1. Applying radiant in non-hydronic applications
Add-On Radiant
This program discusses how to add radiant heat to existing non-hydronic heating systems, specifically forced air and steam systems. It can be done, and quite easily, if you take advantage of the products that are available.
Applying radiant in non-hydronic applications

2. Challenges Radiant with existing forced air?
Radiant with existing steam?
Non-barrier tube with ferrous components
NO WAY!
Radiant floor heating in new construction is fairly straight-forward. It’s tubing, controls and heating plant. There aren’t too many hoops to jump through. Adding radiant to an existing structure that already has hydronic heating is a little harder, but not much. You simply need to tap into the existing boiler, add your controls and tubing and presto, radiant heat. But what if the house doesn’t have hydronic heat already? Does that mean the challenges outweigh the opportunity? Well, first let’s review the challenges?
What about radiant with forced air? Since the tubing needs warm water and not scorched air running through it, it would seem unlikely that we could add radiant to that system. We would need to provide a completely separate and dedicated heating source to the job. Ditto with an existing steam system. PEX tubing doesn’t do well with steam, so another heating source would need to be provided.
Often, a homeowner or installer may try to simply run some tubing in between the floor joists and then connect it directly to their existing water heater in what would be considered an “open” system. While this type of a system would “work,” unless the installer understands oxygen diffusion there is a substantial risk that the system may combine non-barrier PEX tubing with ferrous components – usually the circulator, expansion tank and air separator. This can lead to considerable corrosion issues for all the ferrous components in the system. In addition, an open system may violate local mechanical codes and could endanger the end user by allowing domestic water to lay stagnant in the radiant tubing all summer long.
With all these inherent challenges, the prevailing attitude toward adding radiant floor heating to existing homes that don’t already have hydronic heat is – “no way.”

3. Challenges = Opportunities
Well, not so fast. The flip side of a challenge is an opportunity. We can add radiant to existing forced air systems and existing steam systems without worrying about oxygen diffusion corrosion or potentially dangerous open systems. We simply need to use the right approach.

4. Taco X-Pump Block Talk about unique! Heat exchanger
Injection circulator
System circulator
Outdoor reset control
How can we do all this? The Taco X-Pump Block. The X-Pump Block is one of the most unique products in our industry. It combines a flat plate heat exchanger with two circulators – one for injection into the heat exchanger—the other for the radiant system, along with an variable speed injection mixing outdoor reset control in one simple, compact, easy to wire unit.

5. Some Cool Stuff… Only 4 pipe connections Speedy installation
Saves time AND space
All bronze casings
Easy, plug in wiring
Manifold ready
Handles loads up to 50,000 BTUH
The Taco X-Pump Block is an all-in-one package that makes adding radiant to non-hydronic heating systems easy. The piping arrangement is dead-simple, requiring only four pipe connections. This makes for a speedy installation that not only saves the contractor time and money, but it also saves precious space in the mechanical room. The all-bronze casing means the system can be connected directly to an existing water heater on the heating plant side of the heat exchanger, and directly to non-barrier tubing on the radiant side of the heat exchanger. You will, of course, need to make sure you use all non-ferrous piping and accessories on the radiant side – specifically an all bronze air separator as well as a potable water type expansion tank.
The wiring is also simple – low voltage zone and sensor wiring to the outdoor reset control and a simple line voltage plug to power up the unit. In addition, the radiant heating side’s supply and return tappings are designed to connect directly to most any packaged radiant manifold available – the supply and return tappings line up with the supply and return of any radiant manifold, with the appropriate offset built in.
While output ranges vary based on BTU’s available and incoming supply water temperatures at the heat exchanger, the X-pump block can handle up to 50,000 BTU’s worth of heating, making it a workhorse that can handle anything from a simple bathroom floor warming job up to a small addition.

6. Flat plate heat exchanger
X-Pump Block Anatomy
Radiant Return
Radiant Supply
Injection Circulator
Radiant Circulator
Flat plate heat exchanger
Heating plant supply
Heating plant return
Power cord
Mounting Brackets
Reset control
Here’s what the X-Pump block looks like from the outside – note the integral flat plate heat exchanger on the back – built in to separate the heating plant water from the radiant system water. Also note the integral mounting brackets designed to make installing the X-Pump block very simple and fast.

7. Basic Piping Arrangement
Here’s your basic piping arrangement for the X-pump block. On the left hand side you see the heating source supply and return heading into and out of the integral flat plate heat exchanger. On the right hand side you see the supply and return for the radiant heating system, with the supply on the bottom and the return at the top. You’ll also note on the right hand side an expansion tank – one is required because the heating side is a closed loop system. You’ll also see an air separator and a 30 pound pressure relief valve, to protect the closed loop system.

8. On The Inside…
Here’s a cutaway of the X-block’s all bronze casting. The heating system water enters the X-Block through port A1. The variable speed injection circulator at the top of the block moves water through the heat exchanger, returning it to the heating plant through port A2. The radiant system water enters the block through port B1. A fixed speed circulator moves the system water through the other side of the heat exchanger and then back to the system through port B2. The two waters are separated by the heat exchanger, while the temperature of the radiant system water is controlled by the X-Block’s outdoor reset control. The variable speed circulator on the heating plan side will go faster or slower to control the water temperature on the radiant side.

9. Using Existing Water Heater
Here’s a piping arrangement for the X-Pump Block connected to the domestic water heater. You would use this application if the home already had forced hot air and didn’t have any other hydronic source for radiant. The heating plant side of the heat exchanger would be supplied off the hot water line coming out of the water heater. Make sure to use a check valve on the inlet to prevent any possible cold water flow back into the hot when the block is not in use. You can also see the return from the X-block is connected to the cold water supply. The hot water side also has a tempering valve installed – this is used in the instances when the tank temperature may need to be increased to handle the radiant heating load. In that case, if the tank temperature is too high and could lead to scalding, the tempering valve is needed to control the domestic water temperature.
On the radiant heating side of the X-pump block, you see the supply to the radiant manifold coming out of the bottom of the block, with the return on the top. You also see the air separator and expansion tank on the return side. If you use non-barrier tubing on the radiant system, it’s critical that both of these components be non-ferrous to prevent oxygen diffusion corrosion. If you use barrier tubing on the heating side of the heat exchanger, then both can be standard hydronic components. Also note that a 30 pound relief valve must also be installed. This is a closed loop hydronic system, and needs to be protected.

10. 3350 Pressure Reducing Valve
Boiler/Injection
Circulator
3350 Pressure Reducing Valve
Boiler Return
4900 Air Separator
Expansion Tank
The X-pump block can also be used on an existing steam boiler, providing hot water for the radiant system by circulator below the condensate line. You see the supply coming off the bottom tapping, with the return coming into a higher tapping. Since the steam boiler is an open system, you’ll need to supply from the lowest point to help keep the net positive suction head on the inlet side of the injection circulator as high as possible. All circulators need a minimum amount of pressure on the inlet side, or else they can actually flash to steam inside and cause cavitation, which will shorten the circulator’s life. So not only should you take the supply tapping off the boiler’s lowest point, the X-Block itself should be mounted as low to the floor as possible. Another option would be to install a second circulator on the supply pie leading into the X-block, but it’s easier and less costly to simply mount the X-block as low as possible.
Also note the Wye strainer on the supply piping heading into the X-Block. The water in a steam boiler is bound to be very dirty and filled with cruddy deposits. The strainer is needed to keep the water as clean as possible going into the heat exchanger. The water path through the exchanger is very narrow, and even a small amount of junk can cause flow problems and possibly even plug up the heat exchanger.
On the radiant heating side, the installation remains the same, with the supply coming off the bottom of the block, and the return on the top. Also note the air separator, expansion tank, relief valve and pressure reducing-cold water fill valve.
Boiler Supply
Radiant Manifold
Wye Strainer
Radiant Circulator
30# Relief Valve

11. How many BTU’s can the X-pump block handle
How many BTU’s can the X-pump block handle? Here’s the sizing chart for radiant systems using a 20 degree delta T. As you can see, the relative output depends on the incoming water temperature from the heat source, as well as the required water temperature in the radiant system.
Let’s to an example. Let’s say we’re doing a water heater job. The water coming from the water heater is 120 degrees. If our radiant system is a kitchen floor warming application that needs 110 degree water, then the X-block will be able to provide about 4,500 BTU’s. In a kitchen with about 400 square feet of open floor space – not included cabinets – that would equal about 15 BTU’s per square foot, which should be able to keep the floor at about 72 degrees on the coldest day of the year, if the floor was tile or vinyl.
If, however, we were using the condensate off the bottom of a steam boiler, we would assume that supply water to be about 180 degrees. In the same scenario using 110 degree supply water for the radiant, we could produce almost 60, 000 BTU’s total, and keep producing that amount of heat until the required radiant supply water exceeds 150 degrees.

13. Easy Programming View screen & programming buttons
Menu (View & Adjust)
Item
Up & Down programming keys
Programming the X-Pump Block, and understanding its operation, is very easy if you can keep some simple terminology in mind. All programming is done using the LCD View Screen and the programming buttons, shown here. The first button is the Menu button – this allows the user to scroll between the different programming and operation menus. There are two with the XPB – the View Menu – which tells us what the XPB is currently doing, and the Adjust Menu, which is used for programming. Once we select a menu, the Item button allows us to scroll through different Items within each menu, as we will see in a moment. The up and down arrow keys are used in the Adjust Menu only, and are used to setting programming values.

14. The Adjust Menu Quick & easy setup Outdoor design temp Mix Design temp
Mix Max temp
Mix Min temp
Min Boiler Return temp
WWSD
Units
To program the control, use the Adjust Menu. Setup for standard operation is very quick and easy, provided you understand the terminology. First, press the Menu button until the word Adjust appears in the upper left hand portion of the screen. You are now in the Adjust menu. The first item in the adjust menu is outdoor design temperature, or the temperature upon which your heat loss was based – the so-called “coldest day of the year.” In this example, we’ve set the outdoor design temperature to 10 degrees. (note – if the outdoor design temperature setting is set to “OFF,” then the XPB will work in Set point mode and maintain a fixed water temperature for the radiant system).
The next item is the Mix design temperature, or the temperature you want the RMB to produce when it’s 10 degrees outside. Your radiant design calculations will tell you this number. In this example, the Mix Design Temperature is 120 degrees. Hit the button again and we get to the Mix Max temperature setting – this allows us to set a maximum water temperature for the radiant system in case the outdoor temperature drops well below the design setting. We may do this to protect hardwood floors, for instance, or to stay within design guidelines. Typically, this will be set at either 150 degrees – which is the maximum for all concrete applications (could be as low as 145 for gypsum, depending on the manufacturer’s guidelines), or 165 to 170 for between the joist applications – again depending on the manufacturer’s guidelines.
Next is the Mix Min temperature – or a setting for the minimum radiant system water temperature. In this example, it’s set to OFF, meaning the water temperature will go as low as the reset curve will allow. Typically, however, this may be set anywhere from 70 to 90, depending on the type of installation. Next is WWSD, or warm weather shutdown. This is a function that will turn off the heating system at a certain outdoor temperature. Typically this is set to whatever temperature was used as an indoor setpoint when conducting the heat loss, usually 70 degrees. So when the outdoor temperature reaches 70 degrees – which matches the desired indoor temperature, the heat loss of the building should be zero, and therefore the heating system can be shut off. Often, this is set a tad lower than perhaps as low as 65 or 60 – since most folks don’t turn on the heat at those temperatures.
And the last item is units – either Fahrenheit or Centigrade.