Adding an exhaust fan to a boiler room

[persaverence]

Have a small boiler rm 20 x 10 x 16, room is getting too hot. Located in phoenix az, there is a 5 ton unit that supplies this room and other areas. It has 3 ea 8" drops in the room. Do I want to exhaust more air than the unit is supplying?

[Gib's Son]

No. Unless combustion air is ducted directly to the burner you will have combustion issues because the space will be negative. Consider an HRV or run a round coil and use that heat during the winter.

[vangoghsear]

I agree you do not want to put th4e room under negative pressure. A little more description might help us with your problem.

Does the boiler run year round? (For domestic water, process heat, etc?)

Is the combustion air direct connected to the boiler?
or,
Are there open louvers bringing in outside combustion air?
or,
Is the air conditioning air being used for combustion air with no return or exhaust?

Is the A/C unit keeping up in the "other areas?"

Do you bring outside air into that unit,
or,
is it starved for return,
or,
are you returning air from the hot boiler room?

[persaverence]

I agree you do not want to put th4e room under negative pressure. A little more description might help us with your problem.

Does the boiler run year round? (For domestic water, process heat, etc?)

Is the combustion air direct connected to the boiler?
or,
Are there open louvers bringing in outside combustion air?
or,
Is the air conditioning air being used for combustion air with no return or exhaust?

Is the A/C unit keeping up in the "other areas?"

Do you bring outside air into that unit,
or,
is it starved for return,
or,
are you returning air from the hot boiler room?

Yes, the boilers run year round and the combustion air is ducted to the outside. There are no louvers in the room. There are 3ea Benchmark 2.0 boilers.

Yes, the AC does keep up with the other areas. The air handler is located in the room with the boilers but uses 100% fresh air for return.

[ascj]

What's to hot?

The Benchmark's run pretty cool.......is all the hw piping, properly insulated?

You are trying to condition the room with an 100% OA AHU. What is controlling it? You controlling just by discharge temps or is there a space sensor? Where is the space sensor located?

So your feeding 8" supplies from an 100% OA AHU in a room that is probably pretty tight. Where does the air go?

Again....why are you trying to cool a mechanical room........is there other stuff in there, that can't take the heat?

[xformer]

If you dont have any louvers or return air openings in the room, the room will become pressurized, thus not allowing any air from your rtu to enter the room. Just installing vents or louvers will prob. help. a 5 ton unit that also serves other areas and is 100% make-up air is not going to help too much in phoenix. 6,000,000 btus...Is your breeching/ piping insulated ?