Bottom Blowdown – The Right Way

The sequence of valve operation in boiler blowdown is extremely important.  Despite the variety of procedures in practice, there is one, and only one, proper sequence in opening and closing the bottom blowdown valves of the boiler.

The opening sequence is to open valve B first and then valve A.  The closing sequence is to close valve A first and then valve B (Figure 1).  When this sequence of events is followed, the open space between valve A and valve B (shown as C) is always pressurized.

Recently a customer experienced a problem with their bottom blowdown valves.  A metallurgical analysis of the parts revealed severe oxygen pitting and resultant valve failure.  The cost of these failures is enormous. 

 Surprisingly enough, replacing the two valve stems and seats every six months accounts for only a portion of the cost.  More significant was the expense incurred by shutting down the boiler and cooling  it sufficiently to allow the valves to be replaced.  Fortunately, the facility has sufficient backup boilers so that the resultant boiler downtime did not cause any lost time in the plant.

 Solving the problem was accomplished in two parts.  The first was a change in operating practices on the blowdown valve procedures.  The second part was a mall piping modification.  The plant’s blowdown procedure was to open valve A first, allowing cavity C to depressurize; then, open valve B.

 This blowdown sequence caused hot water to flow across the valve seat at high velocity into the unpressurized area as soon as valve B was opened, causing a slow erosion of the valve seat area.

 When the valves were then closed, valve B was closed first, allowing fluid to drain from cavity C.  Then, valve A was closed.  Between blowdowns, oxygen, which had entered cavity C as it was drained, attacked the seats and stem surfaces on both valves A and B.  This oxygen attack produced pitting and galling of the valve seat and stem area.  When the valve was operated, more damage occurred to the valve parts as the galled metal was ground between the sealing surfaces.

 By correcting the sequence of valve operation, cavity C is always full and pressurized, eliminating the influx of air.  Additionally, when valve B is opened against the dead-flow area in cavity C, no flow across seat B occurs and therefore, there is no erosion of the valve seat.

 Valve A, normally a slow opening valve, can be repaired or replaced at any time without shutting down the boiler, as long as the integrity of valve B is maintained.  However, replacing valve B requires the boiler to be taken off line and cooled.

 By instituting these simple operating procedures for bottom blowdown, unnecessary boiler downtime can be avoided, and equipment repair costs and overall boiler efficiency can be improved.

 Mark Botsford, CWT

District Manager



Preparing Cooling Towers and Heating Boilers For Winter Operation: Part 2


Have a competent service representative disassemble the low-water cutoff and makeup water feeding devices.  All parts should be thoroughly cleaned and reconditioned as required, then tested before the boiler is put into regular service.

  1. Burner equipment should be cleaned and adjusted to give maximum efficiency.  This can save fuel dollars.
  2. The safety/relief valve should be tested for freedom of operation.  This is of primary importance.  The boiler must not be fired if the safety/relief valve is inoperative or otherwise defective.
  3. All pressure and temperature controls and gauges should be checked for satisfactory operation and adjusted or replaced as necessary.  The water-level gauge must be cleaned to indicate the proper water level at all times.
  4. Any leaking pipes or fittings located on the boiler or anywhere throughout the heating system should be repaired or replaced to prevent a loss of water.
  5. Water lines exposed to freezing temperatures should be insulated to prevent freeze-up.  Steam and condensate return lines should be insulated to prevent unnecessary loss of heat.  Such action will reduce fuel bills and eventually more than pay for itself.
  6. All mechanical equipment, such as fans and pumps, should be checked for smooth operation and proper lubrication.
  7. A suitable record of boiler operation should be established and maintained throughout the season.
  8. The boiler heating surfaces should be cleaned of all deposits.  Dirty internal surfaces not only waste fuel and dollars but also can lead to the burning, bulging, cracking and eventual explosion of the boiler.
  9. If the boiler is of a type designed to permit cleaning of the water surfaces, this should be done and, where necessary, a suitable chemical treatment should be used to minimize new buildup of scale and to prevent corrosion.

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 By Mark Botsford, CWT


Scary Chart Time: Oil Price Trends

By Luke Wonnell

For those of you who are considering an oil-to-gas conversion for your building’s boiler system, let’s take a look at the commodity price for a barrel of crude oil over the past 12 months – that’s right, it’s scary chart time!


The current $70+/barrel is 67% higher than mid 2017 when the commodity price was closer to $43/barrel.  Now, let’s see the trends over the past 3 years:


Although crude oil is still relatively cheap compared to the 2013-2014 prices which exceeded $100/barrel, the recent trends are definitely going in the wrong directions for the upcoming heating season.  Now, possibly for the first time ever, we’re going to show you the month-by-month equivalent price of a “barrel” of No. 2 heating oil (42 Gallons)… that’s just the type of service we like to provide for you here at The Metro Group.


Since No. 2 and No. 4 heating oils are products of the crude oil refining process, the equivalent price per barrel is considerably higher than a barrel of crude oil (nearly double!).  Most buildings will benefit from keeping their fuel oil tank in place for backup or “interruptible” use, but it may be time to consider converting your boiler system to use Natural Gas as the primary fuel source in advance of the 2018-2019 heating season.

Call your Account Manager today to schedule a site assessment and see if you’re a good candidate for a gas conversion!


On Site Work: Replacing Manhole and Assembly

A manhole is an access hole typically located on the top side of the boiler.

It allows access for cleanings, washing out of debris and sediment, or repairs. The manhole should be opened annually, at a minimum, for internal inspection of the vessel.

When the cover to the manhole becomes corroded, it becomes both a safety and efficiency concern. If the manhole cover seals shut, the vessel cannot be properly inspected. If the cover seals incorrectly, with a space between the gasket and boiler, a steam leak can occur. This can happen on a steam boiler running for the purpose of creating heat. This will impact the boiler efficiency as you are losing steam while running the boiler for heat and also affect your fuel costs. While losing steam will cause you to burn more fuel, it is also an imminent safety concern as an individual who comes in contact with steam under pressure can be seriously injured. Any repair performed on a pressure vessel should be done by a professional, experienced, R-stamp certified mechanic.

ConEd Multifamily Gas Conversion Incentive Program – Must Apply Before May 18th!

By Luke Wonnell

ConEdison has structured a generous incentive program for multifamily buildings still on No. 4 heating oil, but you MUST submit your application BEFORE May 18th in order to qualify!  Click the link below for more information on this program:

This program is structured for multifamily buildings with 5-100 units and prioritizes customers who are still burning No. 4 heating oil.  ConEd is offering a $500 per unit incentive (up to maximum $50,000) AND additional equipment incentives (up to maximum $25,000).  These incentives will help pay for a portion of the project and expedite your ROI on the gas conversion project.

In order to qualify for this program you need to act quickly.  Call your Account Manager today to schedule a site assessment and see if you’re a good candidate for this program!



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On Site Work

Highland Terrace – Westchester Co.

Below we have a new boiler installed with a dual fuel gas/oil burner.  This is a hydronic system.  We installed a Heat-Timer HWR control panel with a 3-way valve to provide precise heating water temp. control to the building.  The heating water temps can be fine tuned to react to outside temps providing very comfortable apt temperatures while significantly reducing fuel consumption.

Lindy Coils & Hot Water Systems: Part 2

When you’re in the heart of the heating season (October 1st through May 31st) and your boiler’s running anyway to heat the building, it’s an absolute no-brainer to use the Lindy coil and make all your hot water.  This is arguably the most practical and cost-effective way to produce all the hot water for your building during the heating season.

However, when you’re outside the heating season, the economics of running your boiler to make hot water through the Lindy coil become much less attractive and it may be worthwhile considering an alternate hot water heater solution.  For example, say you’re in the middle of summer with 150HP steam boiler (6,000,000 Btu/hr) firing up to provide a peak 40GPM hot water load (roughly 2,000,000 Btu/hr) in the mornings and evenings when everyone’s taking their showers or baths.  Because you’re outside the heating season, the boiler’s controls are essentially bypassed to an aquastat which measures the boiler water temperature.  This aquastat will turn the burner on and off several dozen times each day in order to maintain the boiler water above a certain temperature needed to provide instantaneous hot water.  So the burner kicks on to heat up several hundred gallons of boiler water, simply to heat a few dozen gallons of domestic hot water… not terribly efficient.

Imagine an alternate system setup where you install 1 or 2 high efficiency hot water heaters burning Natural Gas to produce your domestic hot water in the summer months.  Now that behemoth boiler can take a rest for a few months while the 90%+ efficient hot water heaters chug along and produce exactly the right amount of hot water for your building and turn off when hot water is no longer needed.

This configuration provides some much-needed breathing room for a PLANNED shutdown of your boiler.  Now you have the luxury of scheduling a few days in the summer to take your boiler offline for a much needed fireside cleaning, waterside cleaning, burner overhaul, etc. without ANY interruption to domestic hot water!

This setup will also provide critical redundancy of domestic hot water production.  If for some reason your boiler goes offline in the middle of January, you can now use the gas-fired water heaters to provide hot water to your residents instead of being completely out of both heat and hot water.

The Metro Group, Inc. is proud to offer full life-cycle support for all your boiler room needs.  Call your Account Manager today if you need to schedule a fireside or waterside cleaning, arrange for a burner overhaul, install a replacement Lindy coil, or if you’d like provide 100% domestic hot water uptime to your residents.


Lindy Coils & Hot Water Systems Part 1

By Luke Wonnell

If you own a Scotch Marine or cast iron sectional boiler in the NYC metro area, there’s an excellent chance you have one or more Lindy coils installed in the boiler, which provide all the domestic hot water for your entire building on an instantaneous basis.  Depending on the size of your boiler, there are Lindy coils available that can produce up to 10,000 gallons per hour of domestic hot water – that’s 167 gallons per minute – amazing!

Very simply, Lindy coils are bolt-on removable heat exchangers which allow the potable domestic water to pickup heat from the non-potable water/steam inside the boiler.  NYC boiler codes require the use of a mixing valve downstream of the Lindy coil, because the exiting water is well above scalding temperatures.  For Scotch Marine type boilers, the Lindy coil will typically be installed on the top of the front tubesheet (left photo below) while for cast iron sectional boilers, the Lindy coils are installed in one or more of the intermediate sections (right photo below).

There are many different configurations of Lindy coils available – the image below shows just a few of the available configurations:


Boiler Re-tubing: On Site Work

Below are pictures of a recent boiler tube replacement in Brooklyn. During this project we Torched and cut 25 old, corroded bottom boiler tubes (picture 1). Once cut, these tubes are removed from the boiler and the boiler room itself. The boiler vessel and tube drum are then flushed clean. Twenty five new U.S steel boiler tubes are then installed and rolled tight for a proper seal with the front and back tube sheets (picture 2). The boiler is filled with water, recharged with our inhibitor for proper chemical protection (a necessity with new steel and fresh make up water now inside the boiler), and the boiler doors are re-gasketed and checked for leaks. In addition to the replacing the boiler tubes, we also installed a new Dry Oven and interior insulating refractory wall (picture 3 and 4).


Heat Flux and Boiling Regimes: Part 3

In an ideal world, all the waterside metal surfaces inside your steam boiler would be exactly 86°F / 30°C above the boiling point when the burner is firing. This would result in perfect boiling everywhere throughout your boiler, maximizing the operating efficiency.  While this isn’t fully achievable in the real world, the manufacturer typically designs the boiler for Region I / II operation by providing at least 5 ft2 of heat transfer surface area per Boiler Horsepower. This ensures sufficient heat transfer surface area inside the boiler to avoid Region III / IV boiling.

By performing routine preventative maintenance (annual fireside cleaning, periodic waterside cleaning, and annual burner overhaul/tune-up) you will keep your steam boiler operating in tip-top shape and avoid Region III / IV boiling. Call your Account Manager at the Metro Group today to learn more about our preventative maintenance services!