By Cyril Courtois (RCM CAD Design Drafting ltd.)
Topic: Water heating options for your new home.
Heating water typically uses 10% to 25% of the overall energy spent to run your home, and is the second largest energy expenditure after heating and cooling.
Water heater options:
A/ Storage tank water heaters are by far the main choice in North America.
They are cheaply mass produced, and have an average life expectancy of 10 years, depending on your water quality.
Tank heating efficiency will go down due to sediment accumulation, and scaling on elements.
Five year warranty is the norm.
They run on electricity or gas, and most common tank capacity ranges from 40 to 60 gallons, but, can be up to 100 gallons depending on your family needs.
Although electric water heaters are cheaper to buy and install, gas heaters are much cheaper to run because electricity is much more expensive per BTU than gas.
If you have natural gas to your property, or propane gas delivery available, then it is well worth going with gas and spend more for installation (gas vent).
To improve water heating efficiency in your home…
1- Use less hot water by selecting low flow faucets and shower heads.
Bathroom faucet at 1 gallon per minute (GPM)
Kitchen faucet at 2 GPM
Shower heads at maximum 2 GPM
2- Turn down your water heater thermostat to 60 C (140 F), but no lower than 55 C (130 F) to avoid risk of bacteria.
This also slows mineral build up and corrosion thus increasing tank life expectancy at top efficiency.
3- Insulate all hot water lines and install insulating blanket on your tank.
4- Purchase an increased efficiency water heater or a condensing water heater for best performance.
Select electronic ignition instead of pilot light option to save energy for gas powered water tanks.
B/ Solar water heaters can save 50% or more of a home’s hot water expenses, even in the cloudy Pacific Northwest.
They are the most cost effective way to harness solar energy, since they absorb solar radiation, rather than just sunlight. Even in the cold winter months they can work as water preheaters in conjunction with a hot water system.
Most likely tax credits and grants are available for new homes and renovations in your area.
Solar collectors will require up to 6 m2 (65 ft2) of south facing roof space with minimal shading.
Evacuated tubes are best compared to flat plate solar collectors as (when mounted on a south facing roof slope), they are designed to track the sun from east to west.
Refer to diagram below.
Lifetime of this system ranges from 25 to 40 years and the installed cost start from $7000.00 for a family of four.
It will typically take 10 to 15 years to payback the investment.
C/ Tankless water heaters or, on demand water heaters, heat water when needed, thus eliminating stand by heat loss common to conventional water tanks which constantly store 40 or more gallons of hot water all year round.
Compared to hot water tanks, they are at least double the initial investment. Energy tax credits and grants are available in most regions.
However, they also last at least twenty years, double the lifespan of a conventional water tank. They also save energy, with the payback taking seven to fifteen years.
An added benefit is their small size, not much bigger than an electric panel, which means saving precious living space.
They are available as point of use (for each bathroom or kitchen sink and dishwasher), or they also come as larger units, or multiple units able to supply hot water to the whole house…
Beside the energy savings, their main attraction is that they can provide hot water endlessly. No more running out of hot water in the middle of a shower!
As with conventional water tanks, there are two main energy sources:
Electric powered tankless heaters demand large amount of electricity to run at peak demand time of the day.
Some local power companies do not allow them as they draw so much power at peak consumption time (eg. showering in the morning).
Gas powered tankless heaters make much more sense, as both natural and propane gas are much cheaper to run them.
However, remember that choosing gas means you need to
vent the unit, so it will need to be placed on a perimeter wall for direct venting, or otherwise a chimney will be required for central locations.
Sizing your tankless unit to your needs is an important step before buying. There are two main things that you will need to know: The flow rate and the temperature rise.
You will need to calculate the amount of water the unit must heat by measuring the flow rate in GPM of every faucet, appliance, shower and bath it is connected to.
You need to know the temperature of the cold water before it enters the tankless heater, and how hot you wish the water to be when it comes out. The difference between the cold and hot water is the temperature rise. The cold water coming to your house from the city, or well is dependent on location of your property.
When you know the flow rate and temperature rise required, a properly size heater can be selected to maximize energy savings and ensure desired hot water temperature at the tap.
D/ An interesting and inexpensive way to reduce the temperature rise, is to install a drain water heat recovery heat exchanger to raise the temperature of incoming cold water.
Typically, 80% or more of the energy used to heat your home’s hot water goes down the drain when you take a shower, bath, use the dishwasher or wash your clothes. A grey water heat recovery system will preheat the cold water entering your water heater by using a simple heat exchanger as shown in diagram.
It requires no power to run and has no moving parts.
The cost of this system ranges from $400 to $700 depending on length of heat exchanger and diameter of the vertical copper drain pipe which the cold water pipes are coiled around.
Of course the fresh incoming water does not mix with the drain water at any time.
You can expect about 20% savings or more on hot water heating cost and payback is three to four years.
Energy costs are high and will continue to rise relentlessly.
As you are planning to build a new home, I recommend you research all available options to save energy.
We all need hot water for our home use, but at what cost?
Solar water heating technology is beginning to make more sense than ever, and solar energy is free. Payback time on that investment will continue to get shorter, as energy costs keeps on rising.
Tankless gas water heaters are a great fit with solar systems as they bring the water to desired heat level in the cold winter months.
Drain water heat recovery is a simple technology that works well with both solar and tankless systems to maximize your energy savings for your hot water needs.