Addressing combustion air requirements for 625MBH boiler room

Frank_the_Tank

Hello Heating Help community,

Long time lurker, first time poster. I bought a Roaring Twenties home in Cleveland earlier this year, and am going through my first heating season at the moment. It has a 2 pipe steam system designed and installed by Mouat, and has since had the coal boiler decommissioned and currently has a Weil-Mclain EGH-125 atmospheric gas boiler installed circa 1982. I've been sealing up holes and drafts all over the place, of which there were many in the attic and basement, and have noticed a pretty strong draft being pulled from the cracks around the door (not weatherstripped) between the basement and the attached garage when the boiler is firing. I presume by sealing up the critter holes in the basement and attic that I've greatly reduced the ways combustion air and make up air can make its way in the house.

Some more info:

- The boiler room has two full size doorframes (doors have been removed) that are open to the rest of the basement, which is 3000 sq ft with 7' plaster ceiling, so 21000 cubic feet. There are no dedicated combustion or make-up air vents anywhere in the house.
- The boiler's input rating is 550MBH and the water heater is 75MBH. There are also bathroom fans, an exhausting cooktop hood with a gas cooktop, and a gas dryer on the second floor (nowhere near the boiler room).
- There is a nice 2' x 2' window (576 sq inches) on an exterior wall of the boiler room that could be used for an inlet air device.

Some questions:
1) I've seen lots of recommendations for Field Controls' Fan in a Can, but it looks like their unit is undersized for my needs. Has anyone used their larger Fan in a Drum with success? Can I use two Fan in a Cans instead?
2) What's the consensus on passive air devices, like a motorized louver in place of the window that would open when the thermostat calls for heat? I've read some horror stories that if the wind is blowing the wrong direction you could get negative pressure on the vent-side of the house and end up back flowing the chimneys and end up with a house full of flue gas.

Thanks for taking the time to read, and I'm looking forward to learning more from this community!

Rich_49

Bringing air in from other than the outdoors will only increase your infiltration rates and make your heat loss greater . Seal the mechanical room from the rest of the house and bring your combustion air in from outside .

If sealing up the house you may at some point find yourself with a heating system that is Grossly oversized and I do mean system , boiler and rads .

I strongly suggest you contact Nate at http://energysmartohio.com/
and discuss with him . He has built quite a business model for himself in your area .

Good luck .

captainco

The amount of combustion air required for equipment has been overstated since the beginning of time. Field Controls Fan-in-the-Can is based on old assumptions of 50 cu.ft. per 1000 btus.

An atmospheric appliance with a drafthood needs 30 cu.ft per 1000, not 50. This also assumes your room is airtight with zero leakage, so even 30 cu.ft might be excessive.

I would think the CAS-5 would be adequate and most likely overkill. Usually there should be a relief damper(barometric) installed inside on the pipe from outside. This mixes inside air with outside air when 100% outside air is not needed.

The problem with combustion air is not how much you provide, but how is it going to be drawn into the equipment. Draft in the flue is the main force that draws and controls combustion air to appliances. A draft measurement in the flue determines if the combustion air is adequate and moving towards the appliance. However it does not mean it is getting to the burner. Only a combustion test can verify that. For draft to actually draw air into the burners and control it, the flue must be connected to the appliance. Drafthoods are designed to disconnect the appliance from the flue and draft. Kind of stupid but everyone still does it because that's the way it always been done. It is also the reason millions of consumers get poisoned every year and thousands die.

You need to find a contractor that knows combustion and preferably is certified. Too much combustion air can prevent a drafthood appliance from venting.

Jack

Suggest you look at the Tjernlund units as well.
http://www.tjernlund.com/combustionairintake.htm
Tjernlund also makes modulating Combustion air for commercial equipment, but yo are getting into serious gear at that point.

Frank_the_Tank

Thanks for everyone's perspective. I've signed up for an energy assessment through my natural gas supplier and should be getting someone out to perform an energy audit in the coming months. Hopefully some of the ideas presented here will be covered through the rebate program.

As a stopgap, I've taped open an old dryer vent in the basement and knocked out a window pane and installed another one. There's a rather strong draft of air coming through both of these when the boiler is firing. I've also put a brand new CO detector in the boiler room and haven't seen it go above 0 PPM.

I have my steam tech coming out later this month to replace some leaking wet returns under the home warranty and to re-work the ends of the mains to allow for some massive main and return line venting. He's also going to perform a combustion test. I had a combustion test performed in September during a tune-up and it came back as: O2: 6.7, CO: 2, and T-stack: 345. Granted, this was on a 70F day and pretty sure the basement door was wide open.

Would love to hear from anyone else that has found themselves in a similar situation. Regardless, I'll be sure to post the results of any work I do on this thread to preserve it for all of prosperity.