The two systems used for heating hot water are water heaters that store a volume of pre-heated water and tankless hot water on demand systems which heat and supply hot water when you require it.
Lets look at tankless hot water on demand heaters and some of the things you need to consider prior to making your final purchase decision.
Because the water is being heated instantaneously, there are a number of important issues that need to be considered before and during system selection:
1. What is your energy source?
On demand hot water systems are power hungry. They need to heat water quickly and this takes large quantities of energy depending on their flow capacity. Hot water on demand systems can be powered by electricity, town gas or bottle gas - Propane. So the first consideration is: Does your home have the sufficient energy available? Gas should not be a problem, but it's worth getting your gas meter's flow capacity checked.
Using electricity gets more critical; you should get your power board checked to make sure you have the energy capacity to run an electric tankless hot water heater. The power requirements of these systems can be high so before you buy, get an electrician to make sure your power board can cope with the extra load, this will save you a lot of potential problems.
You will need a dedicated circuit and circuit breaker for your tankless heater as loads can be 40 amps and above.
2. How many faucets will the system be supplying?
Different outlets have different flow rates, some have small flows and others much larger. Spending some time working this out will not only influences your choice of heater but also help you determine if you are going to need multiple tankless heaters. This is not so critical for a single outlet but very important is your tankless hot water system is going to supply multiple outlets. I don't thing you want your shower running cold if someone turns on another tap.
So spending the time working out what temperature rise - flow capacity your heater is going to have to provide, is pretty critical to getting it right first time. You may find that a single tankless hotwater heater won't be able do everything and you are going to have to install multiple units.
Here are some average flow rates in gallons per minute for different outlets and appliances:
You can see from this that there is a lot of variability, so if you are planning on having your on demand water heater supply several outlets you need to get the flow volumes right.
3. Where are you mounting your on demand water heater?
If you are using an on demand gas water heater, you need to consider how you will vent the exhaust gas if you're installing the heater is indoors. This can be up and out through the roof or through the wall, but either way, the exhaust gas must be vented to the outside. The ducting be straight forward, or it could be complex and costly, the bottom line is you do not want the exhaust gas which contains CO, (carbon monoxide) to remain inside your home.
Electric tankless hot water heaters are much more straight forward as there are no fumes so can be mounted inside or out.
4. Distance from Faucet:
The longer the pipes the more heat loss you can experience, plus you waste more water before the hot water arrives. To get the most efficiency from your on demand water heater it's probably best to have one per bathroom. They will be smaller so use less power and can be sized to suit each bathroom. Being close to the bathroom, the pipe runs are short so very little water is wasted.
This setup is best done a build stage so the plumbing is installed to suit and the total demand energy requirements can be calculated. Up front costs might be slightly higher, but the energy savings are significant in the end.
5. Temperature Rise Ability:
Every manufacturer of on demand water heaters quote their temperature increase ability for a particular flow rate. Here is an example for one particular water heater; the Stiebel Eltron Tempra 24 Operating at 208 volts, 18 kw with a water inflow temperature of 50 F.
Outlet Temp   105 F  113 F  125.6 F
Flow in GPMÂ Â 2.27Â Â Â Â 1.95Â Â Â Â 1.62
This illustrates how important it is to size your on demand water heater to your needs. If you don't you will find yourself having insufficient hot water to run multiple outlets or to run a specific appliance.
So spend some time doing the basics, working out your requirements and your energy availability and you will never run out of hot water.
Lets look at tankless hot water on demand heaters and some of the things you need to consider prior to making your final purchase decision.
Because the water is being heated instantaneously, there are a number of important issues that need to be considered before and during system selection:
1. What is your energy source?
On demand hot water systems are power hungry. They need to heat water quickly and this takes large quantities of energy depending on their flow capacity. Hot water on demand systems can be powered by electricity, town gas or bottle gas - Propane. So the first consideration is: Does your home have the sufficient energy available? Gas should not be a problem, but it's worth getting your gas meter's flow capacity checked.
Using electricity gets more critical; you should get your power board checked to make sure you have the energy capacity to run an electric tankless hot water heater. The power requirements of these systems can be high so before you buy, get an electrician to make sure your power board can cope with the extra load, this will save you a lot of potential problems.
You will need a dedicated circuit and circuit breaker for your tankless heater as loads can be 40 amps and above.
2. How many faucets will the system be supplying?
Different outlets have different flow rates, some have small flows and others much larger. Spending some time working this out will not only influences your choice of heater but also help you determine if you are going to need multiple tankless heaters. This is not so critical for a single outlet but very important is your tankless hot water system is going to supply multiple outlets. I don't thing you want your shower running cold if someone turns on another tap.
So spending the time working out what temperature rise - flow capacity your heater is going to have to provide, is pretty critical to getting it right first time. You may find that a single tankless hotwater heater won't be able do everything and you are going to have to install multiple units.
Here are some average flow rates in gallons per minute for different outlets and appliances:
- Toilet Sink: 0.5 - 1.5 gpm
- Bath Tub: 1.5 - 3.0 gpm
- Shower: 1.5 - 3.0 gpm
- Kitchen Sink: 1.0 - 2.0 gpm
- Washing Machine: 1.5 - 3.0 gpm
- Laundry Tub: 2.5 - 3.0 gpm
- Dishwasher: 1.0 - 3.0 gpm
You can see from this that there is a lot of variability, so if you are planning on having your on demand water heater supply several outlets you need to get the flow volumes right.
3. Where are you mounting your on demand water heater?
If you are using an on demand gas water heater, you need to consider how you will vent the exhaust gas if you're installing the heater is indoors. This can be up and out through the roof or through the wall, but either way, the exhaust gas must be vented to the outside. The ducting be straight forward, or it could be complex and costly, the bottom line is you do not want the exhaust gas which contains CO, (carbon monoxide) to remain inside your home.
Electric tankless hot water heaters are much more straight forward as there are no fumes so can be mounted inside or out.
4. Distance from Faucet:
The longer the pipes the more heat loss you can experience, plus you waste more water before the hot water arrives. To get the most efficiency from your on demand water heater it's probably best to have one per bathroom. They will be smaller so use less power and can be sized to suit each bathroom. Being close to the bathroom, the pipe runs are short so very little water is wasted.
This setup is best done a build stage so the plumbing is installed to suit and the total demand energy requirements can be calculated. Up front costs might be slightly higher, but the energy savings are significant in the end.
5. Temperature Rise Ability:
Every manufacturer of on demand water heaters quote their temperature increase ability for a particular flow rate. Here is an example for one particular water heater; the Stiebel Eltron Tempra 24 Operating at 208 volts, 18 kw with a water inflow temperature of 50 F.
Outlet Temp   105 F  113 F  125.6 F
Flow in GPMÂ Â 2.27Â Â Â Â 1.95Â Â Â Â 1.62
This illustrates how important it is to size your on demand water heater to your needs. If you don't you will find yourself having insufficient hot water to run multiple outlets or to run a specific appliance.
So spend some time doing the basics, working out your requirements and your energy availability and you will never run out of hot water.
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