Boiler makeup air question

LarryK

I recently bought an old house with a one-pipe system. It has a 187K input BTU Utica boiler and I installed an Ecobee 3 thermostat. I can go online and see the see the behavior of the system on a graph. I see that every time the boiler comes on the temperature in the house drops 1 degree before it starts to climb up. I'm pretty this is because the boiler is sucking cold air into the house through all the leaky floors and walls. At least I'm not starving the boiler for air!

So I would like to provide outside air straight to the boiler. What's the best way to do this? The boiler is open to the basement, not enclosed in a room. Can I run a duct to the burners? Can I add a fan to make less pressure differential between the basement and the rest of the house? Are there any hazards to worry about?

SWEI

Maybe, yes, and yes. It depends on the layout of the basement. Is it a walk-out?

Robert O'Connor_12

Get a Fan-In-A-Can!
Tjernlund makes a nice combustion air fan. One that you can interlock with boiler. Will only come on when calling for heat.

Robert O'Connor/NJ

aircooled81

Any chance the delay in the stat calling for heat, and the time it takes to generate heat, allows for the temp to drop that 1 degree before the radiant load starts to satisfy?

Chris_L

@Hatterasguy, while I think your larger point is correct, I think you are confusing oxygen with air. Assuming natural gas is all methane, it would take twice the volume of oxygen to fully combust it (2 O2 + CH4 -> CO2 + 2 H2O). Since air is about 20% oxygen, figure about 10 times as much air as gas. Still a lot less than the natural infiltration of an old house.

@LarryK, I've used a number of digital thermostats and some behave like yours and some don't. I think it has more to do with the "stickness" of the electronics and programming than anything. My current thermostat comes on when the temp falls 1/2 degree below the setpoint, but may drop to a full degree below before the room temp starts rising on very cold days.

I don't know about the Ecobee 3, but if it has a setting for the temperature swing, try reducing it so the boiler comes on closer to the set point and see what happens.

JUGHNE

So if you were at home watching the TV and the T-stat called for heat without you knowing it would you feel uncomfortable because of the 1 degree drop if you didn't watch the thermometer?
The t-stat is doing its job by starting the heat as temp drops......would you know about the extra drop without monitoring it?
I doubt the cold outside air drawn into the basement would find its way upstairs that quickly. IMO

captainco

A cubic foot of gas or 1000 btuh needs 15 cubic feet of air. If there is a drafthood then another 15 cubic feet of air is needed for dilution air. That gives us 30 cubic feet of air per 1000 or 30 times 187 equals 5610 cubic feet of air per hour. That comes down to 93.5 cubic feet per minute which is hardly going to make a difference in house temperature.

How many degrees does the temperature in the house drop before the T-stat calls for heat.

Running a duct in the basement to outside creates more leakage, even when the boiler is not running. Sometimes we need it and sometimes we don't. Most the time everyone is just guessing.

LarryK

I think I figured out the problem. The thermostat is positioned in a hall between the leakiest part of the floor above the basement and and leaky back door. So it is a real effect but it is localized to an area of maybe 80 sq. ft. where the air being sucked in through the door seal mixes with the room air. Other sensors that are not in this area don't show the effect. I need to replace the door and put a storm door on it, I already have been planning to do that. Thanks for the help in understanding the air needs of the burner.

SWEI

A properly trained tech with a combustion analyzer would be a really good idea.

LarryK

I'll invest in that when I put in the two stage gas valve.

Tim P._3

If indoor air is used, code requires 50 cu.ft. per 1000 BTU. If the basement is wide open and you have 9350 cu.ft. down there then you are good to go. Otherwise you would need an opening to the first floor of 2 sq.in. per 1000 BTU, or 374 sq.in.

In the case of an unrated grill (one where the Ak is unknown) free air is assumed at 50%. So roughly a 30x30 grill. If you know the Ak you could probably go 24x24.

And yes, it sounds like there is a lot of infiltration, so in a completely measured and calculated world you probably don't need that much. But if you were just going to follow the code, that's the answer.

MikeL_2

Is there a difference between make up air and combustion air.............

RJ_4

Do you have the option of putting up some stud walls and sheet rock and creating a boiler room, than duct in comb/fresh air. Check local codes, may create a warmer house

SWEI

MikeL said:

Is there a difference between make up air and combustion air.

Yes.

RJ said:

Do you have the option of putting up some stud walls and sheet rock and creating a boiler room, than duct in comb/fresh air. Check local codes, may create a warmer house

First make sure that the boiler actually needs combustion air. Combustion analysis is the only way to do this.

LarryK

About the setpoint. I can see from the graph that the temp dips after the gas starts burning, it's a sharp noticeable dip on the graph but I'm sure I've never noticed it sitting in the room. I have the thermostat set for 15 min minimum burn. I also installed a Vaporstat to trip off at 8 oz. I would make it less but the differential on the Vaporstat doesn't allow it to com back on if I set it lower. The basement is about half the size it needs to be according to Tim P. But the floor is so porous I'm pretty sure it provides all the additional opening needed. But suppose I want to supply combustion air directly to the boiler and not suck previously heated air into the basement. Could I get a Field Controls CAS-4 "Fan in a Can"?

captainco

The simplest way to determine if you need combustion air is to do a draft test. If the draft in the flue is -.02" or higher when the boiler is running, you have plenty of combustion air getting to the boiler. If the draft is less, then combustion air isn't getting to the boiler. It doesn't mean there isn't combustion air in the room, it just isn't getting to the boiler but it is being pulled in another direction.

In class I discuss a job where a water heater isn't venting in an open basement. The basement and a two car garage (used for a workshop) was plenty big. However the house leakage was so great it was using the water heater flue for make-up air. this was a CO complaint call. There were no combustion air openings to the outside in the basement except what leaked through the garage door. The local tech rep for the furnace that had just been installed(2-pipe 90+) suggested some be added. He wondered in a 6" pipe would be adequate. Rather than knocking some holes in the wall to experiment, I suggested we open the garage door to see how big a combustion air pipe or grille was needed. It was a double garage door 20' X 6'. Opening it 1' X 20' did not have any effect. Or did 2', 3' or 4'. But when the garage door was open 5' the flue started to vent with a -'06"w.c. draft. I intentional didn't say the water heater vented because a draft test cannot verify venting!!!

What would have happened if someone had knocked a hole in the wall and ran a 6" pipe? A mad homeowner would have been even madder!

Draft proves or disproves adequate combustion air. Combustion analysis verifies venting.

LarryK

Come to think of it, the spill switch has been removed from the hot water heater next to the boiler.

captainco

Remember that CO poisoning is an exclusion on life insurance policies and is not considered accidental death, so no doubling up.
Didn't know water heaters came with spill switches? Unless it is at the burner?

LarryK

There is a wire on the water heater from the burner to the draft hood with nothing connected, I assume it's a spill switch but I'll investigate more thoroughly next time I'm there and look up the owners manual. I'm suspecting the boiler draft is causing the water heater to back draft as you described in your story. They are on different flues in the same chimney.

But don't worry, I'm going to get this fixed.

captainco

Sounds like a situation where many things will be done and none of them work. This is probably a non conventional (to most) repair. Without a draft test and a combustion test you could spend hundreds of dollars and not solve a thing. When I was available to go in the field this is usually when contractors finally gave up and said okay damn you, you figure it out.

If I have seen your problem once I have seen it hundreds of time and each one has its own uniqueness.

LarryK

captainco, I remembered that our paintbooth at work has a Dwyer manometer on it so I borrowed that over the weekend and measured the pressure in the flue after the draft hood and got -.07" I took a 1/8" metal tube and connected it to the manometer by a plastic tube. I inserted the metal tube up into the flue pipe through the draft hood. Maybe it would be more accurate to put the tube in a hole drilled into the side of the flue pipe? Anyway I seem to have plenty of draft. Opening doors and windows to the outside made no change in the draft pressure but it did seem like I could feel a flow of cool air when I opened the door to the outside.

I wonder how much excess air the draft hood is sucking up?

captainco

Thank goodness you checked the draft. You have combustion air out the Wazzoo! You also have a very good flue. Think what would happen if you attached outside air directly to the burner. Even in the off-cycle you would be drawing that cold air across the heat exchanger and cooling it off.

When you have a drafthood and high draft you can have lots of problems. Excessive dilution air can take up too much space in the flue and then there is not enough room for all the combustion gases which means they can spill out the bottom.

Timmie knows my position on this situation and maybe he wants to chime in.

LarryK

My wife has a sage stick she got to light and wave smoke in the cardinal directions to purge the house of evil spirits. Maybe I should light it and check the flue for evil spirits coming out of the draft hood.

Seriously, when I feel around the bottom of the hood I feel warmth but it could be radiation off the warm top of the hood. If I put my hand up inside it far enough I can feel the hot gasses making a beeline for the flue. Another paint booth item we have is a "Vanometer" to check airflow. I can bring that up and see what airflow there is around the hood. It's kind of qualitative but it's very sensitive. It only works for horizontal flow, though.

The chimney is brick. I'm sure the original installation was coal. The main wraps all around the basement in two loops. There is still a gas jet in the basement left from the original illumination system (not hooked up to anything). The inspector told me I should get the chimney lined and it's on the list of things to do.

SWEI

Replace the draft hood with a double-acting barometric and you have a far better chance of getting reliable combustion numbers.

captainco

Lining the chimney would be a big waste of money unless its has lots of cracks and holes. Not sure why people believe things will move through smaller holes better than big ones.

SWEI is basically saying what I didn't. Control draft with a barometric and then you control combustion air and venting. Also a safety spill switch can be added to assure shut-down in case of a problem. Right now if you chimney plugs the boiler will keep running until someone comes in and turns it off. Of course that would be after they take your bodies to the undertaker.

LarryK

The boiler has a draft hood spill switch already and I think there may be one by the burner, too. The draft hood is part of the listed assembly.

I'm glad to hear I don't need to line the chimney. I suspect it's like replacement windows, everyone does it because everyone knows you should even thought the actual economics don't justify it.

Anyway draft does not seem to be a problem. Just for kicks I should check the draft pressure inside the boiler upstream of the hood and get -.02" there, right?

captainco

By definition and function a drafthood is designed to prevent draft from pulling the flue gases out of the equipment. It is to keep pilots from blowing out, allow equipment to operate with a plugged flue, and prevent the draft from pulling by-products of combustion from the equipment. There is almost never a measureable draft below a drafthood.

Even though the drafthood disconnects equipment from the chimney, every time draft changes, the amount of combustion air going into the burner and the amount of flue gases exiting is changing. Dilution air from drafthoods is a major cause of flues condensing and deteriorating.

The drafthood is a listed part of the equipment but the hole in it isn't, so we block it and add a barometric instead. Barometrics control combustion air to the burner and the venting of flue gases consistently. The combustion process requires two things to be controlled: fuel and air. Somehow our industry only believes that fuel should be controlled and air should fend for itself.

A field test I did with AGA in 1993 validated that a barometric was a viable alternative to the factory supplied drafthood and made equipment safer on 100% of 18 appliances we tested and modified. In 1994 AGA stopped certifying equipment and now CGA does it. Hmmmm?

If one checks the Consumer Products Safety Commission recall list for the last 15 years, drafthood equipment leads the list for heating devices. Of course they call the hole in the drafthood a CO leak.

Normally a drafthood would require at least three spill switches to be safe whether it was built in or round on top. Barometric only spill in one place so they only need one. Because barometrics actually control venting, spilling rarely occurs.

If I had a dollar for every drafthood appliance I helped contractors convert to barometrics and solve problems I might be typing this from an island in the Pacific.

Mark Eatherton

I've had ONE (count it on one finger, you pick the finger) job where a barometric DIDN'T correct all ills. I wrote an article on that near death experience... 500K btuH copper fin tube snow/ice melt boiler, in a basement mechanical room (isolated, unheated mechanical room with code approved combustion air). The mechanical room was un heated, important point. The 18" stack was 3.5 stories tall.

When the boiler would go to fire for a ice/snow melt call, under the right conditions, the stack could not achieve draft, so the appliance would spill, fill the room with CO2, snuff the burner,and it (CSD1 compliant) control would lock the boiler out. By the time we'd get there, and reset the system, it was warmer and it would take off and work as it was supposed to.

In an effort to resolve, we blocked the draft hood, installed a barometric damper with spill switches (top and bottom of the unlisted hole). Problem persisted. I told the consumer, that the next time it happened, that regardless of the time of day, I wanted a call so I could observe what was going on in real time. I got the call at 3:00 AM. By the time I got there, the lady of the house was suffering from CO exposure. I smelled aldehydes as soon as I walked into the house. I confirmed my suspicions when she offered me a cup of coffee, and asked me if I wanted cream, to which I replied in the affirmative. She poured me a cup of cream and a splash of coffee....

Fortunately, none of her kids were home (college). I sent her to her car and told her to pull it out of the garage, and stay warm while I diagnosed. What I saw when I reset the boiler caused the hair to stand up on my neck. The boiler was spilling from the combustion chamber, not the barometric damper. It was a white fog that just poured out of the combustion chamber. It rolled out so bad that it actually melted the wiring going to the main gas valve, which shut the boiler off. I don't think that is a code approved spill switch, but it was very effective. Took the main transformer out.

I posted about it here on the wall, and got tons of flack for exposing myself to the CO potential, but I had no choice in the matter, and I took some personal precautions to limit my exposure (head stuck in the combustion air pipe while observing the situation). There is a threshold (399K btuH) that spill switches are no longer required. I guess the people who put this standard together decided that these commercial products never spill, and or they don't deserve the same protection that smaller boilers do...

To resolve her case, we ended up having to replace the boiler with a sealed combustion mod con boiler. The lady could have afforded to burn cash on the driveway for snow melt if it weren't for the smoke and the fly ash. She has no idea how close she came to meeting her maker. Her bedroom was directly above the offending mechanical room.

So, I guess what I am trying to say here is that what happens on the "test bench" rarely emulates what happens in the field, and as Jim has pointed out NUMEROUS times, the best fix is the proper installation AND ADJUSTMENT of a barometric damper, but even in those situations, you need to be aware of ALL operating parameters (cold start mechanical room with 35 feet of cold slugged stack that wouldn't/couldn't overcome cold air plug). FWIW, I've also observed improperly adjusted barometric dampers that were wasting significant amounts of energy (over weighted damper)

On an even stranger note, I had a friend for whom I had acquired a used 50,000 cast iron boiler. He and an allegedly qualified friend installed it, along with a bunch of other hydronic equipment. He asked me to come review the install before he moved in. They had somehow lost the atmospheric draft hood, and his friend didn't think it was necessary. they plugged the exhaust directly into an internally located brick chimney. Directly below the entrance into the chimney, there was another 3" hole in the chimney that was screened off. I know not what it's intended use was, but it was acting as draft relief for the appliance. This boiler had THE most perfect combustion numbers I had ever seen for an atmospheric appliance. no excess air, no CO, and perfect stoichiometric numbers. It was a temporary heat source, so I didn't force him to put in the baro with spill switches, but did have them install an audible CO detector in the mechanical room. It lasted for one year with no other issues. It too was replaced with a modcon.

Just when you think you've seen it all....

As it pertains to "carbon monoxide leaks", that makes the hair on my neck stand up every time I hear it. I realize that firemen are not supposed to be experts, but they shouldn't be making such determinations without having gotten properly qualified.

I think it should be mandatory that all fire departments take Jim's class. I aslo wish that he had gotten one dollar for each barometric damper that was installed by his teachings, and also wish he had a secluded isalnd wher I could go visit him in the winter

Be safe out there. Great thread.

ME

SWEI

Mark Eatherton said:

I realize that firemen are not supposed to be experts, but they shouldn't be making such determinations without having gotten properly qualified.

I think it should be mandatory that all fire departments take Jim's class.

I can not overstate the value of the class for anyone in this industry.

I've been speaking with my local fire marshal about CO and am now thinking that a half-day class for first responders might be worth pursuing. They don't need to know how to fix appliances, but they do need to better understand potential risks and causes.

captainco

Mark,

Just had another good company run across a similar sort of situation. Put a barometric on a boiler and it performed fine until some furnaces that heated another part of the building were turned on. They had severe duct leakage and caused the boiler to vent out of the bottom and fortunately melted some wiring also and shut it down.

I can say I have been on at least a dozen cases where a barometric alone did not solve a problem. In all cases it was because of severe depressurization, whether in a house, a plant or a restaurant. The key to the final solution was could the mechanical room be pressurized? Sometimes it is as simple as getting rid of the combustion air openings that are sucking out instead on in. But when it is just building leakage or competing exhausting appliances, the mechanical room can't be pressurized. Therefore when you can't blow combustion air to equipment you will have to suck it. That means put a draft fan in the flue above the barometric. You still need the barometric or it won't be connected to the flue or fan.

A draft test and draft interference test are critical on every vented appliance. We have a zero tolerance for any reduction in draft, even 1 pascal (.004"wc) when any changes are made to the internal environment, which in some cases may just be opening or closing a certain door. We are never present during the so called "Worst Case Senario"!! In fact in most cases it is the "Least Case".

I learned a long time ago, don't get overly impressed with myself or I will screw up royally. Every day is a new day and every job is a new set of conditions where few assumptions should be made. Measuring is the only thing that will keep our butts out of trouble.

Thanks for the reminder Mark!