with the lewis & clarke expedition ? lol

Unknown

Air for Combustion

First Rick a small correction in terminology. Make up air is air required to make up air removed by mechanical exhausting, it is in addition to air for combustion. What you are looking for is Air for Combustion.

If you are using vertical ducts which I assume you are as air is coming from above the rule is 1 square inch per 4,000 BTU's. One duct terminating (12")twelve inches below the ceiling the other (12") inches from the floor. The size would be 26.25 square inches minimum a (6") six inch diameter would be 28.3 square inches so more than adequate for your 105,000 BTU Williamson. So you would need two six inch ducts into the room.

There is a one opening rule also which must terminate 12" from the ceiling only. The equipment must have a 1" clearance from sides and back and 6" from the front. It can be a horizontal or vertical duct and must communicate directly with outdoors. The size is 1 square inch per 3,000 BTU's and in addition not less than the sum of the areas of all the vent connectors in the confined space.

Hope that helps.

DrPepper

Rick, listen to Tim....

he is quoting the International Fuel Gas Code, Section 304, and not enough importance is placed on the sizing of CAI. It isn't just the burner that needs enough air to operate properly it's the potential of someone being overcome by CO. It happened here last year in a school boiler room, hospitalized the guy but he is OK. Tims 26 sq.in. is minimum FREE AREA. A frequent mistake is if you use a louver, it cuts about 50% of the free area available. Look it up on the Ruskin web site. All louvers have a chart that shows actual % free area. Ductwork, elbows etc. all restrict the flow of air. If your afraid of the freezing air, use a small hydronic or electric unit heater to blow across the incoming air and warm it. Insulate the piping.

Unknown

Rick,

my manual Fundametals of Gas Volume II includes all the charts and tables for sizing along with my own chart on calculating free area of louvers and grilles. Just e-mail me and I will make a catalog available to you.

D107

question on terminology

Tim is the air that is pushed up the flue by a modern burner with a fan (and also the power venters or direct-vented) considered purely combustion-related and not mechanical exhausting at all? It's certainly more obvious with bathroom and kitchen ventilator..... Gas driers?

Thanks,

David

Unknown

This is a very complex subject

we have several different things being grouped together in one category and they are really seperate. To answer your question in a simple way is to say they are simply related to combustion only. Dryers, range hoods, bathroom ventilators by the way are not considered as vented but are exhaust systems. When on commercial equipment they may be classified as vents.

The deal is venting is related to ventilation (air for combustion). Air for combustion as listed in the National and International Fuel Gas Code are pretty much only for Natural Draft and Fan Assisted Category I equipment.

So lets take fan assisted category I first, this is a fan whose only job is to overcome the resistance of the heat exchanger and bring in air across atmospheric burners to assist in combustion. This allows by the way less air in cubic feet than straight natural draft atmospheric. The pressure in the flue is negative pressure therefore fan assisted can be vented with natural draft and the flue pipe does not have to be sealed.

Direct vent as defined is not always with a fan but is two pipes in one (concentric) flue products out through the middle pipe and air for combustion drawn in by gravity and temp difference from the outside pipe. The deal here is less space required from windows doors and other openings. It can vary according to BTU's from 9 inches to 12 inches.

Power vented is using the blower to actually power the flue creating a positive pressure in the flue and requiring a sealed flue. The air for combustion is usually drawn in to a sealed combustion chamber through another pipe. When vented they are classified mechanical exhausting and must be 4 feet from any windows doors and openings.

Many Mod/Con systems use a combustion blower in conjunction with a negative pressure gas valve. In this case the blower acts to cause the gas at less than atmospheric pressure to be drawn out of the valve premixed with the air before burning and pressurizing the flue.

Hope that in a few short paragraphs answers the question. There is a whole lot more to all of it believe me and in many cases installers are not very well versed on this subject along with other related combustion subjects.

bill_105

who did this?

It was either Mountain or Bell or Yourself. Regards to John.