4 Things to Check Before Installing a New, High Efficient Heating System.

I 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.

Thank you for stopping by Detect Energy, hope to see you again soon, but I won’t leave the light on for you...

More from Don Ames at www.detectenergy.com, visit Detect Energy and register for my free eNewsletter, the Energy Spy Insider.

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Tags: auditor, conservation, efficiency, energy, save, weatherization

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Comment by Jason Green on August 10, 2012 at 10:39am

I'm no professional, please excuse if this is the wrong place for this, but I've always wondered about insulating the duct work. If the heat is ultimately escaping from the duct work into the house, where is the loss occurring?

Comment by Emel Rose on July 18, 2012 at 9:56pm

You can go right to the duct work in just about any house and save the homeowner substantial money.  Ninety percent of more are undersized, let alone the shoddy sealing (as you pictured) leaky ducts etc.  Returns are generally too small, the AC system isn't performing it's best.

<a href="http://www.energyloadcalc.com">Energy Load Calc</a>

Comment by Ryan Schuchler on July 16, 2012 at 7:12am

Don, thank you for the informative article. The suggestions you've provided are great, and you really touched on a lot of points that most people wouldn't even think about without doing proper research. I found the section on "Room Air Balancing" to be particular interesting. As you mentioned, it's very important that that the warm or cold air inside your home doesn't escape through cracks between your window frames and walls. Another way to prevent this from happening is to make sure your windows are "custom-made." Some companies only make replacement windows in certain common sizes. They then cut or trim down the window frame to match up as closely as possible to the installation point. These are known as "custom-fit" windows. "Custom-made" windows, on the other hand, are manufactured to fit the exact dimensions of the point of installation, which eliminates any cracks or openings that could allow air to escape or enter your home. Thanks again for the helpful post Don!

Comment by Bob Blanchette on July 14, 2012 at 8:17am

Things are a bit different in the south:

In warmer climates going to a 96% from an 80% doesn't make financial sense, especially if the old furnace still works. Even when doing a replacement the extra $1,000 a 96% costs vs. 80% is going to have a 10+ yr payback time. What needs to happen on southern climates is smaller furnaces with large blowers. Selecting the smallest furnace you can buy with enough blower capacity for the A/C is proper way to do it down south.

Fixing ductwork problems makes a HUGE difference in the much more expensive cooling bills. Pulling in hot humid air has a bigger effect on A/C vs. Heat loss. In the south if you are replacing a furnace, might was well replace the A/C and "heat exchanger" (aka "A coil") at the same time. Down south you go through 2-3 condensers for every furnace replacement. Furnaces last 20-40 years, A/C about 10-15yrs.

Comment by Ralph Veluz on July 12, 2012 at 11:02am

good and simple ideas i specially like the cutting the bottom of the door to remove the pressure difference between rooms

Comment by Don Ames on July 7, 2012 at 8:08am

David,  Thank you for the comment. I really enjoyed your story about your own experience with the heating ducts. This is when a picture is worth a thousand words. It's important for people to hear this type of experience and see the pictures of failed heating ducts so they realize what can happen to ducts, how much energy they can waste, and that they need to visually inspect the duct system no matter how dark and dirty the crawl space is.

I am always interested in the results of energy saving retrofits - do they perform as well as they should. Unfortunately, the data needed a year later is not always available.

Thanks again,  Don Ames and detectenergy.com

Comment by David Martin on July 6, 2012 at 11:46pm

Say, Don, some financial data would be nice. You said the new furnace was $3800 installed. What about the additional measures you recommended? Do you have projections on what the homeowner might save?  Can you provide any utility bill data?  It would be interesting to see if your projections are in the ballpark after winter sets in.

By the way....

Before I agreed to purchase my house about 2 years ago, I had the previous owners install a new 95% gas furnace because the old one was not working.  They had the unit installed by a presumably reputable (I only say that because of they do a lot of work in my area) contractor of their choosing. I insisted that the ducts get inspected and serviced.  I was assured that the ducts were fine.  Being the trusting sort, I didn't check on their work until about 6 months or so later.  The pictures below are from the crawlspace, after I did a considerable amount of spider web removal and plumbing repairs.  A flexible copper drain line from the old water softener was resting on the rectangular galvanized ductwork.  The corrosion created small hole in the copper and a huge rusted out area in the duct that crumbled when I touched it.  As you can see the ducts are resting on the soil.  I cut a piece of sheet metal and duct taped it over the hole on the top.  Its okay because the dirt plugs the rust through in the bottom.

They must have overlooked this section, eh?

This experience has been a great motivator for me.  Once I get my energy efficiency business going, I am going to blow unscrupulous contractors like this guy out of the water.  I understand there are lots of them.

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