Stop living in the confusing, one-dimensional realm of monocolor pressure hoses. You know, that world where there always seems to be a spaghettilike, tangled pile of clear pressure hoses at your feet as you surge through your building diagnostics; where you wander about, trying to trace the path of a particular hose so you can record the meaning of a specific reading on your pressure gauge; where you're always waving your hand to your coworkers; where you need to use smoke to establish pressure direction after you have used a manometer to measure pressure magnitude.

Now the manometer law and the standardized color hose code can be used with a wide range of everyday and esoteric pressure diagnostics. Their use makes it easy to identify pressure location quickly and fills every day with the cheer of holiday colors in the fast moving world of pressure measurements.

The manometer law was created by John Tooley of Natural Florida Retrofit, and color hoses were brought to our attention by Bruce McKendry of Watts Right, also in Florida. The law, the hose colors, and a whole family of training figures are standard fare in the two-week Duct Diagnostics and Repair Training program at the Alternative Energy Corporation (AEC), Applied Building Science Center.

Now connect a pressure hose to either or both manometer ports as dictated by the version of the law that you state. Our manometer has two channels--A and B--each of which has two pressure ports where hoses can be attached. The manometer always indicates the pressure at the high port with reference to the low one for each channel. With enough hose connected properly to the correct ports, you can measure any pressure from anywhere.

To enhance the law, use the four-color pressure hose code. Green is for outside pressure; red is for fan pressure (blower door or duct airtightness tester); blue is for duct pressure; yellow is for combustion draft pressure; and traditional clear is for any other pressure you want to measure.

Figure 1 illustrates the use of both the manometer law and the hose color code to determine the potential for pressure-related hazards in a combustion appliance zone with a natural-draft furnace. "Combustion Appliance Zone (CAZ) WRT Outside" is measured with clear and green hoses on channel A of the digital gauge. The -3.9 Pascals measurement shows that the CAZ is more negative than our standards allow. The second measurement, "Vent WRT CAZ," is taken with yellow and clear hoses on channel B, and yields +4.2 Pa. Using the manometer law, a positive pressure reading means that the air flow is from the zone measured by the high port to the one measured by the low port. In this case the +4.2 Pa measurement indicates that air is coming down the vent rather than that combustion byproducts are exiting up the vent.

Figure 1. The combustion appliance zone (CAZ) is tested for pressure-related hazards. (Note: the manometer does not actually show both measurements at the same time. You must switch between channels A and B.)	Figure 2.The ducts are depressurized to determine total leakage (including leakage to the inside of the house) from a duct system in a new house.

The hose color code is also extremely useful during blower door and duct leakage testing. Figure 2 shows the hoses used while depressurizing a duct system to test for total leakage. The crew capped off each supply register, attached a duct testing device to the return, and depressurized the ducts. Channel A measures the duct at a supply register (blue) WRT outside (green). When channel A shows that the ducts are depressurized to -25 Pa, the user switches to channel B to get the fan (red) pressure WRT location at the fan sensor (clear), which can then be converted to leakage.

While this test gives total leakage, many utility programs in our area are interested more in the duct leakage that's escaping to the outside, particularly for retrofitting existing construction. Figure 3 represents a test for duct leakage to the outside, using duct depressurization and a blower door simultaneously. The duct tester hookup is the same as in Figure 2. The blower door is used to depressurize the house at the same time in order to equalize the pressure between the house and the ducts (both are depressurized to -25 Pa). Since blower doors often come with a magnahelic gauge, this is used to measure the outside WRT house pressure, represented at the right of the diagram. (This is backwards from the manometer law, which would normally dictate reading house WRT outside, but the magnahelic gauge measures only positive pressures. Thus, the +25 Pascals we read on the magnahelic gauge indicates that the house is depressurized with respect to outside.)

Figure 3. Both a duct depressurization device and a blower door are used to determine leakage to the outside.

These are examples of common diagnostic procedures that benefit greatly from a standardized manometer law and color hose code. If you are setting up pressure hoses in a number of building pressure zones for training purposes or for long-term monitoring, you may want to use four additional hose colors: black for garage pressure, white for basement pressure, orange for attic pressure, and purple for crawlspace pressure.