Retrofitting an Existing Structure for Radiant Heat
Many people would like to replace or enhance an existing heating system with radiant floor heat. Good news! It can be done. Of course, the cost and difficulty varies considerably from project to project. In some cases, a do-it-yourselfer can manage it themselves. In other cases, a local radiant heat contractor might be necessary. In any case, it is critical that you start planning your project well in advance of the actual installation. As with any heating project, it is necessary to first understand the heat load requirements. This is typically expressed in BTU’s per hour and dictates the required heating capacity of the boiler or water heater (heat source). Some projects may already have a heat source on site. Knowing the BTU/hr output of the existing heat source versus the requirements of the space after it is modified will determine whether the heat source needs to be replaced or augmented. Even if the existing heat source has sufficient BTU output, its age and operating efficiency might suggest replacement for the lowest overall cost of ownership. Reusing an existing heat source may also complicate the plumbing for the new radiant system, versus a completely new system. The most significant hurdle in a retrofit project is installing the PEX tubing where finished ceilings and/or floor coverings may exist. Obviously, accomplishing the installation during a remodel where these areas might already be "open" is ideal. As with new construction, in a retrofit, PEX tubing can be installed over or under the sub-floor. Installing over the sub-floor can be a "non-starter" for many projects. Whether done via a lightweight concrete/gypcrete pour or lumber overlay the result raises the floor height by a couple of inches. In many, if not most, cases a raised floor just doesn’t work relative to counters and door jambs. Stapling PEX tubing under the sub-floor is generally the best solution for a retrofit. However, it does require access from below and hence a ceiling may have to be taken out and replaced. Accommodation will also have to be made for tubing in walls going from one floor to the next. In some situations, a mixture of in or under floor hydronic (water-based) radiant heat and other complementary heating types might be most practical. For example, baseboard radiators might be used on upper floors where installing tubing over or under floors is not practical. This approach allows you to have in or under floor radiant heat in, say, a basement and main floor, and radiators using the same heating source in the second floor and above. Electric in-floor heating systems can be used as a complement to hydronic radiant floor systems. While generally not feasible for whole house heating, electric cable or mat systems may have little or no impact on floor height and can be in used in small areas.