Firetube vs Watertube Used Boilers: What Buyers Should Know

Used boilers come in two basic designs, and the design determines what the boiler is good for, how it fails, and what a buyer should look at before paying for it. Most commercial and light industrial buyers end up with a firetube. Process plants with high pressure or high capacity needs end up with a watertube. Here is how to tell which one you need and what to check on each.

How they differ

In a firetube boiler, hot combustion gases pass through tubes surrounded by water inside a pressure vessel. The shell holds the water, and the tubes run through it. Firetubes are compact, forgiving, and hold a large volume of water, which makes them stable under swinging loads. They are the standard for heating, domestic hot water, and low- to moderate-pressure process steam.

In a watertube boiler, water runs through the tubes and the combustion gases pass around them. The design allows much higher pressures and capacities, responds quickly to load changes, and is the norm for large process steam, utility, and high-pressure applications. Watertubes are larger, more complex, and more demanding to operate.

Which one is on the used market

Firetube boilers are the bulk of what comes through the used market: packaged Scotch marine units from hospitals, schools, laundries, hotels, and light industrial plants. They are in every size range and, because they are packaged with the burner and controls, they are relatively easy to move and reinstall.

Used watertube boilers come from process plants, food and beverage facilities, and industrial closures. They are less common, tend to be larger, and often require disassembly to move. A buyer looking at a used watertube should have a specific process reason for needing one.

What fails on a firetube

Tube ends and tube sheets are the wear points. Look for evidence of tube leaks, rolled or replaced tubes, and corrosion at the tube sheet from poor water treatment. Check the refractory in the rear door and furnace for cracking. Look at the shell around the handholes and manways for pitting. Ask for the last internal inspection report; a firetube that has had its tubes inspected and passed is a much safer buy.

The burner and controls matter as much as the vessel. A packaged firetube with a modern burner and a working control system is worth considerably more than the same vessel with an obsolete burner that will need replacing.

What fails on a watertube

Tube condition throughout, and particularly in the furnace section where heat flux is highest. Drum internals. Refractory and casing. Superheater condition if the unit has one. Watertube inspection is more involved and the buyer should plan on having someone qualified look at it. Water treatment history is even more important on a watertube because scale in a high-flux tube causes overheating and failure.

Pressure vessel records

Whatever the design, a used boiler is a pressure vessel, and it will need to be inspected and certified for the jurisdiction where it is going to be installed. A unit with a legible nameplate, a national board number, and a recent inspection history is far easier to get certified than one without. Ask for the records before negotiating on price. The wider inspection process is in inspecting a used industrial boiler before you buy.

Sizing

Know your load in pounds of steam per hour or BTU output, your required pressure, and your fuel before you shop. A firetube that is oversized for the load will short-cycle and waste fuel. A watertube bought for a load a firetube could handle is more boiler than the site needs to operate and maintain. If the application is heating or moderate process steam, a firetube is almost always the right answer.

Frequently Asked Questions

Which is more common used?

Firetube, by a wide margin. Packaged firetube boilers are what most commercial and light industrial buildings use and what most often comes out of them.

Can a used watertube be moved in one piece?

Smaller packaged watertubes, yes. Larger units are disassembled and re-erected, which adds significant cost.

What is the single most important document?

The most recent inspection report. It tells you the condition of the tubes and vessel and whether the unit can be certified where you are installing it.

Do you have used boilers available?

Yes. We buy used boilers from closing facilities across Florida and nationwide, and current units are at used boilers for sale.

Demo Dynasty buys and sells used industrial boilers from Auburndale, FL. Call (689) 323-4676 or contact us about a specific unit.