High Efficiency Condensing Gas Furnaces
February 11th, 2010
Even if you don’t subscribe to global warming, it’s good to conserve fuel to economical purposes as well as ecological ones. Gas prices are higher than they have been in a long time, and aren’t likely to become any cheaper. With the US having to import the vast majority of its natural gas, we are also dependent on others for supply, just like our oil.
The main issue for most consumers is that high efficiency furnaces cost more to buy than regular ones. They are more complicated, involve more manufacturing and cost more to make, and maintain. But, they pay for themselves many times over in the long run because they use much less fuel. Once a consumer gets over the higher initial outlay, high efficiency appliances make great sense.
An HVAC condensing gas furnace has two heat exchangers which extracts almost all the heat out of the burn. This process produces water, as natural gas is 5% water and the air it mixes with also contains water. Unlike older furnaces, a condensing one will pull air in from the outside to fuel the burn. It will then vent the gases out a separate vent. They also need a condensation drain to let the condensed moisture run off into the drainage system.
This use, then re-use of the resultant heat is how these gas furnaces can be rated at 90-95% efficiency. This is often expressed as 90plus or 95plus in sales literature. This is achievable because not only is all the heat from the burn used up, a second heat exchanger then extracts anything that’s left in the waste gases before venting them. Nothing is wasted in a condensing furnace as long as the water is left to run off into the drain.
The other main benefit is that you don’t need a pilot light running 24/7 burning gas all the time. The electronic ignition systems create a pilot on demand which turns off as soon as it isn’t needed any more. This saves a lot of gas over time, which only adds to the efficiency.
HVAC fuel efficiency is defined as the percentage of heat produced that is useable in the home. For example, a 90plus system would have 90% of its heat going directly into the home for the benefit of the occupants. The other 10% would be vented outside and wasted. Therefore, the higher the efficiency, the more value for money you’re getting each burn.
These condensing systems provide two problems. Firstly the condensed moisture needs somewhere to drain to, this is often the same as the air conditioning drain, but can be separate. The second is that the exhaust pressure is so low that it needs a fan to blow it out of the house. Neither problem was insurmountable, but both needed mechanical fixes which add to the cost of the unit.
Efficiency is key in everything we do and have. Overcoming the initial extra cost will allow you to reap the benefits later, especially if fuel prices continue to rise like they have been.