Tankless Water Heater: Endless Hot Water or Shameless Hype
Tankless Water Heater Claims
Tankless Water Heaters have become a really hot topic in the last couple of years (I know, that was a really bad pun). The claims range from "endless hot water" to huge savings on home energy bills. It almost sounds too good to be true, like just more of the marketing hype we've all become used to. Are tankless water heaters really the best thing since sliced bread or just another passing fad? The answer may depend on how you use hot water.
How Can Higher Efficiency Equal Higher Gas Bills?
It is certainly true that tankless water heaters, technically speaking, really are more efficient than most tank type water heaters, even if the manufacturers' claims might be a little optimistic. Their higher efficency comes from not having to use any energy keeping a tank full of stored water hot. That would seem to make it a no-brainer that a tankless will save money on energy bills. In spite of this, some people have actually reported higher gas bills after installing a tankless.
The World's Longest Shower
The reason that some people don't see any actual energy savings with a tankless heater is actually due to one of the stated benefits of tankless: endless hot water. That's right, some people actually see their gas bills go up because more hot water is being used since there's more available now. (This phenomena has been reported to be linked with the presence of teenage girls but there is no scientific data to support this yet.) Showers that used to be cut short by the hot water running out can now be extended virtually indefinitely. So if you want to go tankless to save money you should be aware that this is a possible issue.
Endless Hot Water?
That brings us to the other big sales pitch for tankless water heaters: endless hot water. Can that really be true? No more cold showers after the tub has been filled or the laundry has been going all day? Well, yes...with a few restrictions.
Temperature vs. Volume
Since almost all tankless heaters are designed to maintain a desired outlet temperature, they have to restrict the flow through the heat exchanger to do so. This means that there is a limit to how much hot water they can provide at a given temperature rise or "Delta T". Basically, if you try to use more hot water at one time than the heater can provide it will limit the output volume to maintain the desired temperature. This could leave you in the shower, with shampoo in your hair, thinking you have been suddenly teleported to a cheap hotel.
Sizing Is Important
The good news is that this problem can be avoided by properly sizing the tankless water heater and, in some cases, by using more than one heater. The bad news is that tankless water heaters are fairly expensive and two will probably cost, yep, twice as much as one. I don't, however, want to make the issue sound bigger than it is. Most 2-3 bath houses will be just fine with one properly sized tankless water heater. If you have more than 3 baths or showers and expect them to all be used at the same time, or if you have a master shower with lots of body sprays and extra shower heads, you will probably need at least two units.
Figure Your Demand
It's pretty simple to do the math. Just figure 2.5 gallons per minute for each shower head and 1 gallon per minute per each body spray. Check the literature for the brand heater you are considering and find the output in gallons per minute (GPM) at the temperature rise you need. A 60 degree rise will cover most situations, find out your winter cold water temperature. Make sure you will have enough flow volume to meet your needs from one unit. If not you will need two. These figures are pretty close for tubs and showers less than 10 years old, if your's are older it is a good idea to measure how much water they are putting out. Just use a bucket and a watch with a second hand.
Take A Look At Your Lifestyle
The main lesson here is that it is important to take a good look at your hot water usage habits when you are trying to decide on tankless. This will help you to find out if you would have to make any compromises in your lifestyle to take advantage of the benefits of a tankless water heater. They really are more efficient and as long as you don't start taking super long showers a tankless should save you money.
Copyright 2008 Bryan Stevens
Tankless Water Heaters have become a really hot topic in the last couple of years (I know, that was a really bad pun). The claims range from "endless hot water" to huge savings on home energy bills. It almost sounds too good to be true, like just more of the marketing hype we've all become used to. Are tankless water heaters really the best thing since sliced bread or just another passing fad? The answer may depend on how you use hot water.
How Can Higher Efficiency Equal Higher Gas Bills?
It is certainly true that tankless water heaters, technically speaking, really are more efficient than most tank type water heaters, even if the manufacturers' claims might be a little optimistic. Their higher efficency comes from not having to use any energy keeping a tank full of stored water hot. That would seem to make it a no-brainer that a tankless will save money on energy bills. In spite of this, some people have actually reported higher gas bills after installing a tankless.
The World's Longest Shower
The reason that some people don't see any actual energy savings with a tankless heater is actually due to one of the stated benefits of tankless: endless hot water. That's right, some people actually see their gas bills go up because more hot water is being used since there's more available now. (This phenomena has been reported to be linked with the presence of teenage girls but there is no scientific data to support this yet.) Showers that used to be cut short by the hot water running out can now be extended virtually indefinitely. So if you want to go tankless to save money you should be aware that this is a possible issue.
Endless Hot Water?
That brings us to the other big sales pitch for tankless water heaters: endless hot water. Can that really be true? No more cold showers after the tub has been filled or the laundry has been going all day? Well, yes...with a few restrictions.
Temperature vs. Volume
Since almost all tankless heaters are designed to maintain a desired outlet temperature, they have to restrict the flow through the heat exchanger to do so. This means that there is a limit to how much hot water they can provide at a given temperature rise or "Delta T". Basically, if you try to use more hot water at one time than the heater can provide it will limit the output volume to maintain the desired temperature. This could leave you in the shower, with shampoo in your hair, thinking you have been suddenly teleported to a cheap hotel.
Sizing Is Important
The good news is that this problem can be avoided by properly sizing the tankless water heater and, in some cases, by using more than one heater. The bad news is that tankless water heaters are fairly expensive and two will probably cost, yep, twice as much as one. I don't, however, want to make the issue sound bigger than it is. Most 2-3 bath houses will be just fine with one properly sized tankless water heater. If you have more than 3 baths or showers and expect them to all be used at the same time, or if you have a master shower with lots of body sprays and extra shower heads, you will probably need at least two units.
Figure Your Demand
It's pretty simple to do the math. Just figure 2.5 gallons per minute for each shower head and 1 gallon per minute per each body spray. Check the literature for the brand heater you are considering and find the output in gallons per minute (GPM) at the temperature rise you need. A 60 degree rise will cover most situations, find out your winter cold water temperature. Make sure you will have enough flow volume to meet your needs from one unit. If not you will need two. These figures are pretty close for tubs and showers less than 10 years old, if your's are older it is a good idea to measure how much water they are putting out. Just use a bucket and a watch with a second hand.
Take A Look At Your Lifestyle
The main lesson here is that it is important to take a good look at your hot water usage habits when you are trying to decide on tankless. This will help you to find out if you would have to make any compromises in your lifestyle to take advantage of the benefits of a tankless water heater. They really are more efficient and as long as you don't start taking super long showers a tankless should save you money.
Copyright 2008 Bryan Stevens
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