A condensing storage water heater uses a condenser to increase the efficiency of a traditional storage water tank. These models achieve a higher efficiency than a conventional tankless water heater does, but still offer the benefits of a storage tank water heater. These tanks have a fan that directs air and fuel into a sealed combustion chamber. The exhaust gas from the combustion chamber is forced through a secondary heat exchanger located inside the tank. The secondary heat exchanger delivers the “waste heat” from combustion back to the water in the tank, increasing its efficiency.
Like a condensing tankless system, the heat exchanger is so effective at cooling the exhaust gases that they can be vented to the outside using common PVC materials. The thermal efficiency of a condensing storage water heater typically exceeds 90% – far better than your current conventional tank, and it avoids some of the problems that tankless systems may have.
Condensing storage water heaters have the same footprint as a conventional storage tank heater does, so they work well as replacements. Since they already have an exceptionally high efficiency rating, they already meet the new required standards. Some condensing storage tank water heaters can use an existing ½” gas line. Larger tanks usually require a larger service line. Depending upon the model you choose, you may or may not have to re-plumb your gas service.
Condensing storage tank water heaters require a 120-volt electrical service to run the fan. The fan will produce some noise when it is operating, and you may hear this in your home’s living space. Additionally, you cannot use your existing flue to vent the remaining gases to the chimney, but a new, PVC exhaust flue is inexpensive and the exhaust run can be as long as needed to reach an outside wall.
One additional twist is that you’ll need a condensate drain for your condensing water heater. A condensing storage water heater produces condensation that collects in the flue and heat exchanger. This condensation is trapped inside the tank and drains to the outside of the tank. The condensate is acidic enough to cause damage to metal, concrete and other surfaces, so it can’t just be dumped down the drain. Condensing storage water tanks have a neutralizer cartridge filled with limestone or another base material, and the condensate is forced through this cartridge before it is drained away. The neutralizer cartridge needs to be checked annually and replaced or refilled when the neutralizing medium deteriorates.
Condensing storage water tanks, which were designed initially as commercial appliances, cost about twice as much as a conventional tank. While that may seem high, a condensing storage water tank has a life expectancy of about 10-15 years. With the lower operating costs and lower installation costs, a condensing storage water tank may be the right option for you. As an added bonus, throughout 2015, Gas Networks customers can take advantage of a $500 rebate on the purchase of a gas-fired condensing water heater with an efficiency rating of .95 or better.
If you’re considering the installation of a condensing storage water heater, please contact us at Boston Standard Plumbing & Heating at (617) 288-2911 anytime. We can explain the benefits and costs associated with condensing storage water heaters, and help you make the best choice for your home.