Barometric damper for single family home?

Yes, that's the draft hood. Any combustion test performed, the probe needs to be upstream of the hood. Pretty much right at the block.

It seems like you are not using a thermometer to measure the flue-gas temperature or the temperature of the vent connector pipe. To be clear, that pipe can normally be around 300°F or hotter while the boiler is operating.

For comparison, put your hand under running water at 120°F and that is already about as hot as most people can comfortably tolerate. At much higher temperatures, serious burns can occur very quickly. 160° water can cause second degree burns almost instantly

So, if you are using your hand to judge the temperature of a pipe that may normally be around 300°F, your hand is not a very good measuring instrument. At that temperature, "too hot to touch" is exactly what I would expect.

Now consider how the boiler works. There is a flame that can be around 2,000°F or hotter at the bottom of that cast-iron boiler. The purpose of that flame is to heat the water until it boils and becomes steam.

At atmospheric pressure at sea level, water boils at about 212°F. A residential steam boiler operating at a small amount of pressure will boil the water at a slightly higher temperature.

In order to maintain boiling water on the inside of that cast iron, the combustion gases traveling across the other side must obviously be considerably hotter than the water. By the time those gases have transferred much of their heat to the boiler and reach the flue outlet, temperatures around 300°F or higher are not unusual.

So the fact that the vent pipe is far too hot to touch does not, by itself, indicate that something is wrong. Measure the temperature with an instrument rather than your hand. Then you have an actual number that can be compared with what is normal for that particular boiler.

I'm not sure if this boiler image is from your boiler's manual, but your boiler is close to what is shown in this illustration.

I have indicated the blue/yellow flame at approximately 2,000°F. The water in the boiler absorbs about 80% of the heat produced by that flame. The flue gases leaving the top of the boiler may be around 400°F. When those gases reach the draft hood, they mix with cooler boiler-room air. We call that dilution air, and it can lower the temperature of the gases entering the vent connector to around 300°F.

These numbers are estimates, and the actual temperatures of your boiler may vary.

Some additional information about the vent damper: You indicated that there is a nickel-sized hole in the damper blade. That hole is there for a boiler with a standing pilot, so that when the damper is closed, there is still an opening for the pilot burner's combustion gases to vent up the chimney.

Since your boiler has electronic ignition, you can plug that hole. There is a special plug made specifically for that purpose.

There are really two very different things going on here — though they are related. The first is combustion air flow through the boiler. The rate of that flow must be kept in the correct ratio to the gas flow for complete combustion to take place. That balance — in a natural draught boiler such as yours — is set by the geometry of the air openings at the bottom, for the intake air, by the geometry of the passages in the boiler, and by the geometry of the exhaust opening at the top of the boiler.

But — there is a potential problem. As @EdTheHeaterMan pointed out, that exhaust gas is warm — in a steam boiler, it has to be, as otherwise there would be no heat transfer to the boiler metal and thence to the water to make steam. If the boiler were sitting out in the open — say in your backyard (I don't recommend that!) that wouldn't be a problem — but it isn't. It's connected to some kind of chimney or flue, of necessity. Now if that hot gas were allowed to go into the flue all by itself, it would cause a considerable draught which sounds desirable, but isn't — as it would upset the air flow through the boiler. Which, remember, has to carefully arranged for proper combustion. By far the simplest arrangement, which works perfectly for an atmospheric boiler, is to allow ample air in by the draught hood. This does two things: it stabilises the air pressure at the outlet to the boiler, ensuring correct air flow through the boiler, and incidentally reduces the temperature of the gas going up the flue — which reduces the wear and tear on the flue.

A barometric damper on the flue does very much the same thing, but is used for boilers fitted with a power burner (one with a combustion air fan). In all honesty, it isn't quite as good a solution, as unless it is very carefully calibrated and is working with an equally carefully calibrated fixed damper on the exhaust from the boiler, the air flow will not be as well stabilised.

Now you mention a concern about the industry not making a serious effort to increase the efficiency of residential steam boilers. Not true. As I noted above, the size of the openings is very carefully adjusted to achieve correct combustion, and the actual thermodynamic efficiency of the boiler itself, in any reasonably modern boiler, will be right around the theoretical maximum for the fuel — provided the air/fuel ratio remains carefully adjusted. Although the temperature of the exhaust gas is high, there is actually very little heat there to be recovered.

Note carefully here that if there is a way to reduce that exhaust gas temperature into the range where the water vapouur of combustion can be condensed, that efficiency can be increased — for gas perhaps as much as 10% (for oil it is less — but the inherent efficiency of oil is greater to begin with). But — that is impossible with normal steam heat, as by definition a steam boiler is running above that temperature.

If the natural stack draught is very high, some installations use a flue damper which is closed when the burner is off and opens when the burner is on. I personally am not particularly keen on these — particularly for atmospheric boilers, as they eliminate any most of the possible post-purge of the residual combustion gas in the boiler (they are a little more practical for power burners, as those are almost always set up with a pre-purge and post-purge to do just that.

You imply that you are running a vacuum steam system. In such a system you can, of course, recover some of the heat remaining in the boiler when the burner shuts off. However, it is essential to still ensure that residual combustion gas is evacuated from the house. For this reason the best practice for vacuum steam is either a power burner and powered flue damper, as mentioned, or for an atmospheric boiler a damper on the intake opening, again powered and interlocked so gas cannot flow unless it is fully open. In this way any residual gas which is inclined to escape will still be removed by the flue, but airflow through the boiler will be reduced.

Here let me refer back to the comment above on "condensing range". It is tempting to suppose that a steam boiler can be run in that range — but this requires a very deep vacuum (around 25 inches of vacuum) which is remarkably difficult to obtain, never mind sustain.

@pacoit , you'll want to have a pro check the firing rate and do a combustion test. If the stack temp is too high, the burners may be over-fired. This can also cause high CO.

How did you "turn down the gas valve"?

Did you do a combustion test?

@pacoit commented: "I still wonder about the purpose of the draft hood opening, especially as big and unrestricted as it is. Isn't the air coming up from under the boiler enough? Is there some special airflow dynamics/requirements that would explain it?"

The draft hood acts as a hydraulic separator for air: it disconnects chimney draft from the combustion chamber, supplies dilution air, stabilizes burner operation, and provides a relief opening if the chimney cannot draft properly. All that in one big opening. There are other boilers that have no draft hood built in, so you add one after the boiler vent opening, like this.

Observe the draft hood on the boiler on the left. With the draft hood, the boiler is not directly connected to the chimney. That is the hydraulic separation. The flame can burn at its regular rate at atmospheric pressure, supplying air just like the burner on your kitchen stove.

There are no other forces acting on the amount of air going through the primary air opening or the secondary air opening, so the flame can get as hot as it can with the normal amount of excess air needed for proper combustion. No more, no less combustion air.

Now look at the boiler on the right. There is no separation between the boiler exhaust and the chimney. So, on a day when conditions allow the chimney to produce a lot of draft, such as a cold, crisp winter day, that chimney can act almost like a vacuum cleaner, pulling a lot of air from inside the house through the boiler and up the chimney.

Now, when you need the heating system to be the most efficient, that strong chimney draft is directly connected to the boiler. It can pull additional air through the combustion chamber, increasing the amount of excess air entering at the bottom of the boiler. For illustration, let’s say that additional excess air lowers the flame temperature from around 2,000°F to perhaps 1,800°F.

Since a greater volume of air and combustion gas is now moving through the boiler, the hot gases move through the heat exchanger faster and have less time to transfer their heat into the boiler water. Instead of leaving the boiler at perhaps 400°F, the exhaust temperature might now be over 500°F. That is heat you paid for going up the chimney. Excess airflow through a heating appliance increases stack losses and reduces efficiency. So you are starting with an 1800° flame with a 500°+ exhaust. that makes the efficiency drop from 80% to below 70%.

There is also no draft-hood dilution air being introduced at the boiler outlet. Dilution air would normally reduce the temperature and lower the dew point of the gases entering the chimney. Without that dilution, the chimney is exposed to hotter, more concentrated flue gases. Depending on chimney construction and operating conditions, that can place additional thermal and moisture stress on the chimney and liner.

The end result is that excessive chimney draft can pull more air through the boiler, move the combustion gases through the heat exchanger faster, send more usable heat up the chimney, and reduce the overall efficiency of the heating system.

This is oversimplified and there is a lot more going on here, but it covers the basics. The actual temperatures may be different and are only used to make the point about the need for that big opening under the exhaust pipe to the chimney for your steam boiler. You could hire someone to make a sheet metal cover to seal in all the heat, but you may end up with an increased gas bill. Someone smarter that you and I designed that boiler you have in your basement and you are wise to keep their design just the way they made it.

Hope this helps.

The manual gas valve on your boiler should be 100% open. You can't regulate gas pressure or BTU's that way. Its dangerous. That valve is there for emergencies, or when a tech is working on it. The ELECTRONIC gas valve has its OWN regulator. The gas valve is checked and the regulator adjusted if needed by the tech. Open it.

I believe you still have an atmospheric boiler. Can you post a picture?

Yeah, that's not good. The gas shutoff valve — which you are playing with — is for service or emergencies only. the regulator on the burner is what needs adjusting, and clearly that hasn't happened. That adjustment is done with instruments which actually meausres how good — or not — combuston is. You need a tcch. to come and adjust your burner to fire properly…

Your boiler, from the pictures and your description, is a natural draught atmospheric boiler. It is intended to operate with the draught hood. Adding a barometric dampler may not hurt much, if there is adequate draght in the chimeney, but it wouldn't accomplish anything either. If you managed to kill the draught in the chimney, thogoh, the boiler would exhaust into the house… and that just isn't good.

People spend a good bit of time and effort in engineering these things to work as efficiently as possible — and safely.

Two bad ideas

The barometric draft regulator is not the better design for an atmospheric burner. A barometric regulator is designed primarily for a power burner. That type of burner uses a fan or blower to provide the combustion air. Adjustments control the amount of air and fuel being mixed by the burner before that mixture enters the combustion chamber, where the actual flame is produced.

With a power burner, the combustion chamber may be operating under positive pressure near the burner. At the same time, chimney draft creates negative pressure through the boiler's heat exchanger and flue passages. Somewhere in that process, those forces have to reach the proper balance so the burner operates with a stable, properly adjusted flame.

If the chimney draft changes significantly, that balance can also change. That is where the barometric draft regulator comes in. It helps maintain a relatively constant draft over the fire, meaning in the combustion chamber. As the chimney pulls harder or weaker, the barometric damper opens or closes automatically in real time to compensate for those changes.

That type of device is not needed in the same way on an atmospheric burner because an atmospheric burner depends upon the atmospheric pressure of the air in the room where the burner is located. It is not using a burner blower to force a precisely controlled amount of combustion air into the combustion chamber.

Think of it like the gas burners on a cooking range. You have a burner producing a flame with a pot of water sitting above it. That burner does not need a barometric draft regulator. The combustion products from the flame rise into the kitchen and mix with the surrounding room air.

Now imagine a cooking appliance large enough that you would not want all of those combustion products and heat entering the room. To deal with that, you place an exhaust hood over the cooking equipment and vent the hood outdoors. You may already have a range hood in your own kitchen that you use when cooking a large meal with several burners and the oven operating at the same time.

Commercial kitchens use much larger versions of the same idea. They have large exhaust hoods over the cooking equipment. There are no barometric draft regulators controlling each burner underneath those hoods because the bottom of the hood is completely open to the kitchen. The burners are operating in the atmosphere of the room, and the hood collects the hot gases and carries them away.

That is essentially the principle behind an atmospheric burner. The boiler simply puts the heat to better use. Instead of using the flame to heat a pot of water on a stove, the boiler transfers that heat into water and makes steam for your radiators.

As I said before, and I want you to understand what I mean when I say it again: Someone smarter than you and I designed that boiler sitting in your basement. The burner, draft hood, flue passages, chimney connection, and combustion system were all designed to work together.

Don't try to redesign years of proven technology by changing one part of the system because another arrangement seems like it should work better. If you don't like the basic design of an atmospheric boiler, then replace it with equipment that was designed from the beginning as a sealed or power-burner system. If that system requires a barometric draft regulator, then the regulator belongs there because it is part of the engineered design—not because somebody decided to add one to an atmospheric boiler afterward.

That is not an adjustable valve. There is no accuracy in the partial closing you have decided to do. The adjustment should be made by a professional with a manometer at the gas pressure regulator, noy at a manual shut off valve. You have several of these on your home. One is at the gas meter, and another is inside the gas control at the boiler itself.

Between those two valves, a professional with experience in gas appliances can diagnose your higher gas bill and determine if your pressure is too high. If it is, and you have a gas range that you cook on, then turning on a burner to boil water will use more gas at a higher pressure than it did at a lower pressure.

Perhaps the old gas mains were insufficient for the area, and all your neighbors on that low-pressure gas main were operating their appliances at a pressure that was lower than it should have been. Perhaps the old gas meter was inaccurate. Now everything is operating properly, and you are getting the gas bill you should have had all along.

Just a question about your higher gas bill: Did it get lower after you made the gas valve adjustment? Regardless, you should have a professional check the gas pressure at each appliance and the gas pressure at the meter to see if it might be a little too high.

Can you please address the fact that you'll fully open the gas valve and get the system checked? I don't know who told you that you could do that, but you should punch them. Hard.

I have a feeling that when your gas service was upgraded, you started getting higher gas pressure at all of your appliances.

Before that, the gas pressure may have been lower than it should have been. As a result, someone may have adjusted the appliance regulators to allow the maximum available gas pressure to reach the burner orifices.

That may have been the correct adjustment when the supply pressure was low, but once the gas service was upgraded, each appliance should have been checked and readjusted to the proper gas pressure for efficient operation. Obviously, that was not done properly.

If I were in your situation, especially with the noisy operation and higher gas bill, I would have been very persistent with the gas company about correcting it.

On newer heating equipment, the proper place to adjust gas pressure is at the gas control valve, which usually includes the pressure regulator. Older systems from the 1930s through the 1960s may have separate gas valves and pressure regulators.

Regardless of the age of the equipment, the gas pressure should be adjusted at the regulator, not by partially closing the manual shutoff valve.

Another pressure-adjusting location is at the gas meter. The pressure coming from a newer gas main can be much higher—sometimes up to 60 PSI before the service regulator. On the house side of that regulator, the pressure is usually around 7" WC, which is less than 1/2 PSI on a conventional pressure gauge.

If your old gas main was only supplying 5" or 6" WC by the time it reached the meter, you may have been operating at 4" WC or less at some appliances. With the appliance regulator cranked wide open, you might still have been getting only 3.5" WC or less during periods of high neighborhood demand.

That could explain why things changed after the higher-pressure gas main was installed. Have a professional with a gas-pressure manometer and combustion analyzer check and properly adjust your boiler, water heater, and any other gas appliances.

If the gas company will not do it for free—and I think they should—pay a qualified technician to do it. That is much better than trying to compensate by partially closing the manual gas shutoff valve.