Tankless Hot Water Heater Overview
Tankless water heaters are a relatively new way to provide domestic hot water to a home. Sometimes called on-demand or continuous water heaters, tankless units are designed hot water when and only when it is called for. According to the Propane Education and Research Council, tankless water heaters, especially those fueled by propane, save energy and water and emit fewer greenhouse gases than conventional storage type electric water heaters.
Of course, savings vary by household use, local utility rates and other factors. Still, many contractors aren’t sure how tankless water heaters work and might be a little sceptical about their performance claims. To answer those questions, let’s take a look at how a tankless heater compares to a storage water heater by looking at the guts of both products.
Let’s look at conventional water heaters first. Residential storage type water heaters use an insulated tank, usually about 40 gallons in capacity.
The water in the tank is kept heated at all times for delivery, so the unit is always on and using energy, albeit at a very slow rate, to maintain water temperature within about 10 degrees of the unit’s thermostat setting. The main water supply enters from the top of the tank, a dip tube extends that line to the lower section of the tank.
When hot water is called for inside the house, the water in the tank begins to flow through the home’s plumbing system, through a second pipe at the top of the tank.
A separate chamber below the main tank contains the unit’s heating element, which is controlled by a thermostat or for natural gas and propane units, a burner control. As the hot water in the tank is exhausted, the burner below ignites to heat incoming freshwater.
Little or no hot water is available during this recovery time. Storage water heaters provide a relatively low installed cost, a variety of sizes to serve large and small homes, and respectable flow rates to deliver domestic hot water.
Because of its size, however, the storage water heater is usually located in a home’s utility closet or garage, not always a centralised location within the home’s floor plan. As a result, delivering hot water through the home can take a few minutes, a condition called lag time that all water heaters experience to some degree. This lag time, though, wastes several gallons of unused water and can be inconvenient for the owners.
Now, let’s take a look at a tankless water heater.
These units use a compact metal cabinet instead of a tank. Because there’s no pre-heated or standby water to manage, there’s no need to insulate the cabinet or maintain a level of heat or heating energy. So, instead of being always on, a propane tankless heater only uses energy when there is a demand for hot water.
Otherwise, it’s effectively off. That difference accounts for the bulk of energy savings and reduced emissions afforded by tankless water heaters. When hot water is called for by an appliance or a faucet, cold supply water flows into and through the unit. A sensor detects the flow, triggering a computer generated signal to send propane to the heating element and bring combustion air into the inducer motor.
This exterior unit draws combustion air from the intake at the top and exhausts it from the louvred vent near the bottom. Units installed inside require a sealed combustion direct vent pipe that both brings in and exhausts combustion air safely from and to the outside. The flow of propane triggers the burners to ignite, warming the heat exchanger. These pipes curl around and through the exchanger, heating the water as it flows.
The heated water is then delivered through the home’s plumbing system to the appliance or faucet being used. This process enables a tankless water heater to deliver an almost unlimited amount of hot water, even if more than one hot water using appliance or fixture is on at a time. And once the tap is turned off, so does the unit and its energy demand and related energy cost. The space-efficient design of tankless heaters enables them to be placed strategically throughout the house and even outside to greatly reduce lag time and the amount of water wasted in that process.
Before we conclude this insider’s view into domestic water heating, here are a few quick tips for choosing and installing a propane fueled tankless water heater:
- Size the unit for the home’s specific hot water needs.
- Provide adequate capacity for the water supply and delivery network.
- Oversizing a unit actually works against the advantages of a tankless water heater.
- If the home has a lot of needs consider multiple units and dedicated plumbing to ensure their performance.
- Installation is relatively simple, similar to a storage heater and should be performed by a professional plumbing contractor.
- The water supply line typically connects to the bottom of the tank as does the delivery or outgoing line.
- On this exterior unit, the dedicated line for propane also connects at the bottom of the cabinet.
- The unit also requires electricity and control wiring to operate its electronic components.
- For any type of water heater, it also is a good idea to treat any water source that’s mineral rich or a poor quality. Doing so extends the life and performance of the unit.
We at the Propane Education and Research Council hope that this video has provided you with greater insight and assurances about tankless water heaters. Fueled by propane, tankless water heaters are an increasingly viable option for builders to help distinguish their homes as efficient and convenient.
They save money, energy and water while helping reduce harmful greenhouse gas emissions. Tankless water heaters also deliver greater convenience and comfort for homeowners and can be a key element in securing a home sale or remodelling contract. We encourage you to check out the efficiency ratings, now available among leading brands of tankless water heaters by the Federal Energy Star program at energystar.gov and consider federal, state and local utility tax credits, rebates and other financial incentives available to builders and homeowners who specify tankless units for their new and remodelled homes. For more information about tankless water heaters and the benefits of using propane to create more comfortable homes from the inside out, please go to buildwithpropane.com or call the Propane Education and Research Council.