Combustion air for boiler

LD

We have a Viessmann Vitogas 050 (either 100 or 115 MBH) boiler with an indirect tank in our house's mechanical room (approx 6' x 7'). The room has a door. It gets quite warm in there.

I don't recall seeing any grills for combustion air. There is a stainless pipe for venting the boiler.

Is this normal? I'm assuming all is okay since I am not the first owner of the house but I just wanted to make sure I'm not suffocating the boiler if I close the mechanical room door.

Thanks for any comments.

Mr. Smith

national fuel gas code

requires 50 qubic feet per 1000 btu/h for combustion air in confined spaces.

115000 x 50 = 5750000 / 1000 = 5750 qubic feet of space required.

your room 6 x 7 x 8 = 336

you need venting, one high vent and one low vent that equals 100 square inches. (or more).

we usually use 2 - 6 x 10 return air grills, giving plenty of venting.

hr

The Fuel Gas Code NFPA 54

now has an alternate method (chapter 5 A.5.3.3 (b)2 allowing just 1 opening up high. For natural gas I like this method beter as it seem to cut down on convective currents that steal warmth from the boiler and piping in the room.

This alternate was introduced to reduce the risk of freezing water pipes and limit low temperatures in mechanical rooms. According to the explanation in the NFPA 54 Handbook.

For LP, as it's heavier than air, I still prefer the high and low method. Better to lose some heat to the outdoors than risk a room with LP lying on the floor from a small leak.

NFPA 54 codebook explains this and the Handbook version shows examples. An excellent book that needs to be read, and on every contractors shelves

hot rod

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Unknown

New NFPA 54 2002 takes it a step further

there are now 5 methods for determining air for combustion:
1. 100 percent indoor air

2. 100 percent outdoor air

a. Two permanent openings ((been in there for years)

b. One permanent opening (introduced in 1996 code) this is the one Hot Rod refers to.

3. A combination of indoor and outdoor air

4. An engineered system

5. A mechanical air supply

In addition they have eliminated the definitions of unusually tight construction, confined space and unconfined space. The terms were eliminated because they no longer denote one single value (50 cubic feet per 1,000 btu), but varying volumes, depending on the method used and the amount of air infiltration.

The standard method still uses the formula to determine if air is needed. The Known Air Infiltration Rate Method (KAIR) is now also used. It is based on a determination of Air Changes per Hour (ACH).

I am presently working on writing a set of easy to follow easy to understand instructions for determining Air for Combustion using the new code. It has been a little intense as they have made it somewhat complicated but I am sure I will figure it out. That in addition to numerous mathematical errors in their calculations

Mr. Smith

the

west coast has not yet adopted the NFPA, but I do use it from time to time.

HR, is this in the new book? mine is a couple years old, time to update the books I guess!

Mr. Smith

Unknown

The new NFPA 54 2002

has been out for a while. The Handbook has been in print since July this year. It is available from

National Fuel Gas Code

National Fire Protection Assoc.

One Batterymarch Park

Quincy, MA 02269

or at www.nfpa.org

The handbook is in addition to the Code book itslef. It explains very clearly how to apply and use the code.

DL

There is a vent but...

I must be blind. I took a closer look at the mechanical room and noticed a galvanized vent pipe leading from high up on the wall down to about 6" from the floor. It isn't connected to anything so it's obviously just an air intake.

Now, with the calculations you've been so generous to show, I wonder if it's enough air.

The pipe is approx 6" in diameter and I estimate about 8 feet in length (mainly running from wall down to just off the floor).

Is that enough air?
Thanks so much guys!

Steve Ebels

6\" pipe

Six inch pipe yields approx. 28 sq inches of area. This may be enough, may not. The determining question would be, where does that pipe terminate at? Does it just go into a room adjacent to the mechanical room or does it go all the way outdoors?

LD

Pipe termination

The pipe goes outdoors

Steve Ebels

Code allows

With direct outside air to the mech room code allows 1 sq inch per 4,000 btu's of input. 4x28=112,000 btu's You should be OK. It is however, ALWAYS prudent to check by turning on all fuel burning equipment, exhaust fans and dryer and observing whether your flue starts to backdraft.

Read through the other post titled "air for combustion"