FAQ | Boilers and Heat Source Equipment

Boilers and Heat Source Equipment Questions

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What is the most common heat source for a radiant heating system?
What size boiler do I need for my radiant heating system?
Should I replace my existing boiler with a more efficient unit?
Are tankless waterheaters a good boiler substitute for an Eichler radiant panel heating system?
Boiler and tankless waterheater condensation problems and efficiency ratings. Explain?
I don't want a boiler. What are my options?

What is the most common heat source for a radiant heating system?

The most common heat source is a hydronic boiler. Different from a domestic water heater, it has relays, transformers, aqua-stats, gas ignition systems, safety controls and is designed to accommodate increased output and flow rates often required by radiant panel systems. A typical residential water heater holds 40 gallons of water and has an output rating of approximately 40,000 BTU. A typical residential copper or stainless steel boiler will hold 1-3 gallons of water and output 100,000-225,000 BTU. Cast iron boilers usually hold more water, between 5-20 gallons total. Typically less storage means less standby loss and high output means faster temperature generation. Hydronic boilers are designed for the application where most water heaters are not. Some water heaters can be used for small radiant heating applications. Back to Top

What size boiler do I need for my radiant heating system?

The size of the boiler depends on the output required to offset the heat loss of the structure according to specific climates and weather conditions. Simple heat loss calculations will provide an ideal input size. It is important not to undersize or oversize a boiler. Under-sizing a boiler will lead to unsatisfactory heating and cause the unit to run continuously. Although a boiler “under load” is more efficient than one turning on and off, if it can’t raise the supply water output temperature to the preferred optimum design range then the house will not heat in a timely manner. Over-sizing a boiler will lead to boiler short cycling, additional wear and tear on support equipment, and reduce efficiency. When we size a boiler, we look at the requirements for the system input and depending on the mass of the concrete slab to be heated, we upgrade the output 20-30% over what’s required. This allows the boiler the thermal pick-up during system start-up plus assures system performance during cold spells and minor boiler efficiency loss over the years. Nowadays for multi-zoned systems, we employ multi-staged gas valves, thermostatic modulation valves , or outdoor reset controls which vary the boilers output capacity according to current demands. Also, storage tank systems which store water at a desired set temperature act as a “buffer” between larger boilers and smaller zoned systems. The radiant panel demands will pull water directly from the storage tank instead of from the boiler. It is important to have a high efficiency insulated tank for water storage so standby loss is minimized. Back to Top

Should I replace my existing boiler with a more efficient unit?

The question should be answered after performing a thorough evaluation of your existing boilers condition. Sometimes a simple cleaning can restore lost performance of a boiler system without having to replace it. Chances are if the boiler is 25-50 years old, its replacement could be a practical move. Modern technology and boiler design have advanced boilers in safety and efficiency. For a standard boiler replacement, our customers have experienced a 35-45% savings off their monthly heating bill, with some cases being as high as 50% or more. Many older boilers still in service were fairly efficient in their best day, but have reduced operational efficiency from the years of service. Many different options exist today for their replacement. California Code requires a minimum 80% efficiency rating on all boilers produced. Due to minor efficiency variances, many boilers are engineered for 82-85% efficiency to meet the legal standards. Then there are ultra high efficiency boilers which are producing 92-96% efficiency which are the common choice nowadays in our area since the California Air Resources Board requires certified low nox heating units to be installed which these boilers meet. They use sealed combustion chambers and secondary stainless steel heat exchangers for “condensing”. Condensing boilers use steam vapor produced by the systems cool return water temperatures entering a hot heat exchanger to trap additional energy. The additional energy in the steam exchanges back into the system water and efficiency is increased. Back to Top

Are tankless waterheaters a good boiler substitute for an Eichler radiant panel heating system?

As a service to our customers, we feel there is a professional responsibility to inform and educate the public on the proper use of tankless water heaters like the Takagi TK-1 and TK-2 and why they are a poor choice to substitute for an originally specified boiler in the Eichler radiant panel system. When installed as the heating source for the Eichler, these units are less efficient; they may not provide adequate BTU at the required flow rates to properly heat the home under design conditions; they contain improperly designed modulation (firing) controls for the application; they are not ASME (American Society of Mechanical Engineers) approved for space heating; they are restricted from installation and permitting by Bay Area cities as boiler substitutes without an engineer’s study, approval, evaluation, and supporting documentation; they do not meet the original specifications as outlined for the Eichler home heating system. We cannot imagine a single instance from a design and engineering standpoint where a tankless water heater can be shown to be more efficient, i.e., will use less fuel, than a low-mass or high efficiency condensing boiler when used in the same Eichler home. Since the cost to install either a tankless water heater or a boiler is relatively the same and may in some instances be less for the comparable boiler, why would anyone choose to install a tankless water heater as a substitute for their boiler? As a consumer, this purchase doesn’t make any sense if you understand all the parameters involved with the system function and design. For domestic hot water generation in an "open-loop" system, tankless water heaters perform as designed, but with limitations. The manual is specific in indicating these units have a maximum flow rate of 6.9 gallons per minute (gpm). At a flow rate of 6.7 gallons per minute with an incoming water temperature of 70 degrees F, the output temperature at the faucets will be 110 degrees F assuming no piping losses. If the incoming water temperature is cooler, i.e., 50 degrees F, the output temperature will still be 110 degrees but at a reduced flow rate of 5.2 gpm. This is why you can not operate a dishwasher, washing machine, or one, two, or even three showers simultaneously. As a consumer, the method you would use to obtain hotter water at multiple faucets would be to simply reduce the amount of water being used at each faucet. The manufacturer does not list in the TK-2 manual or their sales brochure any performance factors for flow rates greater than 6.7 gpm or a supply water temperature greater than 70 degrees F. Why? The answer is simple. It is the relationship between the flow rate and output temperature which determines the appliance limitations and efficiency. With return water temperatures of 105-110 degrees F or greater as in a radiant panel system, supplying a Takagi TK-2 water heater with these elevated temperatures will result in the mechanical modulation system reducing the burn rate causing efficiencies to drop to 40% or more. More fuel is used to obtain a required room temperature because the low-burn condition causes the unit to operate longer. All boiler engineers will agree that any boiler or like appliance is most efficient when firing under full load and not being mechanically modulated. Condensing boilers like the Munchkin designed to "fully-modulate" by providing a variable mixture of both gas and air can achieve extremely high combustion rates (97%) and efficiencies (92%) unlike the Takagi TK-2. The efficiency rating as stated by manufacturers is often deceiving and depends on the product application. The Department of Energy (DOE) defines the testing methods used for boiler and water heater products, while the testing agency, GAMA (Gas Appliance Manufacturers Association), performs the tests to certify the ratings. On 9/26/02, we requested GAMA clarify their testing methods and procedures for boilers and tankless water heaters. The engineering staff representing GAMA has stated, "The AFUE and EF ratings are not comparable. As suggested, they are based on two specific test methods which result in different conclusions. AFUE is specific to space heating products and takes into account the typical seasonal space heating requirements. EF is specific to residential water heaters and takes into account the typical daily water usage of the average residence. The DOE does not require tankless water heaters to be tested as space heaters, so our certification program has not tested tankless water heaters using AFUE methods." In conclusion, when one is told a tankless water heater has an EF rating of 85%, this efficiency factor is erroneous and not applicable to space heating. When one is told a boiler has an AFUE (annual fuel efficiency utilization) of 92%, this indicates a measure of the amount of fuel converted to space heating in proportion to the amount of fuel entering the boiler. For the Eichler radiant panel system, EF has no meaning what so ever while AFUE is the only efficiency rating that has meaning and which should be considered. Because of the conditions created by the Eichler system design, a tankless water heater will use more fuel and be less efficient than a comparable boiler. As indicated, it must operate longer and burn more fuel to obtain the needed heat for the conditioned space. The facts of the Eichler radiant panel design and original specifications for the tract and custom home are as follows: 1) The copper and steel tubing systems of the radiant panel were composed of 1/4", 3/8", 1/2", 3/4", 1", and 1-1/4" nominal sizes; 2) The common boilers used were Thermakit, Racon, A.O. Smith, Raypack, and Mueller ranging from 80,000 to 199,000 BTU. These were all low-mass copper and steel tube boiler designs with some containing cast-iron heat exchangers; 3) In the earlier models, the boilers were generally sized 30%-50% greater than the actual heat loss of the home for increased pick-up and reduced lag periods. The BTU outputs were reduced and over-sized to 10%-20% in the later models; 4) The BTU heat loss of an originally constructed Eichler home was determined to be 45-55 BTU per sq.ft.; 5) The original pumps for the radiant panel circuits were all high head high flow (gpm) units like the B&G HV, B&G PR, TACO 111, Dyna Pumps, and Rheomatics. These model pumps averaged a flow rate of 15 gpm @ 20 ft. head; 6) The tubing spacing was between 12"-18" on center. The serpentine tubing layout was in both parallel and series arrangements; 7) The original specifications called for a flow rate of 1-2 gpm per room circuit which can be supported by the pump choices. The tubing sizes were chosen accordingly to accommodate 10,000 BTU output @ 1 gpm and 18,000 BTU output @ 2 gpm. Check the return manifolds located in a central closet or the mechanical room. If you multiply the total number of tubes by 1-2, it is a satisfactory indication of the gpm needed to heat the home. When doing this, remember some homes with less tubes may require greater flow rates than indicated previously. Also, it never hurts to increase the flow rate over the design parameters up to the limitations of the tube size and boiler output since this can result in faster and more efficient heating of the home; 8) To obtain the desired room temperatures of 70 degrees F and offset the heat losses of the home, the supply water temperatures produced by the boiler needed to be 130-140 degrees F. This would be obtained by a boiler capable of providing these water temperatures at an average flow rate of 15 gpm with a 20 degree temperature rise (delta T) between the return and supply water temperatures. The amount of tubing surface is an important factor in providing enough heat transfer (BTU) to the living or conditioned space. The original designers because of inexperience didn’t know the exact BTU transfer capability of the tubing sizes nor the total amount of linear tubing necessary to heat the home. It is a fact the original designs contained a lot of guess work for this application. We must congratulate the original engineers for their excellent work. Once they gained more experience, however, they found the tubing size and amount of tubing could be reduced while still meeting the original design specifications. This is why many of the later models have 1/4" and 3/8" circuits. The limitations of the smaller tubing were obvious. The flow rates and pumping heads needed to be increased so high head and high flow rate pumps were specified to compensate for not only the smaller size of the tubing but the lesser amount which was installed. We contend for all the previous reasons there are limitations on which appliances are better designed to provide heat for the Eichler home. Boilers that have the proper flow rates, 10-20 gpm, and the BTU output capabilities closely matching the original design requirements are a better choice and work more efficiently. Installing an improper pump, i.e., one with less flow rate and head, always results in slow inefficient heating and poor boiler performance. The same is true if you install a boiler with too little BTU output for the application. We have heard there have been claims some homeowners are completely satisfied with the performance of the TK-2 tankless water heater. We also know many of these systems have not been permitted or inspected by the authority having the jurisdiction resulting in state and local safety code and construction violations which have failed to be identified. In our area, all water heater and boiler installations are required to be permitted and inspected by local officials. We submit with all the variables considered, customer satisfaction is only a subjective measurement often clouded by misinformation and misunderstanding and if these homeowners had chose any boiler rather than a tankless water heater, the facts are irrefutable their energy bills would be less and overall system efficiency would be greater. Manufacturer warranties are important. All appliances by law must have a manufacturer warranty covering the appliance for a minimum of (1) one year. Contractors and other installers often provide additional warranties to supplement those of the manufacturer. Most manufacturers provide "limited warranties" for their products which give the consumer specific legal rights that may vary from state to state or according to other conditions. Any warranty is only as good as the company who provides the product and often limited to the original retail buyer while containing many exclusions and disqualifications. The following are some examples of various manufacturer warranties: 1) Teledyne Laars Residential gas-fired hydronic boilers – 20 years limited; Munchkin – 12 year limited; Takagi TK-2 when used in space heating applications – 1 year limited. Since Anderson Radiant Heating has always provided top quality installations, products, and services, we are proud to offer at no additional charge a (3) three year parts and labor warranty and inspection service in addition to any manufacturer’s warranty. This applies to the original purchaser or any subsequent buyer. There are many excellent boilers on the market which will perform well in the Eichler home. Tankless water heaters are not boilers. Because of their design (used primarily in "open-loop" domestic water generation), mechanical modulation, and low flow rate and temperature output, this appliance is not the best choice nor should it be used as a boiler substitute in the Eichler home which contains a "closed-loop" system. We recommend either the Teledyne Laars JVS/JVH or Munchkin models. A Munchkin 140 with a 92% AFUE (annual flue utilization efficiency) and a delta T of 20 degrees F @ 14 gpm is an excellent choice to heat the average Eichler home. Back to Top

Boiler and tankless waterheater condensation problems and efficiency ratings. Explain?

There should be little concern for condensation damage to modern boilers when the unit is properly sized (sufficient BTU output for the home) and installed in accordance with the manufacturer’s recommendations. The fact is for every therm (100,000 BTU) of gas burned, 1.15 gallons of water (condensate) is produced by any gas appliance because of the combustion process. The major concern should be how the appliance removes the condensate. Boilers are designed to either evaporate the condensate, drain it to an external source, or do both. A tankless water heater is not a boiler. It simply evaporates any condensate by having a very high BTU burn-rate at a low flow rate. Under the right conditions however, it will condensate like any low-mass boiler. So both units produce condensate because of combustion. The other concern is heat exchanger failure caused when condensate is abundantly produced because of system design parameters. When cold return water as is prevalent in a radiant panel system comes in contact with a hot appliance heat exchanger, the cooling process may produce additional water (condensate) through "sweating". This water is slightly acidic and can result in corrosive damage to the heat exchanger when not removed. The manufacturer and design engineer will agree the solution to this simple problem is to insure the boiler sizing and piping designs compensate for this condition. A "condensing boiler" is designed to use the condensate to increase burning efficiency. The condensate actually plays an important role when it is captured in a secondary heat exchanger thereby extracting more BTU which can be transferred as heat into the home. This is why a condensing boiler, such as the Munchkin, can achieve a true AFUE (annual fuel utilization efficiency) of 92%. The boiler is made with stainless steel which can resist the effects of any corrosion caused by the process. A non-condensing boiler, such as a Teledyne Laars, is a low-mass boiler and can have problems with condensation when installed in the Eichler radiant panel system. We have however never seen any of these problems with our installations. Why? When the boiler is properly matched for the Eichler heating load (adequate BTU output and flow rate) and contains sufficiently sized by-pass piping as recommended by the manufacturer, there is no condensation problem. All condensation problems are caused by human installation factors. We have seen many installations where the by-pass piping was too small, incorrectly installed, plumbed as a mix rather than a by-pass, designed as primary-secondary circulation loop when inappropriate, or any number of other combinations. When condensation problems exist with of these types of boilers the installer just made a mistake or didn’t understand how to install the product for the application. It’s been said before, "When all else fails, follow the instructions". The installation manual gives specific procedures to follow in order to prevent these problems. Besides, modern boilers like the Teledyne Laars and Munchkin are built with materials to help prevent heat exchanger damage from condensation is most circumstances. The efficiency rating as stated by manufacturers is often deceiving and depends on the product application. The Department of Energy (DOE) defines the testing methods used for boiler and water heater products, while the testing agency, GAMA (Gas Appliance Manufacturers Association), performs the tests to certify the ratings. On 9/26/02, we requested GAMA clarify their testing methods and procedures for boilers and tankless water heaters. The technical staff representing GAMA replied as follows: "The AFUE and ER ratings are not comparable. As suggested, they are based on two specific test methods which result in different conclusions. AFUE is specific to space heating products and takes into account the typical seasonal space heating requirements. EF is specific to residential water heaters and takes into account typical daily water usage of the average residence. The DOE does not require tankless water heaters to be tested as space heaters, so our certification program has not tested tankless water heaters using AFUE methods". In conclusion, when one is told a tankless water heater has an EF rating of 85%, this efficiency factor is erroneous and not applicable to space heating. When one is told a boiler has an AFUE (annual fuel utilization efficiency) of 92% this indicates a measure of the amount of fuel converted to space heating in proportion to the amount of fuel entering the boiler. For the Eichler radiant panel system, EF has no meaning what so ever while AFUE is the only efficiency rating that has meaning and which should be considered. Back to Top

I don’t want a boiler. What are my options?

You might have no options at all. It depends on the size of the system and the input requirements. Small additions (less than a 1000 square feet) can be heated from a water heater with the proper equipment and set up. A water heater can take up more room than a boiler so if space is a concern then you can rule that out. A radiant panel system can be heated from a solar system if the area permits and the system is originally installed with just solar heating in mind. A proper solar system may require a large storage tank to collect and store the water for heating the radiant panel. If a solar system is used for heating the radiant panel, a supplemental system which relies on a back-up heat source such as a boiler must be provided. The total cost of the equipment to install an adequate solar space heating system would be three times the cost of a boiler or more. And there you have it. From a hydronic standpoint, no boiler, probably no radiant heating system. You can, however, install electric radiant heating mats. They draw a lot of electricity and therefore are expensive to run in many areas. Also they require serious upgrades to the electrical service of an average home. Usually radiant heating mats are used for small floor warming applications and not space heating. Initial costs can also be really high for those systems. Back to Top Back to main FAQ