Sidearm Heat Exchanger

[Eric Johnson]

As part of my ongoing boiler upgrade, I decided to make a bigger sidearm heat exchanger for getting heat from the heating system into the water heater. This one uses a 1.5-inch shell with a 1" boiler water inlet and outlet. The tube (domestic hot water) going down the middle is 3/4-inch copper. When you pump 160+ degree water through the shell from top to bottom, it causes the domestic water in the 3/4-inch tube to convect by gravity, heating up a 50-gallon hot water heater surprisingly fast. We've found that as long as we keep the boiler going, we never run out of hot water.

I cobbled this together mostly from parts I had on-hand, which explains the coupling and series of reducers. If you were going to make one from scratch, you could get by with fewer, more specialized parts. I thought it was a good idea to pressure test the whole thing before installing it, since it took a fair amount of soldering and I was re-using most of the parts. Good thing, too, because it had two leaks that were relatively easy to fix as is, but would have been a nightmare once the thing is hooked up.

 

[Eric Johnson]

Here's an old diagram I made attempting to show how a sidearm heat exchanger like this works.

 

[Eric Johnson]

Compare that to a flat plate heat exchanger. This one is rated for 150,000 btu/hour (max). It's what I'm going to use to charge up the 1,000-gallon storage tank.

 

[carpniels]

HI Eric,

Good to see you are upgrading the water systems. Sorry that copper is so expensive now. But then again, you seem to be reusing a lot of the parts.

I am sure this is all prep work for when the new boiler is supposed to arrive. Good thinking. Nothing worse that a perfect boiler and no or only a limited way of getting the heat it produces to the house.

Keep us informed on your progress and when you need me to show up for installation.

Thanks

Niels

 

[BrotherBart]

Compare that to a flat plate heat exchanger. This one is rated for 150,000 btu/hour (max). It's what I'm going to use to charge up the 1,000-gallon storage tank.

Is that a meat thermometer?

 

[Eric Johnson]

Of course. They're the perfect temp range and like me, they're cheap. I've got 'em all over my system.

Niels: I have most of the copper already installed. I have to put in about 150 feet of pex, but other than repiping to accommodate the hot water storage tank, everything is pretty much in place. If this hot weather keeps up, I'll be wrapping 'er up pretty quick, since I'd rather spend hot days in the basement than outside.

My goal has always been to have everything ready to go before getting the boiler. Got all the new pumps, aquastats and some copper fittings on Ebay. Getting the boiler prepped and moved into place will take long enough. So I'm still shooting for late July/early August.

 

[BrotherBart]

You betcha. Hey, I am the guy with the Char-Broil eight buck bbq probes in the stacks on the stoves.

 

[Eric Johnson]

Hey BB, where do you think I get my inspiration?

I have to run up to Canada on business for the rest of the week, but when I get back I'm going to get this thing hooked up to the water heater, and then start working backward from there to the tank. That will involve connecting to the gas boiler, so there's a fair amount of black iron work involved as well. Time to start swinging the big wrenches.

I'll post pics in case anyone is interested. One more incentive to do a nice, neat job.

 

[Eric Johnson]

I got a lot done over the 4th of July weekend. I started at the water heater, which is where the wood-side of this heating system basically terminates. Anyway, I got the sidearm hooked up to the heater, then piped into the gas-fired boiler. The piping on the gas boiler is mostly black iron, which was cheaper and fun to work with, and designed so that I can 1.) bypass the gas boiler; 2.) bypass the hot water heater; 3.) flow through both. It's just a matter of putting some valves in the right places and connecting everything up right.

Surprisingly, everything pressured up with no leaks.

Currently, I'm a bit downstream, (to the left) putting in the heat exchanger for the tank, along with a couple of pumps, a three way zone valve, etc.

 

[Eric Johnson]

Here's where the 1" supply line connects to the gas-fired boiler, and a blurry view of the completed piping arrangement.

 

[Eric Johnson]

The inlet on the gas boiler is a 1" tap that had a 3/4-inch reducer and pressure relief valve. Came right out with a little wintergreen oil and elbow grease.

Also, here's the piping scheme.

 

[slowzuki]

Looking good Eric!
Ken

 

[BrotherBart]

Compare that to a flat plate heat exchanger. This one is rated for 150,000 btu/hour (max). It's what I'm going to use to charge up the 1,000-gallon storage tank.

The day that big tank comes up to temp the first time a person wouldn't be able to wipe the grin off of your face with a splitting maul.

At Big Oil headquarters they had a similar rig. Seems that most of the building heat during the day was provided by body heat and they supplemented that with solar to charge up a 10,000 underground tank that they heated the place with at night. On my building tour I commented that here I thought they transferred me because of my potential only to find out all they wanted was my body heat.

Da new setup be lookin good guy. When is that honkin boiler due?

 

[Eric Johnson]

Takes about a week from the time you order it, so whenever I decide to pull the trigger.....

I'll probably spend a couple more weeks emailing the guy for the exact dimensions, fretting, sweating, etc. before I get fed up being nervous and just order the damn thing. There ain't much room in my boiler room (we're talking inches) and I don't want it to arrive and not fit. If there was any piping coming out the front or either side, then it wouldn't fit. But I do have some wiggle room top and back, so it should be OK. I hope.

The manual and specs are translated from metric/Polish, so I want to make sure some important dimension didn't get garbled in the process. Maybe have the guy go out and actually put the tape to one just for peace of mind.

The shipping is cheaper if you have it delivered to a commercial address with a forklift. Since I have a tractor and farm implement dealer about two blocks away, I know I can pay them to receive and deliver it. I'd rather just rent one of their forklifts and unload it right here at home (got other uses for a forklift), but then it's not a commercial address, and the price goes up. So I've gotta work that out with the tractor guys.

I hope the tank-induced grin isn't like one of those bad blue pill reactions you hear about on TV: "See your physician if it lasts longer than 4 hours." Had one in high school that lasted for about 4 years. A grin, that is.

 

[BrotherBart]

My wife says that at four hours I would be calling everybody I know to tell them about it. Probably post it on hearth.com.

 

[Eric Johnson]

I made the guy go out and put a tape to one. The boiler is 31.5 inches wide. My cinder block boiler room is 34, so I've got plenty of room to spare. Silly me!

And the tractor implement place said no problemo taking it off the truck and driving it up to my house. No charge, either. That means a nice tip for the forklift operator.

 

[slowzuki]

That my friend is pretty darned tight, how do you get to all the connections?

 

[Eric Johnson]

Actually, the boiler is 29 inches wide. There's a heat exchanger cleaner lever mounted on the left side that uses up an additional 2.5 inches.

All the connections are either on the top or the back, where I have considerably more room. Probably still use more street fittings than I'd like. My plan is to park the thing in the garage to get all the piping in place (black iron, for the most part), pumps mounted, etc. and then wheel it into the boiler room with a pallet jack, and connect the lines and wiring. The boiler room has a door in the front and one in the back, so there's access to both ends. Here's a pic from a few years ago of the room under construction with my current boiler in place. That's gotta come out of there pretty quick.

 

[mmmvlm]

I have a question about sidearm does the water from the boiler have to be pumped or can it be gravity fed

 

[Eric Johnson]

Hi mmmvlm. Welcome to the Boiler Room.

Typically, you pump boiler water through the outside shell of the sidearm. The water domestic hot water circulates through gravity. However, with the right setup, I don't see why you couldn't make gravity work on both sides. But you'd have to design it right.

 

[mmmvlm]

At this stage of the game I guess pumping is the way to go then. I take it a Taco 007 would work well and just let it run.

thank you this is the best site on the web, love it

 

[Eric Johnson]

If you want to get fancy, wire the circulator through the theromostat on the hot water heater. When it drops below the setpoint, the pump kicks on. And yes, a 007 should work fine.

Or, you could set it up so that water bound for your zone(s) always goes through the sidearm, either on the supply or the return. That saves the expense of a dedicated pump, unless the rest of the system is on gravity, in which case you need one.

BTW, I thought you had a coil in your boiler. If that's the case, you don't need a sidearm heat exchanger. Same basic principle though, when it comes to heating up water in a hot water heater, as I described in my email. The main difference is that with a coil in the boiler, you need to pump the fresh water side through the coil. Ideally, you should use a bronze circulator to avoid corrosion. But since they cost like hell, I've had luck using a cast iron circulator and replacing it every couple of years. Actually, I used one for about five years and never had a problem. Nofossil and Joe Brown will probably slam me for even suggesting such a thing, but what can I say? It worked for me.

 

[BrownianHeatingTech]

A 007 would be more than enough, if the boiler is near the sidearm. Sidearms have very low flow resistance... a 005 or even a 006 would be fine. (yes, that's worded correctly - a 005 flows more than a 006 - Taco's numbering is not sequential with performance)

As far as gravity flow, you might need to raise the tank to get the flow going enough, depending on your application.

Joe

 

[Nofossil]

So.... does the sidearm exchanger try to heat the boiler with the hot water tank via thermosiphon when the boiler is cold?

 

[BrownianHeatingTech]

So.... does the sidearm exchanger try to heat the boiler with the hot water tank via thermosiphon when the boiler is cold?

Depends on the piping. In most cases, a check valve is used on the boiler side, it prevent that. The force it takes to open the check valve, while small, is greater than the thermosiphon can generate.

Joe