Combustion air for a boiler...finishing a basement

FloMo201

Hello everyone,

We are going to begin a basement finishing project soon. While discussing with our contractor, he told us that we should have our HVAC person ensure the boiler and hot water heater will get enough air for proper combustion since permanent walls are being put up and the size of what he called the mechanical room is going to be significantly smaller.

Did some googling, and I understand what he is telling me. The boiler and hot water heater will be in a significantly smaller place as the unfinished section is being greatly reduced.

These hot water heater and boiler are both natural gas. Hot water heater is a Rheem and the boiler is a Peerless MI-e. I will get my HVAC guy involved in the project. What should I know so that when I discuss with him, I am somewhat educated.

Thank you, Flo

Robert O'Brien

"A confined space is defined by NFPA 54 as a room containing one or more combustion appliances that has less than 50 cubic feet of volume for every 1000 BTUH of appliance input.

For confined spaces, the NFPA 54 requires additional combus­tion air from outside the CAZ. Combustion air is supplied to the combustion appliance in four ways.

1. To an un-confined space through leaks in the building.

2. To a confined space through an intentional opening or openings between the CAZ and other indoor areas where air leaks replenish combustion air.

3. To a confined space through an intentional opening or openings between the CAZ and outdoors or ventilated intermediate zones like attics and crawl spaces.

4. Directly from the outdoors to the appliance. Appliances with direct combustion air supply are called sealed-combustion or direct vent appliances."

JUGHNE

The boiler and WH nameplates will tell you the btuh INPUTS.

Add those up and go from there.

Often a fully louvered door into the boiler room will suffice.

hot_rod

If you do pull from another space, be sure you have enough 'leakage" to assure adequate oxygen to the burners.
I had a case where two people died in a home after they plugged off all the air inlets and had a boiler and wood stove running. This wasn't even a super tight construction home, built in the 1980's.

A blower door test would spell out how much leakage you have. Good idea for energy upgrading also.
If it is easy to access I would bring in a % of outside air.

Working in a cold mountain climate our AHR allowed us to cut down the outside air to 1/4" per thousand BTU a high and low combustion air grill.

As always a good quality low level CO detector should be installed near the "boiler room".

EdTheHeaterMan

I have to complement your contractor for his recommendation. I have personally experienced a job completed by a so-called "Professional Contractor'' that put a 6-12 pitch roof over a flat roof for my father. We needed to call the paramedics for the insulation crew after working in the newly made "ATTIC" because the oil burner chimney vented into the newly made "ATTIC". When asked why the chimney was not extended thru the new roof, the contractor said that he was planning on doing it next week after the insulators were finished.

There are also many “finished basements” that were causing oil burners and gas burners to create soot for several years without the rookie HVAC tech realizing that the old unfinished basement was recently finished, causing the boiler room to become a “confined space”. Once the combustion air was provided for, the sooting problem vanished.

Good call!

FloMo201

Thank you everyone. My contractor mentioned a louvered door, but said its best to talk to the experts. Once I know what my HVAC guy recommends I will post a follow up for a sanity check.

The hot water heater is 76k btu, and the boiler if 175k btu. The unfinished section will most likely measure 15ft wide, 8ft deep, and 8ft in height. There is a crawlspace type of window near the hot water heater that we will leave.

I have CO2 (not low level) detectors on every floor of my house. Once this is done, would the CO2 detector be placed in the mechanical space, or in the finished space?

Thanks again, Flo

clammy

When making a enclosed mech room aside from make up air which if the basement is semi sealed a fan in a can should be added a louvered door for a 175 btu boiler sounds like a general contractors way of keep cost down which personally is not ensure proper combustion and safety for you and or your equipment nor your safety and proper operation of your system when it s winter and everything is closed . Not to sound like a tool you will likely not find many hvac contractors who even have a clue about combustion air you have to find some one who is familiar w combustion and codes . I known this due to being in the business and in talking w many in the business I’m always amazed at how much most do not know usually because most care about one thing and that’s making a ton load of money plain and simple , the rest of it and the work is the means for the money .
Also in closing your mechanical room be sure to leave enough room for future replacement and service other wise as nice as the finished basement is not many service or installation guys will enjoy working thought it and usually replacement cost are higher on finished basement then a non finished just goes to reason . I know I charge more for replacement on finished basement more time more drop cloths and usually less room and more cleanup .
Telling the truth reguardless of the out come peace and good luck clammy

FloMo201

Thank you all. A fan in a can? going to google that one!

Karl Reynolds

Field Controls CAS systems.

MikeL_2

   And please make sure to educate yourself on the difference between make up air & combustion air; they often compete with each other....

Bob Harper

ASHRAE did a comprehensive stufy on MUA and proved passive systems are wholly unreliable. All those holes in walls schemes rely on a negative pressure in the CAZ WRT the adjacent zone. That means it would fight draft pressure. Pressurization of the CAZ ensures natural draft but has consequences. Passive MUA drawn from outdoors is at the mercy of the wind. If the intake is located in the leeward side of the building, it can pull air out of the CAZ further exacerbating depressurization. The Field Controls Fan in a Can is a system with a good track record but there are other ways.