- This topic has 7 replies, 4 voices, and was last updated 20 years, 11 months ago by Harold Kestenholz.
22 Dec 2000 at 5:15 am #274217Anonymous
I’m considering a tankless hot water system. Looking for opinions from anyone who has experenced owning one. Reliablity, efficiency, etc.
23 Dec 2000 at 7:57 am #289376SylvanLMPParticipant
Before you decide to go with a tankless coil set up You should have a Licensed plumber Or your local utility or gas supplier perform a Bacharach test for efficiency of your boiler.
If your using oil and getting a rating of 60% or gas with any efficiency less then 80% you maybe spending a lot more money then going with an indirect tank installed as a separate zone.
The new indirect tanks have very little stand by losses compared to firing a HUGE boiler year round just to make water hot.
There are several options available today that you can get hot water during the winter months that cost next to nothing using your existing heating system whether it be steam or hot water (heat pumps don’t work as well unfortunately)
You local licensed Master plumber or Heating contractor should be able to give you a projected cost for your investment after performing the above tests.
stack temperature ,smoke, CO etc
24 Dec 2000 at 12:31 am #289377Harold KestenholzParticipant
Since 1990, a tankless coil boiler has a minumum AFUE of 80%. Most are rated higher than the minimum. A water heater does not have that efficiency as it is a single-pass vertical heater. A tankless coil boiler with an input of 140,000 btuh, equal to a 1 gallon per hour nozzle, can deliver 3 gallons per minute (180 gallons of hot water per hour.) When mixed with cold water it can produce 5 gallons per minute of shower water every hour of the day or all month if your budget allows. There is nothing else besides an external tank system that can deliver this, although an external tank can only produce this much in the first draw for the tank and far less for the following hours.
If you buy another water heater instead of using the tankless coil system, you now have two heaters, one for the house and one for the hot water – with two burners to service. Now the boiler doesn’t have to stay warm for the summer months to make hot water, the extra water heater does – all year round. So which is better? – To have a tankless coil boiler weighing 360 pounds losing heat from the jacket during the summer (it is doing the heating during the other seasons), or a water heater weighing 350 pounds (including the water content) losing heat from the jacket all year round.
I opt for a high efficiency tankless coil boiler set up with a mixing valve so there is only one heating appliance to service with only heat losses from one appliance instead of two, making more hot water than most people can use.
24 Dec 2000 at 3:10 am #289378Frank HiebertParticipant
I hate to disagree with the two previous gentlemen however I believe what you are talking about is an instantaneous water heater. It has been very popular in Europe and Japan for many years. You probably don’t have a boiler if my hunch is right and are looking for an alternative for your hot water tank. If my hunch is correct the following bit of information may be useful to you. Then be sure to have a qualified plumber do the work for ya..
3rd yr apprentice
Water heating accounts for 20% or more of an average household’s annual energy expenditures. The yearly operating costs for conventional gas or electric storage tank water heaters average $200 or $450, respectively. Storage tank-type water heaters raise and maintain the water temperature to the temperature setting on the tank (usually between 120° -140° F (49° -60° C). Even if no hot water is drawn from the tank (and cold water enters the tank), the heater will operate periodically to maintain the water temperature. This is due to “standby losses”: the heat conducted and radiated from the walls of the tank—and in gas-fired water heaters—through the flue pipe. These standby losses represent 10% to 20% of a household’s annual water heating costs. One way to reduce this expenditure is to use a demand (also called “tankless” or “instantaneous”) water heater.
Demand water heaters are common in Japan and Europe. They began appearing in the United States about 25 years ago. Unlike “conventional” tank water heaters, tankless water heaters heat water only as it is used, or on demand. A tankless unit has a heating device that is activated by the flow of water when a hot water valve is opened. Once activated, the heater delivers a constant supply of hot water. The output of the heater, however, limits the rate of the heated water flow.
Gas and Electric Demand Water Heaters
Demand water heaters are available in propane (LP), natural gas, or electric models. They come in a variety of sizes for different applications, such as a whole-house water heater, a hot water source for a remote bathroom or hot tub, or as a boiler to provide hot water for a home heating system. They can also be used as a booster for dishwashers, washing machines, and a solar or wood-fired domestic hot water system.
You may install a demand water heater centrally or at the point of use, depending on the amount of hot water required. For example, you can use a small electric unit as a booster for a remote bathroom or laundry. These are usually installed in a closet or underneath a sink. The largest gas units, which may provide all the hot water needs of a household, are installed centrally. Gas-fired models have a higher hot water output than electric models. As with many tank water heaters, even the largest whole house tankless gas models cannot supply enough hot water for simultaneous, multiple uses of hot water (i.e., showers and laundry). Large users of hot water, such as the clothes washer and dishwasher, need to be operated separately. Alternatively, separate demand water heaters can be installed to meet individual hot water loads, or two or more water heaters can be connected in parallel for simultaneous demands for hot water. Some manufacturers of tankless heaters claim that their product can match the performance of any 40 gallon (151 liter) tank heater.
Selecting a Demand Water Heater
Select a demand water heater based on the maximum amount of hot water to meet your peak demand. Use the following assumptions on water flow for various appliances to find the size of unit that is right for your purposes:
Faucets: 0.75 gallons (2.84 liters) to 2.5 gallons (9.46 liters) per minute.
Low-flow showerheads: 1.2 gallons (4.54 liters) to 2 gallons (7.57 liters) per minute.
Older standard shower heads: 2.5 gallons (9.46 liters) to 3.5 gallons (13.25 liters) per minute.
Clothes washers and dishwashers: 1 gallon (3.79 liters) to 2 gallons (7.57 liters) per minute.
Unless you know otherwise, assume that the incoming potable water temperature is 50° F (10° C). You will want your water heated to 120° F (49° C) for most uses, or 140° F (60° C) for dishwashers without internal heaters. To determine how much of a temperature rise you need, subtract the incoming water temperature from the desired output temperature. In this example, the needed rise is 70° F (21° C).
List the number of hot water devices you expect to have open at any one time, and add up their flow rates. This is the desired flow rate for the demand water heater. Select a manufacturer that makes such a unit. Most demand water heaters are rated for a variety of inlet water temperatures. Choose the model of water heater that is closest to your needs.
As an example, assume the following conditions: One hot water faucet open with a flow rate of 0.75 gallons (2.84 liters) per minute. One person bathing using a shower head with a flow rate of 2.5 gallons (9.46 liters) per minute. Add the two flow rates together. If the inlet water temperature is 50° F (10° C), the needed flow rate through the demand water heater would need to be no greater than 3.25 gallons (12.3 liters) per minute. Faster flow rates or cooler inlet temperatures will reduce the water temperature at the most distant faucet. Using low-flow showerheads and water-conserving faucets are a good idea with demand water heaters.
Some types of tankless water heaters are thermostatically controlled. They can vary their output temperature according to the water flow rate and the inlet water temperature. This is useful when using a solar water heater for preheating the inlet water. If, using the above example, you connect this same unit to the outlet of a solar system, it only has to raise the water temperature a few degrees more, if at all, depending on the amount of solar gain that day.
Demand water heaters cost more than conventional storage tank-type units. Small point-of-use heaters that deliver 1 gallon (3.8 liters) to 2 gallons (7.6 liters) per minute sell for about $200. Larger gas-fired tankless units that deliver 3 gallons (11.4 liters) to 5 gallons (19 liters) per minute cost $550-$1,000.
The appeal of demand water heaters is not only the elimination of the tank standby losses and the resulting lower operating costs, but also the fact that the heater delivers hot water continuously. Gas models with a standing (constantly burning) pilot light, however, offset some of the savings achieved by the elimination of tank standby losses with the energy consumed by the pilot light. Moreover, much of the heat produced by the pilot light of a tank-type water heater heats the water in the tank; most of this heat is not used productively in a demand water heater. The exact cost of operating the pilot light will depend on the design of the heater and price of gas, but could range from $12 to $20 per year. Ask the manufacturer of the unit how much gas the pilot light uses for the models you consider. It is a common practice in Europe to turn off the pilot light when the unit is not in use.
An alternative to the standing pilot light is an intermittent ignition device (IID). This resembles the spark ignition device on some gas kitchen ranges and ovens. Not all demand water heaters have this electrical device. You should check with the manufacturer for models that have this feature.
3rd yr apprentice
24 Dec 2000 at 6:13 am #289379Harold KestenholzParticipant
If you are thinking about an instantaneous water heater, there are some shortcomings that have pervented their widespread use in North America. They have difficulty when delivering less than 1/2 gallon per minute because the fire does not turn down to the small demand. The control to do this is a frequent demand for repair or replacement. You will start a 100,000 btuh gas fire to get a pot of hot water for tea. The small diameter tubes lime up in hard water areas, so Europeans typically replace heat exchangers within five years. Europeans also have the manufacturer’s servicemen disassemble, clean, inspect and reassemble the unit yearly.
24 Dec 2000 at 11:19 pm #289380SylvanLMPParticipant
Hey Harold DON’T confuse Frank with FACTS
Remember BOTH of you are on my list and it IRKS me to see my members not agree.
Now Frank you did bring up some great points BUT unfortunately WE AMERICANS know HEATING and comfort levels as WE are the ENVY of the world so Listen to us ELDERS OK LAD LOL
Frank I am impressed with your knowledge regarding piping materials I am sorry to say your apprenticeship program puts ours to shame.
Having both Qualified for American AND Canadian plumbing as a Journeyman I am duly impressed with your codes and code officials.
The education your getting is 2nd to none.
Your more then welcome to bring this topic up on the PIPDL and lets shoot the breeze over it as it is interesting.
Harold lets GET him LOL
24 Dec 2000 at 11:50 pm #289381SylvanLMPParticipant
Since 1990, a tankless coil boiler has a minumum AFUE of 80%. Most are rated higher than the minimum. When NEW and properly maintained and serviced
A water heater does not have that efficiency as it is a single-pass vertical heater. A tankless coil boiler with an input of 140,000 btuh, equal to a 1 gallon per hour nozzle
Hey not all # 2 “oils” are rated to 140,000 BTU per gallon some are rated to only 138,000 AND oil burners require lots of service to keep them in top operating condition Look at the stack temperatures you need to prevent a chimney from self destruction with oil fired equipment < ME
, can deliver 3 gallons per minute (180 gallons of hot water per hour.) When mixed with cold water it can produce 5 gallons per minute of shower water every hour of the day or all month if your budget allows.
Read your statement about “mixing water with cold” Think about this OK
Suppose a dude was to set his water heater to a temperature he/she needed just for showers and hand washing THINK of all the energy they save by NOT heating the water to dangerous high levels THEN cooling it down again? Same with Franks LOUSY System LOL
There is nothing else besides an external tank system that can deliver this, although an external tank can only produce this much in the first draw for the tank and far less for the following hours. WRONG IMHO
Suppose DURING the heating season you use the unfired tank as storage with a circulator back to the boiler NOW your using one burner for everything If you don’t like the unfired pressure vessel idea I had
f you buy another water heater instead of using the tankless coil system, you now have two heaters, one for the house and one for the hot water < NOPE
Not if you piped it in properly and valved it off in the summer months
– with two burners to service.< Harold, ME> OIL needs much more service then gas HOW often do you SERVICE your stove or over?
Now the boiler doesn’t have to stay warm for the summer months to make hot water, the extra water heater does < BUT Harold doesn't this Boiler have a larger mass to heat then a tank? PLUS Metal fatigue from cold to hot firing does take its toll ASK me about my ASME training in OU
– all year round. So which is better? – < Harold ME > Neither they BOTH have their draw backs this is NOT a perfect world
To have a tankless coil boiler weighing 360 pounds losing heat from the jacket during the summer (it is doing the heating during the other seasons), or a water heater weighing 350 pounds (including the water content) losing heat from the jacket all year round. < HAROLD > me> Suppose we compremise and go with a aa tank like an TROL that has a loss of about 1/2 a degree per HR if that much and use a SMALL VERY efficient boiler and use this tank with a copper coil as a separate zone calling for heat when needed YET having the firing rate to satisfy all water needs during peak demand and tell the Canadian KID where to go
I opt for a high efficiency tankless coil boiler set up with a mixing valve so there is only one heating appliance to service with only heat losses from one appliance instead of two, making more hot water than most people can use.< Harold >ME
Unless folks are going to use a GREAT Quality Mixing valve like HOLBY your looking for a failure and some scalding lawsuits.
Sending water through a system at 212+ in a closed system is not my idea of fun seeing it FLASH into steam AS an OSHA trained construction inspector for the plumbing industry board and United association of plumbers USA and Canada we kind of frown upon burning folks EVEN if some do deserve it.
Harold and Frank lets agree to disagree OK Keep these posts coming as its GREAT learning from BOTH of you North American folks
Ok Frank YOUR move Checkmate in 4 moves. I bid 7 NO TRUMP You go GUY
25 Dec 2000 at 4:07 am #289382Harold KestenholzParticipant
Of course he is going to use a quality mixing valve to lower the water temperature from the tankless coil. He wouldn’t think for one second to find the cheapest valve there was making hot water for his family. He wouldn
‘t want a scald for anyone. That’s why he wouldn’t select an instantaneous water heater with its varying water temperatures that can lead to scalds.
If he doesn’t want to settle for the greatest amount of hot water instantaneously as from a tankless coil, he can go to the external tank system which has proven to be more than satisfactory for homeowners. you would need a larger boiler than most to use a tankless coil boiler because the heat loss of a home would be that large in a house of 5000 square feet. An instantaneous water heater does not have the choice of a burner matched to the heatloss of the house, it must be large enough an input to qualify for heating a 4000 square foot house just to make some hot water.
With an external water heating tank, the water temperature could be set down to 120F with a recirculating system for instant hot water at the tap. The boiler could be sized for the heat loss of the house, so a small house could have a small boiler input to match the maximum efficiency while still getting all the hot water he needs from an external tank. He would be able to draw 2.4 gallons per minute for the shower or 1/2 a cup of water without turning on the burner for quite a while if the water had been sitting there warm already. If he needs more hot water, he can install another or a larger tank. Once he exceeds the amount of water he needs with the instantaneous unit, he would have to install another unit with its large input burner to provide more hot water.
Every heating system needs service and examination every year by a skilled, experienced plumber, so the frequency of service may be less for gas, but the frequency of examination must be the same – at least once per year for all these appliances.
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