Replacing an Oil Furnace

Our old oil furnace must have been the original furnace installed when the house was built in 1978. Last winter I had to periodically tap the burner with a stout object to get it to run. I was hoping to upgrade to a high efficiency gas heater, but the gas pipe on our street is a transmission pipe, not a gas main. The gas company said no. So weighing options (propane, electric, heat pump, oil), I decided to get a new oil furnace. The other options are more expensive than oil, even now in 2011.

As I always caution: don't try this at home! If you play with fire, you will get burned, or you will die of asphyxiation. Let's face it, I am reasonably handy or I wouldn't be able to do all the cool stuff I do. There! I said it!

Out with the Old

Here is the old furnace:

Here is the information plate above the burner:

The output of the old furnace was 85,000 BTU. The furnace was able to heat the house on the coldest days of the year, so I will replace the old furnace with one of similar output. I will go a little lower because I am hoping to supplement oil heat with radiant electric heat provided by our solar panels.

To remove the old furnace, I had to cut away some of the duct above the furnace:

I drilled out rivets where I could get at them with a power drill:

I had to cut some of the cold air return duct at the bottom where I could not get to the rivets (not shown). I disconnected all the wires to the burner. Here are the thermostat wires before I took them off:

I thought this picture might help me later. It didn't.

I attached some lumber above the furnace to support the air ducts and the A-coils for the air conditioner. I used a rope on the right side and yellow tie-down strapping on the left to hold up the A-coils. You can see the A-coils peeking out through the separated duct sheets:

Now the furnace could be removed:

Furnace out of the basement:

In the garage:

In with the New

I got the new furnace, a Comfort-Aire OUFA75-D3, from Alpine Home Air. They had a great price, free and fast shipping. I slid the new furnace into position. I had to put temporary wood shims under the furnace to get it to the right height under the upper air duct:

Air Ducts

With the furnace in this position, I was able to line up and measure where the cold air return duct would meet the new furnace:

At this point I knew I couldn't easily use the old cold return elbow, so I made some drawings:

I took these drawings to MC Metal in Berlin, NJ. They made the return elbow for me for $48 plus tax. Thanks, MC Metal. Here it is, complete with S cleats and drives to connect it to the old cold air return duct:

The furnace came with a filter rack (and filter) shown on the end of the elbow in this picture:

Before attaching the elbow to the furnace, a big rectangular hole had to be cut in the side wall of the furnace. The fact that there is no hole is a selling point for the furnace: the cold air return can be installed on either side! Lucky! Lucky me! There are marks to show where to cut:

I marked the lines with a marker using a carpenter's square. This is not the lair of one of Batman's arch-foes. I have tilted the furnace back so I can more easily work on it:


The basement smelled like fireworks for the next several hours. Here is the hole:

I needed to raise the furnace about an inch higher than the old furnace. I got bricks at Home Depot for permanent support. Then I moved the furnace back in place under the old duct.

To remove the old return elbow, two "drives" had to be removed. This is a drive:

Bend the tabs:

Pull it off:

Then the elbow falls off:

I put the new one on, only having a little trouble with one of the long sides, wiggling it into the "s-cleats." This picture shows the new elbow after I screwed it to the furnace with sheet metal screws.

The upper air duct, called the plenum, had to be repaired. I measured and marked a piece of sheet metal that will become a patch for the plenum:

I shaped it with a rubber hammer:

And welder's pliers:

I trimmed it, mounted it in place, secured it with sheet metal screws on each side:

I taped it with HVAC metal tape to seal it:

The Flue

The exhaust outlet diameter of the new furnace is 6 inches. The pipe into the chimney was only 5" in diameter:

The old mortar and the pipe were not difficult to remove, fortunately:

This hole is about 6.5" wide and will accommodate the new flue.

I built the flue. Here is a time lapse version:

It is fitted together here, not finished yet:

The flue must have a draft control. It came with the furnace but it has to be spliced into the flue pipe.

Mark the hole:

Cut out the hole and cut tabs (you can also see in this picture that I have also mortared a pipe into the chimney):

Install the draft tee:

Bend the tabs up to seal the hole, insert butterfly valve. In this picture, I have also fastened the pipe sections together with sheet metal screws:

I was reminded of the tin man as I built the flue. There is your Wizard of Oz reference for the day.

Oil Line

I changed the oil filter under the oil tank. It was just as messy as changing the oil filter on a car.

Recommendations are to install a "Firematic" valve before the burner. This valve will shut (by means of a melting lead pellet) if there is a fire. When I called to schedule a service call, the oil company said they would drop off a valve for me to install. Nice.

To insert the valve, I cut the old supply line about a foot off the floor:

I had to buy a couple of small cheap tools for the next step. I got a flare tool so I could attach the valve, and a tubing bender so I could bend the copper supply line without crimping it.

Here is the flare tool in action. This tool flares the end of the copper pipe so it will seal against a flare nut:

A bit blurry, a flared end:

Here is the valve, with flare nuts on either side. I flared both the upper and lower pipes and screwed on the flare nuts hand tight:

I bent the remaining tubing to meet the new burner. Screwed on the flare nut. The tubing bender is also shown:

I tightened all the flare nuts after fitting everything together.


I hooked up the wires according to the wiring diagram on back of the cabinet door:

The thermostat wires are color coded. Cyan wire to C, yellow to Y, Green to G, red to R. white to W. The bigger black and white wires in the upper right box go to house AC and there is a ground screw for the ground wire. I wired the AC to the old ON/OFF switch (not shown).

Ready for the oil guy. I wanted a professional to tune the burner. I don't have any tools to do that. I also wanted a professional to check my installation, and I wanted to watch what he did so I could understand my furnace better. He arrived, looked at what I did, said everything looked good. He bled a lot of water out of the oil tank; the empty tank had been recently filled. He changed the nozzle at my request (0.65 instead of 0.50) and said he would have recommended a bigger nozzle also. The small one will clog. He checked the wiring, said the old thermostat wiring didn't quite match. I said I had a new programmable thermostat that I was going to install soon so he did it for me, to make sure the wires matched. He started the furnace after a second bleeding, tuned it with his smoke tester, let it run a bit. Done. I have a new furnace:

October, 2011