Quite often we go through a value-engineering process to save money on a project. Nowadays value engineering seems to take place even if the project comes in under budget and can be constructed within the constraints in the specifications.
Pipe insulation serves many purposes: reduction of heat loss, freeze protection and condensation protection.
One item that seems to come up almost every time is changing the pipe insulation from a fiberglass material to a closed cellular material. That, in and of itself may not be bad, but what seems to happen is that when we change the material, the thickness of the insulation seems to change too. For example, 1-in.-thick fiberglass turns into ´´-in.-thick closed cellular. There goes the insulating value.
We once had a project where I did not think about how significant the change could be when we agreed to alter the material. We allowed the material to be switched from fiberglass to a closed cellular type insulation on the domestic water piping. The hot water supply piping was not recirculated back to the water heater since we were using a heat-tracing hot water maintenance system. When the insulation was changed, the thickness dropped from 1-in. thick to 1/2-in. thick.
The particular product used did not fit exactly to the outside diameter of the pipe. This caused an air gap between the piping and the insulation, right where the heat tracing was applied. The effectiveness of the heat tracing was greatly reduced.
The heat that was supposed to be transferred to the water was instead transferred to the air space between the pipe and the insulation. To complicate matters further, the heat tracing was sized based on the thickness of the fiberglass insulation and not the reduced thickness of the closed cellular material. That meant the heat trace did not have enough heat input to keep the water warm in the pipe. Many people, myself included, became very unhappy when the hot water at the faucet could not be maintained at a comfortable level.
We eventually did get the system functioning but we had to add another layer of insulation to the piping and change the voltage of the heat trace to allow it to conduct more heat. That was an expensive “value-engineering” experience.
I don’t want to convey the notion that closed cellular products do not provide adequate insulation properties. They do. But I would like to point out some factors that you should think about when looking at insulation and how it is applied.
Pipe insulation serves many purposes: Reduction of heat loss, freeze protection and condensation protection as well as just being there to protect you from touching a pipe that’s too hot. The purpose of the insulation determines what type of insulation you may want to select.
Heat tracing can also be a factor in the selection of insulation. You should verify product tolerances with both the insulation and heat-trace manufacturers before installation. Then find out whether the heat tracing and insulation will work together.
While basic thermal conductivity is slightly different for both types of insulation, fiberglass and closed cellular fall into the minimum limits set forth in ashrae 90.1-1989 for heat loss. Ashrae 90.1 requires pipe insulation to be 1-in. thick for pipe sizes 2 in. and less, and 11/2-in. thick for pipe sizes 21/2 in. and larger. There is also an allowance for 1/2-in.-thick insulation on small runouts (less than 2 in.) that are not longer than 12 ft.
These insulation thicknesses are applicable to domestic hot water piping systems. If you’re using the insulation on other systems, you should consult the local code as well as the insulation manufacturers’ literature for other required thicknesses. Insulation should be provided on all piping, especially on commercial projects but also on residential jobs. Limiting the amount of heat loss in piping systems can have a major effect on the amount of energy used to heat water and the amount of water that is wasted waiting for hot water to be delivered to the faucet.
Do not forget to insulate cold water piping in domestic water systems, especially when you are installing the piping in colder climates. Condensation that forms on the outside of the cold water piping can damage many of the finishes in a building and leaves unsightly stains on ceiling tile and other surfaces. Consult the manufacturer’s literature to determine how much insulation should be used to prevent condensation.
Storm water piping is also susceptible to condensation and should be insulated from the roof drain bowl to a point where the piping turns from horizontal to vertical. In any event, the storm water piping should be insulated for a minimum of 30 ft. from the roof drain. Once again, condensation can damage building finishes and nothing is worse than water stains from tar-coated cast-iron piping.
As one of my favorite sayings goes, think about what you’re doing. If you are considering changing the pipe insulation on a project, be sure you are not causing more harm and spending more money in the long run.
Joe Scott is an associate and chief plumbing engineer with Phillips Swager Associates in Peoria, Ill., tel. 309/688-9511, e-mail [email protected]