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Fully condensing boilers can fire as high as 99% efficiency and attain a higher efficiency in different ways. If you stop to think about it, these boilers are simply deleting as much energy from the gasses as physically possible, prior to exiting the building in the form of flu gasses. The key challenge created by this process is the handling of condensation. Condensation is a very acidic liquid formed anytime our outlet temperature drops below 120F or gains over 85% efficiency. This is a simple rule of thumb. Once those parameters have been met, we have to deal with the condensation so it does not destroy the boiler or vent system. So here starts the ‘condensing game’. Be careful and consider the following prior to choosing a condensing boiler system:
VENTING:
With the above criteria met, the product should be rated as an ANSI category II (negative/corrosive) or IV (positive/corrosive) appliance. This means a special alloy stainless steel vent system called AL29-4C is required by code. This vent system can be manufactured by Schebler, Heat Fab, Zflex, or a small number of other manufacturers (UL listed products should be important to you). This material is to prevent damage and/or possible leaking from the vent system. You CANNOT vent a true high efficiency boiler through a masonry chimney as the mortar will fall apart and the chimney will fall in. This means you have to line your chimney with the AL29 which may be expensive and subtract from the payback based on first cost.
Many of the high efficiency boilers can vent through a side wall directly but you have to pay close attention to the maximum length and the equivalent run and the elbows or fittings. In addition, you must watch how you will exit the building as condensation can stain the side wall and the certain plume thrown from a high efficiency boiler may impede a view or an employee’s concentration from windows above the vent outlet.
Last but not least, you have to be very careful of the ‘wannabe’ boilers. These are the boilers that sit at 87 and 88%. They ‘wannabe’ NON CONDENSING when the contractor figures out the vent material for condensing cost a whole lot more, and they ‘wannabe’ high efficiency when the customer wants a condensing boiler. The ‘wannabes’ typically cost much less than the full condensing guys, but warrant some attention here in this section. Improper venting can be the demise of a very expensive boiler.
Engineer’s Beware: Considered equal products can require different vent materials. This can be a nightmare waiting to happen. I’ve seen chimney’s cave in because of this. Be careful to disclaim, in your specs and schedules, so you are covered in the world of confusing venting codes. If you are in question at all, give us a call and we can review your vent routing and your equal products to be sure you have nothing to worry about. A classic mistake would go something like this:
Basis of design is the RBI Futera II series boiler model FB1950. Equal products may be provided by:
Lochinvar
Thermal Solutions
Patterson Kelly
Now, go back to your Sesame Street days and figure out which of those DON’T belong. All of the manufacturers here are considered quality providers and name brands (this is important because today, too many copy cat copper fin boiler manufacturers with less than 5 years experience are out presenting as equals).
The dilemma is Lochinvar’s equal is the PFN boiler and the PFN boiler has been rated as a category II or IV appliance (unless this has changed). This requires AL29 vent material. If you are venting into a chimney, the Lochinvar would need to use a liner while the Patterson Kelly and RBI carry an ANSI Category-I rating and can vent directly into the chimney and meet NFPA54 codes. The problem can get worse because now a wholesaler may say.. ‘hey, they are bidding the category-I so I can use the Copper Fin II’. Now the scope of your job is changing because the footprint, piping, control, wiring and who knows what else will change on the sprawled out Copper Fin II vs the Down fired Powerfin unit that meets the arrangement of the RBI Futera or the Patterson Kelly Thermific.
At the end of the day, the Thermal Solutions product will also carry a category II or IV rating so they’ll need a liner as well (maybe).
STAY OUT OF TROUBLE BY:
Ο Disclaiming the vent material by demanding it meet NFPA54 and ANSI category standards at the expense of the installing contractor when the basis of design is not being used.
Ο Using a rule of thumb that says anything over 85% combustion efficiency can condense and will probably need an AL29 vent material (Thermal Solutions is 88% and Lochinvar Powerfin is 87%).This being the case, they may not be your best equals for this project, or you might bring the basis of design in line with these products (RBI would be a Futera III and Paterson Kelly would be a Modufire) so they are all true equals. Your basis of design rep should help you with this.
Ο Always NAMING the manufacturers model number or series. This will prevent the ‘you named them you have to take them game’ that some reps or suppliers can play. It’s much easier if our example project would have said: RBI Futera III is the basis of design with equal products being the Lochinvar Powerfin only, Thermal Solutions Evolution only, and the Patterson Kelly Modufire only. No confusion left for the contractor and no ‘creative angle’ for the bidders.
Ο Last but most important calling and letting us review your venting. We truly are the most knowledgeable representative firm when it comes to venting and up to date codes. We have to be because a big part of our business is providing guaranteed venting solutions for everything from clothes dryers and fireplaces, to grease duct and boilers.
(Go directly to our line of HIGH EFFICIENCY boilers and water heaters)
RETURN TEMPERATURE:
Most or all commercial condensing boilers rely on a very low return temperature to achieve a very high efficiency. For instance, if your system is running at an average temperature of 160F-180F you probably will not be served well by ANY condensing boiler. At these temperatures the boilers are unable to condense and fire more in the range of 85-88%. You should always review the efficiency charts as each legitimate manufacturer publishes one. This said, the condensing boilers typically cost 30-40% more than medium efficiency boilers. Combine this with expensive vent material and possible control challenges and you'll find that the payback is just not there.
If you are working in a system with reheat or seasonal ability to run at lower temperatures, there may be a payback. In this case, you simply have to pay close attention to your maximum and minimum temperatures to carefully plan your flow rate through the boiler (see flow and piping). You should look to see what the minimum acceptable temperature is as applications such as Snow Melt or Heat Loop can be perfect for this. (Go directly to our line of HIGH EFFICIENCY boilers and water heaters)
FLOW AND CONTROL:
Don't get caught up in the 'turndown' game. Most of the time literature will concentrate on maximum performance that happens a minimum of the time. Kind of like the car add that says "LEASE FOR $129 PER MONTH"... fine print says "$22,000 down, does not include tax or security deposit". A reasonable turndown is anywhere from 4:1 to 10:1. Because the boilers almost always operate at a higher efficiency in low fire, multiple boilers firing on low before modulating up are best. In the same token, some advertise a high turndown that is of little value. If you are specifying or installing two (2) 1000MBH boiler that you intend to fire each in low fire, prior to high fire, and the turndown is 5:1 you will get an output of around 180MBH. Times 2, you can provide the building with 360MBH at maximum efficiency. If boiler manufacturer "X" advertises the same size at a 20:1 turndown to maximum efficiency, the unit can only provide 45MBH each unit. Together it is only 90MBH. This said, pilots have more BTU's than this and the boiler will more than likely not be running at all, so the turn down becomes rather in significant. Still, modulating the boiler to meet the load demand is incredibly important so the ability to do this with existing building management or a stand alone control on the boiler is important. You CANNOT simply set one of these boilers and not control them.
Flow can be critical for a couple reasons. In the case of a copper fin boiler, flow is optimized to achieve about 7' per second. This rate will protect the exchanger from eroding (flow too fast) or liming, blocking, and melting (flow too slow). In other types of condensing boilers the flow may not be critical to the longevity of the vessel, but will be critical to the operating temperatures. If the boiler provides a 30F delta T at about 200gpm, slowing down the flow will increase the Delta T (difference between incoming water and outgoing water). Faster will lower it. If you are running a system at 180F in the dead of winter, you'd better look closely at the flow and Delta T. If you only have 75gpm available and the Delta T rises to 80F you are in trouble because no system can handle an outlet supply water temperature of 260F. You will trip the high limit. (Go directly to our line of HIGH EFFICIENCY boilers and water heaters)
WARRANTY AND MANUFACTURER:
Warranty is always important but absolutely critical when a product is highly proprietary. For instance, brand "X" may make a wonderful condensing boiler, but if the temperature control system, the flame monitoring system, and the gas train components are proprietary, where will you get them and how much will they cost? Of course you'll want a very long warranty. With the era of 'copy cat' manufacturers, you have to look for experience and a well known manufacturer. This is not the time to make a new guy an equal!
Typical warranty should be 10 years of the vessel and at least a year on the parts. I have a little industry secret... boilers DON'T thermal shock which is why everyone and their brother now advertise thermal shock warranties over 20 years. If they don't, you should probably ask if you should worry about that. In the industry it's common to require a local service company, representative, or factory trained tech commission the equipment. Don't pass on this as is it CRITICAL to good operation and optimum efficiency. In addition to the manufacturers warranty DEFINITELY require that the unit be shipped with TWO (2) fully years of warranty parts AND labor. Do not accept exceptions in this matter as the equipment is highly proprietary. (Go directly to our line of HIGH EFFICIENCY boilers and water heaters)
MAINTENANCE AND SERVICEABILITY:
Ask how the tubes or vessel are repaired. Ask how adjustments are made. Ask where parts are available. Watch the height of these units because many will require a top service clearance for burner service, adjustment, and tube replacement. Be sure to look closely at the firing system and flame monitoring systems. A flame 'eye' is better because it's easy to change, last longer, and is very reliable. A flame 'rod' requires replacement and adjustment more often. If this is the case, be careful again, about the service clearances. Find out if fault codes read out like the common RM7800 Series Honeywell FSG does, or if you will need a PC to decode a fault. This can merry you to the manufacturer for life and at a premium. Be sure corners aren't cut in this regard either. For instance, the use of the Honeywell S86 residential flame control is simply cutting a very important corner. (Go directly to our line of HIGH EFFICIENCY boilers and water heaters)
RELATED ENERGY SAVINGS COMPONENTS:
Exhausto: When using multiple boilers, you should be sure to do a full venting and combustion air calculation. Exhausto can save the end user dollars by taking multiple stacks and shrinking them to an affordable AL29 common vent system. They also provide a wonderful source of combustion air instead of a large open louver. Last they can limit excessive draft on high chimneys which cause poor combustion and random lock outs! (Go directly to our line of HIGH EFFICIENCY boilers and water heaters)
Mestek: Developed a wonderful control platform for the KN Series boilers. This system communicates with the other boilers as well as the building management system. It's a first of it's kind and will assist the end user in achieving and optimum efficiency from the boiler system. (Go directly to our line of HIGH EFFICIENCY boilers and water heaters)
UP TO 98% EFFICIENCY IN A COMPLETELY PACKAGED DURABLE CAST IRON DESIGN
Mestek does it again! With a combined effort of Smith and Hydrotherm, Mestek manufactures an industry leading fully condensing cast iron boiler. The boiler is fully packaged with the technical benefits of today's high efficiency boilers in a durable long lasting, non proprietary 30 year cast iron design!
Sizes: 600, 1000, and 2000 MBH inputs * Flame Safeguard Design: Honeywell RM7800 Series
Flame monitoring system: UV Honeywell scanner (external) * Maximum Efficiency: 98%
Max. Turn Down: 5:1 * Minimum Return Temperature: None (liquid) * Minimum Gas Pressure: 2" WC
Diagnostics: Honeywell S7800 screen included * Max./ Min. Flow: 30 - 300 gpm (KN20)
Warranty: 10 years on cast iron sections, 1 year on parts, 21 years against thermal shock
Options: HeatNet energy management system, various codes, extended labor warranty, factory start up
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HIGH EFFICIENCY COPPER FIN SYSTEMS FOR POOLS AND DOMESTIC WATER APPLICATIONS:
The gas-fired Futera Fusion™ now brings the field-proven performance of Futera III Modulation boilers and water heaters to the ultimate levels of efficiency and reliability. This innovative design is the ideal choice for applications with low operating, return, or make-up water temperatures. Unlike most condensing products available today which publish the highest efficiencies at the lowest inputs, the Fusion is capable of attaining efficiencies as high as 98% at Full Input! The full modulation firing system continuously varies the energy input to precisely match heating load without over-firing and wasting fuel. This provides extremely high part-load efficiencies.
The condensing secondary heat exchanger is solid stainless steel and designed to operate at the boiler's full flow rate. It operates in full condensing mode at all times, while a state of the art temperature mixing system protects the boiler's primary heat exchanger. There's simply no better way to protect an owner's investment. This design also offers a larger heat transfer surface area than any competitive product currently available.
Sizes: 500 to 2000 MBH inputs * Flame Safeguard Design: Honeywell RM7800 Series
Flame monitoring system: UV Honeywell scanner (external) * Maximum Efficiency: 98% at FULL INPUT
Max. Turn Down: 3:1 * Minimum Return Temperature: None (liquid) * Minimum Gas Pressure: 2" WC
Diagnostics: Honeywell S7800 screen included * Max./ Min. Flow: See Literature for various sizes
Warranty: 10 years on the heat exchanger (5 years as a water heater), 1 year on parts
Optional: Extended labor warranty (up to 5 years), factory start up
LEARN MORE ABOUT THE UNIQUE FUSION BOILERS AND WATER HEATERS