If you are a contractor like myself, you are always looking for ways to get an edge on boiler installs. We all want to end up with a happy customer and a decent profit from the job. A happy customer and a decent profit go hand in hand; however, they require some ingenuity on the contractor’s end. 

Let’s say Harry the homeowner needs a new boiler. He calls several reputable companies to come in and bid the job. You happen to be one of them. After all the interviews are conducted and the bids are in, he chooses you to do the job. 

He may not tell you why but the ball is in your court now. The price is set and you have to deliver. You want Harry to be not just OK with your work; you want him to be ecstatic. You want him to look at the completed job and say, “It was well worth the money.” Because if he is pleased, getting paid for the job won’t be a problem. Plus, he is going to tell all his friends which is good for business.

How do we get Harry to that level of satisfaction?

By giving him more than he was expecting. First and foremost, we have to make sure the system we install is functional and safe. But that is what everyone does, right? Take it a step further and give him a system nicer than any he’s seen before. Give him a system that looks like a magazine photo. You will please Harry as well as your future customers. 

“Yeah, but it all sounds expensive and the price is set,” you say. “Where is the part where we make a decent profit?”

I replay, “Efficiency!”

“Whadda ya mean? Me and my guys work hard and fast. We get the job done and there is no fooling around.”

All contractors are sensitive about this sort of thing. 

“How many times do you run to the supply house for a fitting or component while you are on the job?” I ask.

“I dunno, maybe half a dozen times,” you say. “But you know as well as I do, boiler jobs take all sorts of fittings and a lot of them. There is just no way not to miss a few parts when getting a job together.” 

“What if I said you could have those six hours of labor back in your pocket? Time wasted running to the supply house is time you don’t get paid for. No work is getting done. And it’s eating into the time for your next job.”

“Yeah, but … ”

“With prefabrication, you can do most of the install work in your shop. Take a piece of plywood and mount the wall-hung boiler, all the controls and the near-boiler piping. Then take the whole thing out to the jobsite and screw it to the wall. All that’s left is to connect the piping and the wiring.”

“It will save me that much time?”

Think about it. You are working in your shop. You have all your supplies and tools at arm’s reach. You have your bins of fittings and racks of pipe. You won’t need to make those runs to the supply house. Everything is right in front of you. 

And think about all those bins of fittings and the tools you carry into basements and then back out to your truck. Prefabbing will save you from a lot of those basement trips. Depending on the jobsite, this can be a huge gain in efficiency. Save your knees and legs for when you are older. 

I would be remiss not to mention that prefabbing is mostly benchwork. I think we all get a little bit giddy when we get the opportunity to do bench work! In my area, we call it “gravy work.” In this setting, one person can do the work of two in less time. That is efficiency.

Tips and tricks

Contractors who prefab have their own way of doing it. No doubt you will as well. I would like to share some tips and tricks that I use; perhaps you will find some of them useful.

Start off with a piece of plywood. That much is pretty obvious. But which one to choose? Many different possibilities are available at several price points. I like using furniture-grade 3/4-inch plywood. It stays nice and flat, where sheathing-grade plywood will warp if there is rain in the forecast on installation day. The furniture-grade plywood also has a nice veneer on it, such as maple, birch or oak. A birch veneer is my first choice, with maple being a close second. 

The reason the veneer is important to me is that it improves the consistency and texture for my finished, painted surface. Everyone has a preference when it comes to paint colors and finishes. Mine happens to be flat black. I think it makes the copper piping and hydronic components pop. The matte texture also hides a multitude of sins pertaining to ones’ painting skills. 

 

The next thing to consider is how to fasten everything to the plywood. Do I use 3/4-inch screws? It doesn’t sound very strong, especially when you are talking about a 150 lb. boiler. I found the answer at my local Lowes. Tee nuts! Drill a hole in the plywood and insert the tee nut from the back. Now you can bolt your boiler wall bracket and strut securely.

Don’t forget to use unions in the piping that connects to the boiler. The prefabbed board is much easier to carry down into the basement with the boiler removed.

Wiring is something that can easily mess up the looks of an otherwise attractive boiler job. Try using electrical metallic tubing (EMT). It cleans things up and you can run multiple conductors in one pipe. The switch cuts power to the whole system: the boiler and the zone control. The conduit then comes out of the bottom of the switch box and to a junction box right below the boiler. 

All the metal-clad cable from the pumps come into this junction box as well. Here all the neutrals and grounds are connected. Then a single conduit is installed from the junction box to the boiler. This conduit carries the 120V power supply for the boiler, equipment ground and three conductors for the pump outputs. Finally, a receptacle is installed in the box to power the condensate pump. 

Designing the prefab panel is perhaps the trickiest part of the process – getting all the components and piping on the board in an organized manner. The piping must be hydronically correct and all the hydronic components must be installed in such a manner that they can easily be isolated and serviced. (Tip: Zone valves take much less space than pumps for zoning.)

You have a blank board in front of you. Where to start? 

I usually unpack everything first. Find a suitable spot on the board for your wall-hung boiler. Heed the recommended clearances in the boiler manual and make sure you position it so the venting will work once you have your prefabbed panel installed on-site. Install the flanges on the pumps finger-tight. Lay out all your components on the board. You have to have an imagination for this part. Shuffle them around until you are satisfied that everything fits perfectly and works with your piping schematic. 

Make sure to leave room between your components and pipe fittings for strut clamps. Try to arrange the piping to use the least amount of strut. It keeps the clutter down and saves time. 

Don’t start your piping until you have a clear picture of how everything will work and look. Then get it knocked out. You’ll be amazed at how fast this process becomes with a bit of practice.

Thermal migration

Most prefabs use a vertical piping arrangement. It’s about the only way to get everything on one piece of plywood. There is nothing wrong with this approach but, in some cases, it can cause problems. Just like a perennial, the problem of warm baseboards in the summertime and the quest for a solution comes up again and again. 

While there are a few different causes for this, a common one is thermal migration. 

It and gravity flow can occur in a pipe even when the other end of it is closed off with a zone valve. Let’s say you have a constant source of hot water at the bottom of a vertical pipe. The heat will conduct through the water until there is enough heated water at the bottom of the pipe to start gravity flow. 

The hottest water will begin to rise through the center of the pipe while the cooler water will drop down around the outside. Once the pipe turns horizontal or slopes up slightly, the hottest water will travel along the top of the pipe while the cooler water returns along the bottom. 

This phenomenon has plagued many homeowners with heat that was unappreciated and caused consternation among contractors who were tasked to solve the problem. 

Why not solve the problem before it happens? In this system, we have three baseboard zones and an indirect water heater. The system is piped primary-secondary.

In this case, the DHW return pipe could have become the source of heat for the central heating return pipe. Both have to connect to the boiler loop at some point. Now, only a portion of the boiler loop has water flowing through it when there is a call for DHW. However, but if the DHW return and the CH return connections are made at the wrong spot, the DHW return will introduce heat to the bottom of the vertical CH return. 

Use nature to solve the problem. It is much less expensive than check valves and it will work forever. In Picture D, the piece of pipe labeled “Thermal Trap” prevents thermal migration and gravity flow into the CH return. It is part of the boiler loop and has no flow while the DHW pump is running. 

Boiler Setup

When it comes time to set up the boiler, most of your tools are packed up. The materials are back in the truck and the floor is swept clean. You are perhaps in a hurry to get the system running and get to the next job. 

But don’t be in such a hurry. This is where you can do the homeowner a tremendous favor by ensuring the system runs at peak efficiency. To do this, you must perform two important procedures:  

1. Do a combustion analysis and ensure you have safe and efficient combustion.

2. Set up the outdoor reset curve properly. Contractors neglect this step more often than not. The house may have hot-water baseboard or radiators, but it does not mean it needs 180-degree water. 

The house I installed this system in has wall-to-wall baseboard. Every linear inch of exterior wall has baseboard installed. Although it was a colossal waste of money at the time, it’s perfect for the condensing boiler the homeowner now has. All the extra baseboard allows for a lower water temperature for design-day (coldest day of the year) conditions. 

But how do we figure out what that water temperature is?

One way would be to measure all the baseboard, then use a chart from the baseboard manufacturer showing the baseboard output at different water temperatures. Match the baseboard output to the heat load calculation of the house and use the corresponding water temperature to set the max design end of your outdoor reset (ODR) curve.

A quicker way is possible if the boiler allows you to control the fan speed for combustion testing. Take the heat load of the house and divide it by the net output of the boiler. You will end up with a percentage. Manually control the fan speed of the boiler and set it to that percentage. Make sure the pumps are running and the zone valves are open. Wait until the supply and return water temperatures have stabilized. Use the resulting supply water temperature to set the max design temp for the ODR curve. Make sure the house is at or very close to the desired temperature while you perform this test. 

The bottom end of the ODR curve is a bit trickier to set accurately. Most heating elements don’t have ratings at those cooler water temps. I hesitate to set standard baseboard at lower than 100 degrees because their heat output drops off so sharply at lower water temps. 

By thinking outside the box a bit, you can have the best of both worlds – a well-satisfied customer and a decent profit in your pocket