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Heating Boiler
Primer

Lets take a look at what a boiler can do for you:

• provide the power for abundant hot water for showers, laundry and dishwashing
• give you the ability to have heated floors
• heated towel racks
• snow or ice melting of sidewalks and driveways
• heat a pool or hot tub
• ability to have different temperatures in separate areas of a building

All of the above can be accomplished with a single appliance (a boiler) rather than multiple machines.

I’ve been to many homes that have as many as five appliances.

This creates a lot of maintenance issues.

It’s a lot easier and less expensive to maintain one heating boiler.

The other disadvantage of multiple machines is lower operating efficiency.

Some units operate at only 60% efficiency, while a boiler can provide efficiencies in the 83% - 95% range.

The life-cycle of some boilers can be over 30 years compared to a standard water heater that has a 9 year life expectancy.

The key to gaining these advantages is choosing the right boiler.

What to look for

One of the first decisions you’ll have to make is fuel type.

Your choices are oil boilers, natural gas boilers, propane boilers, electric boilers and wood boilers.

Factors to consider are availability and price of fuel.

Another consideration is how the heating boiler will be vented.

Some boilers are designed to use a chimney and some have a built-in venting system that expel the gases through the sidewall of a building.

Boilers that are designed to be vented with a chimney can be vented through a sidewall with an add-on device called a power venter if a chimney is not available.

Although I have used this type of venting system when there was no other choice, but I consider it the weak link of a system.

My experience has proven that they last for approximately six years before maintenance or replacement is required.

Other disadvantages are the staining of the outside wall and odor of the gases.

If oil is the fuel it can be like having a bus parked in your yard with it’s engine running, .

If you live in an existing house and are replacing an older boiler you will most likely be have to install a chimney liner.

The newer, more efficient boilers have lower flue gas temperatures that require a smaller chimney area.

Failing to install a liner can result in carbon monoxide due to poor venting as well as condensation build-up in the chimney.

This condensation eventually causes the chimney to deteriorate.

I’ve seen this happen and it’s not a pretty sight.

Efficiency ratings of heating boilers have a rating system called AFUE.

AFUE stands for Annual Fuel Utilization Efficiency.

The simple explanation of AFUE is the ratio of heat that goes into the living space vs. what is lost up the chimney.

Older heating boilers can have efficiency ratings as low as 50% while newer versions range from 83% to 95%.

In theory, if a boiler has a 90% rating, you should get 90 cents worth of heat for every dollar you pay.

Higher ratings don’t always translate into lower fuel bills.

This rating system has many shortcomings because they are based on best-case scenarios and assumptions that don’t really exist in real world applications.

Boiler construction

There are many boilers still operating that are 80 -90 years old.

Though they may not be super-efficient, they have proven to be durable and reliable because of the amount of mass (material) in the construction of these vessels. A lot of cast iron and water.

Compare these with today’s boilers that you can carry into a basement.

Some of these newer versions are made of aluminum or copper and hold only 1-2 gallons of water.

These lightweights are referred to as low-mass boilers.

At first glance this may seem a smart way to do things. I use to think so until I found the real truth.

The selling point of the manufactures of these low mass appliances point to the fact it is wasteful to heat up hundreds of pounds of water and cast iron.

This sounds reasonable and to a certain degree it’s true.

When you have all this heated mass there is the potential for the heat to be lost up the chimney and surrounding air of a cold basement.

This is the heat you pay for that never finds it’s way into your home.

The smaller, low-mass, low-water content units do not have this problem but have their own pitfalls.

A quick lesson about boilers and combustion

When a burner first turns on , the combustion process is at it’s lowest efficiency for the first 5-7 minutes.

This is no different than your car.

The first 5 minutes you drive your car is the worst in terms of gas mileage and pollution.

Once the car is warmed up, it then starts to run more efficiently.

This is called steady-state efficiency.

A boiler operates in the same way.

One of the problems of low-mass, low-water content boilers is that most times they will only run for 2-3 minutes and never get a chance to reach steady-state efficiency.

This is called short-cycling.

When I spoke about AFUE ratings not being real-world, this is one of the things that is not accounted for in their ratings.

Low mass systems can cycle on and off over 30,000 times in a season causing wear and tear on controls.

The older large mass, high water content boilers have long run cycles enabling them to reach steady-state efficiency.

Regarding longevity and durability it just makes sense there would be less stress on a large mass vs. a low mass when the same amount of heat is applied.

Low-mass construction is mostly found in gas boilers while most modern oil boilers are constructed of either cast iron or steel and have a water content of at least 3 gallons, depending on the heating capacity of the boiler.

Some boilers are constructed of aluminum, but the ones constructed of cast iron or high grade stainless steel are the best bet for longevity.

A well respected German manufacturer discontinued the use of aluminum because of the question of longevity.

The smart manufacturers learned what it takes to overcome the shortfalls of both the high and low mass approaches.

As previously stated, the problem with large water content is the unwanted heat loss when the boiler is idle (no demand for heat).

Simply adding more insulation to the boiler will keep most of the heat in the boiler.

Reducing the water temperature in the boiler also reduces heat loss. (I’ll discuss this strategy in the controls section of this page).

Short cycling of low mass units is greatly reduced with the introduction of modulating burners.

A modulating burner adjusts it’s firing rate to the demand for heat.

It’s like stepping on the gas in your car when you need more power.

Some manufacturers do a better job than others to ensure that combustion efficiency remains high during the higher and lower firing rates.

Boiler Control

The control system is a major factor to actual energy savings.

The typical heating cycle of a hot water system consists of 180-200 degree water circulated through a radiator or baseboard system.

Unless it is the coldest day of the year, these high water temperatures are unnecessary.

Believe it or not, at certain outdoor temperatures you can actually heat a home with 80 degree water temperatures.

Control systems are now available that adjust the water temperature according to the outdoor temperature.

As the outdoor temperature drops the boiler temperature increases.

This is referred to as weather responsive control or outdoor reset.

Energy savings of up to 20% can be realized using this common-sense strategy if it is applied to the right boiler.

Most boilers, especially oil-fired and mid-efficiency gas boilers cannot operate at lower water temperatures because of the risk of oxidation in the boiler, decreasing the life of the unit, these units are not able to take advantage of the full range of a weather responsive control.

On the other hand, high efficiency gas condensing boilers with AFUE ratings over 90% are a perfect match for low water temperatures.

The cooler the water, the more efficient the boiler.

High quality, high efficient boiler systems can cost up to twice as much as others, but you’ll recoup your investment through lower energy bills, less repairs and a longer lasting system.

Please realize you are not just buying a boiler.

You are buying just one part of a building system, one thing affects the other.

This is called the whole house or the house is a system approach.

Now that you are armed with some knowledge of the heating boiler, the only thing left is choosing the right contractor who is in alignment with the above information.

Instead of re-inventing the wheel, use my 31 years of experience to enjoy the benefits of owning a reliable heating boiler.

Most people ask me what kind of boiler I have in my own home.

For the last 10 years I have enjoyed my German-made Viessmann boiler.

I consider it one of my better investments.


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