Monday, January 22, 2007

Adventures in Heating - Part 2

With all the radiators installed and piped into the system it was time to focus on the boiler. It's an old H.B. Smith coal boiler that was converted to oil. It was in serious need of maintenance and cleaning. I almost considered replacing it, but after talking to my buddy John who worked in heating back in the day, he said it was a keeper. When I first told him about it, he was expecting to see some asbestos covered octopus unit - but instead he said these were one of the best ever made. H.B Smith was mostly an industrial boiler maker and that in it's day these were the Cadillac in boilers, and actually are still in business to this day. So it was decided to give it an over hall and see what happens.

The oil burner was fitted into the old ash door and the opening filled with a heater cement - can't recall the name of it. It was shabby installation, but got the job done. The old sight glass had been covered with the same stuff. There was no filter on the oil line which also was a problem. The old supply and return pipes were originally covered in asbestos insulation, but this was long removed leaving bare rusty pipes that heated the basement more than the house. The boiler was disassembled down to the cast iron water tubes and the process of restoring/repairing began.

The panels were repainted. The cast iron front door assembly was sandblasted, repainted, the original sight glass repaired, and gaskets added to the doors. Some vent holes from its coal days were sealed to stop any unwanted drafts through the boiler. The cast iron exhaust elbow had a crack repaired and an early unused damper sealed and new plate made for back cover. The expansion tank was flushed and repainted. I repacked the original valves, went over the old gauges and rewired everything. Most important, I added a local emergency disconnect on the side of the boiler and at the top of the basement stairs - both must be in the on position for boiler to operate.

With the main boiler reassembled and thoroughly cleaned inside, next was the oil burner. It's a Beckett burner, the Chevrolet of oil burners. I went through a complete rebuild making it like new condition. The tip was OK which I cleaned and reused - I wish I had noted the size as you'll see later though. With the burner done I needed to come up with a better mounting solution. My dad and I came up with a design and he fabricated it out of stainless steel plating. It's basically a big L, with a base plate with lock downs to hold the burner and a vertical plate that covers the opening of the boiler with a hole to allow the burner to poke through. Everything is sealed with high temp gaskets. An in line filter was then added and the assembly installed.

With everything fitting together as designed, the front disassembled one more time to install a new firebox, which was in desperate shape. I found a universal one on EBAY that worked perfect. I was able to center the new one better inside the boiler with just the tip of the burner entering. You don't want the flame to close to the back wall of the firebox which will disrupt the flame pattern.

Old and new fireboxes

So I'm sure at this point you're saying Hey, great, now it's nice looking ancient oil hungry beast. Well you'd be surprised. The paperwork with the boiler had the burner measured in the mid 80% range. But, then there's the efficiency of generated heat and transfer of that to the system?? Yes, I thought of that too. The biggest problem with these old coal units is you have this huge firebox that you throw heat into, which quickly is drafted into the flue and up your chimney taking probably 50% the heat you just made with it. So the question is, how do modern boilers slow this down and increase the transfer? Well one of the main ways is adding baffles, creating a "torturous path"for the heat and gases. Basically the longer the heat and gases created by the burner stay inside the boiler, the more that will get transferred to your water. Also the sizing of the firebox area is much smaller, concentrating the same heat to the boiler tubes at a much higher level than the early boilers - you don't need all that room for coal anymore. Well what we came up with was a self designed baffling system to obtain the same modern solutions. Firebricks were stacked in the corners supporting 1 inch square stock steel running across the front and back walls. Then two plates were made that sit above the firebox in the middle and lean against the outside "water wall" tubes - the initial and highest point of heat transfer in a boiler - basically creating a V shape. What this now does is re sized the firebox area to about 1/3 the original area, and forces the heat created against the sides of the boiler where the tubes are and then up to the secondary stages of the boiler. Also the small opening left for the heat to escape to the secondary stages slows down the draft. Will it work???? You'll see....

Baffle plates sitting above firebox

Finally the pipes feeding the radiators were cleaned and pained with Rustoleum, then the supply lines were insulated to also help with efficiency. It's a gravity system, without a circ pump. This is another modification that will need to be made, but not until after this season.


Patricia W said...

That thing turned out beautifully! Did you do all of this yourself? I wouldn't know where to begin.

My house has a 58 year old Sears Homart that is horribly rusty and very ugly but it works great.

I have thought about having it replaced but have read so many horror stories associated with new boilers that I don't want to let it go. I'd rather have it restored.

Are the pipes painted with gray paint?

mike & rachel said...

Yes that was all me, with some help from my dad who is a master welder/mechanic at a power plant with coal/oil/gas boilers 5 stories high! My buddy John also helped who worked on heaters in the early 70's before starting his own electrical business (who started me in electrical work). The only drawback with new boilers are many of the cheaper ones aren't cast iron anymore, which is very durable and like a stove holds heat for a long time even after the boiler is not firing. A good cast iron unit will run into the $10,000 range. Sizing is also a key problem if not done right. But there are many out there that really should be replaced and not much can be done to improve them. Remember the burner on my unit is not very old so the main concern is the efficiency of the boiler.

Yes the pipes are painted with grey Rustoleum. I then insulated the supply pipes, wasn't cost effective enough to do the returns.