We had just completed a home energy audit and learned that insulation levels and air sealing measures were up-to-speed. After crawling into the attic, performing a duct blaster, checking the temperature of the hot water, and a bunch of other things, I had come to the educated conclusion that this home’s best chance for improved energy efficiency and lower energy bills while heating the house would include replacing the heating source.
The 80% gas furnace is in the garage right next to the gas water heater. The home is built on a sloping hillside so the ceiling in the garage is about 16 feet up. The furnace sits out-of-the-way under the stairs. It’s a down draft furnace with an Electric Air Cleaner sitting in the return air plenum over the furnace.
The Electric Air Cleaner has not worked in several years and the metal plates have been removed and replaced with 4 inch thick media filters. The door to the Air Cleaner opens facing the side wall of the garage. The wall is so close that the media filter must be cut into two pieces to manage the opening.
Removing this 26 year old furnace and installing a 96%, two stage, variable speed gas furnace should produce noticeable energy savings and lower heating and cooling bills. To get the most out of the $3,800 that the new furnace and installation will cost, there are a few things to check first before you start heating the house.
Number One – Heating Duct Air Leakage
Before installing the new furnace and allowing the new efficiently heated air to escape unused, the heating duct system should be checked for air leakage and then sealed as needed.
Numerous test homes have shown that sealing heating ducts is the most cost effective, energy saving, retrofit you can install. Do you need to have a pro with a Duct Blaster test your ducts and then have a duct sealing company seal them? Well, no, not exactly.
If your brother-in-law is an energy auditor with a duct blaster, invite him over. If your Power Company, gas or electric, has a duct sealing program, sign up. Your power provider may test your heating ducts for free. Otherwise, I suggest you handle the possible leaky duct system this way: Don’t test, just seal them. They probably need it anyway, and the more duct mastic the better.
If you have insulated flexible vinyl ducts, go ahead and check the connections where the flex ducts attach to the metal plenum or the metal register boots. Seal all the joints in the metal plenum and seal the boots to the floor. To seal the boots to the floor, you might need to have a hammer and some medium sized nails.
If you have metal ducts, whether they are round or rectangular, seal all the joints and connections with duct mastic. Remember, duct mastic can be applied with a gloved hand and works best when it’s applied nickel thick.
Duct sealing goes for both the supply and return air ducts. This means that you may need to spend some time in both the attic and the crawl space.
Remember, sealing the supply and return heating ducts is one of the most cost effective and successful retrofits you can do to your home that will save energy and lower energy bills.
Number Two – Room Air Balancing
Well, here’s a good one you might not of heard of before. The heating system is simply more efficient when it operates as a balanced system. That means, when the interior doors are closed, like they often are, the air pressure in each room should stay about the same.
If you have a bedroom door closed and the furnace comes on to warm the home and the warm air is forced into the room by the heating ducts and the air cannot get out of the room as fast as the heating duct is supplying the air, then you have a room with increased air pressure and you have a home that has lost energy efficiency.
The air that comes out of a heat register needs to find its way back to the return air duct system without having to squeeze through too many restricted channels.
As the pressure builds up in the room, the air you just spent money to heat up may find its way through the small draft hole between the wall and the window and end up being lost to the great outdoors. The higher the pressure, the more air is forced through the hole.
You can get a pretty good idea concerning air pressure in a room by conducting this do-it-yourself test.
◾Turn on the furnace or turn just the furnace fan on – if your thermostat will turn just the fan on.
◾Close the door to the room in question.
◾Light a stick of your favorite smelling incense.
◾Crack open the door until you can just peek into the room.
◾Hold the stick in front of the opening.
If the smoke blows back into your face like a Mack Truck just went by, you have a serious problem. If the smoke floats gentle back towards your face, you have a small, perhaps insignificant problem.
There is several good fixes that will add balance to the room air pressure. Consider one of the following:
◾Remove the door
◾Cut the bottom of the door off so there is a larger air passage between the door and the floor.
◾Install a pass through vent by cutting a rectangular hole through the wall over the door and installing a heating register over the hole on both sides of the wall.
◾Install an additional return air duct and register in the ceiling of the room and connect it to the return air plenum.
Anyway, if you’re installing a new high efficiency furnace and your rooms are not pressure balanced, you will lose some of that desired efficiency.
Number Three – Furnace Filter
Since the heating contractor will be making adjustments to the duct system that connects to the furnace, now is a great time to address the furnace filter.
Servicing the furnace filter is an important part of energy efficiency. Once the filter begins to restrict the flow of air, the furnace must work harder to accomplish the same heating and cooling results.
To have a filter that is in a location that is easy to get to is very important for ongoing maintenance. It is also important that the cabinet or plenum that holds the filter is easy to open and close.
Since you have scheduled the installation of a new high efficiency heating source, talk to the Heating Contractor about the filter and addressing any concerns at the same time. A good contractor may even throw in a little filter work for free.
Number Four – The Air Conditioner Heat Exchanger
If you have a gas furnace with whole house air conditioning, you have a heat exchanger sitting in the furnace duct work somewhere that connects to the outside air conditioning unit. It would make sense to me to have this heat exchanger accessible like the filter is, but most often, the exchanger is hidden away behind inaccessible sheet metal.
The heat exchanger looks a little like the radiator on a car. Thin, closely mounted fins, transfer the cool temperature to the passing air. The problem is the small channels of the heat exchanger can become clogged and then restrict the air from passing through.
Similar to a clogged filter, when the heat exchanger becomes clogged, energy efficiency is reduced. The furnace ends up working harder and longer.
While the Contractor has the old furnace removed and the plenum opened up, be sure the heat exchanger gets cleaned. If your heating system is 20 years old, I will guarantee you the exchanger needs cleaning.
Getting the most out of your new high efficient furnace is important if you are going to realize the energy and cost savings that are possible. To insure the efficiency you’re looking for, before you fire up the new furnace, check these four system items that affect how the new furnace will perform.
◾Check for heating duct leakage and seal up those leaks.
◾clean the air conditioner heat exchanger.
◾make adjustments to the filter and the filter cabinet.
◾add passages for return air that will balance the room pressure.
In the home that I spoke of at the beginning of the article that is getting the 96% efficient gas furnace, the filter cabinet was turned 90 degrees to increase accessibility, the heat exchanger was cleaned, the heating ducts were tested and found that leakage-to-the-outside was less than 200 CFM, and a new return air register was installed in the ceiling of the family room addition. With the new efficient furnace ready, it is now time to start heating the house.