Electronic Tape Measures
I visited several big-box stores and my local hardware store to collect information for this article on electronic tape measures. The dust on top of some of the packages was pretty thick, and there was a distinct lack of customer support information from the sales staff. Do the manufacturers know something the retail world doesn’t? To help answer that question, I did a quick survey of people in the energy auditor business. I was surprised to learn that only about half of the auditors I surveyed used electronic measuring tools. I think the technology may be ahead of the market. If you are going to invest in one of these devices, it is important to know how you intend to use the tool before you buy it.
Electronic measuring tools use one of two technologies to measure distances: ultrasonic pulses or laser pulses. The ultrasonic units in general measure accurately only up to 50 feet, while the high-end laser units measure accurately up to 650 feet. (Some of the ultrasonic devices confuse the issue by providing a laser pointer to guide the user.) The ultrasonic units are less expensive; I couldn’t find an ultrasonic unit that cost more than $100. On the other hand, there are only a few laser measuring tools available for less than $100, although, with all the competition, the pricing is coming down.
The tools using the ultrasonic technology send out an acoustic pulse like a “click” and measure the time it takes for the sound to bounce back from the surface you are measuring. The device calculates the distance using the speed of sound travelling through air. Since sound travels at different speeds through air at different temperatures and humidity, the devices are not as accurate as laser tools. The ultrasound devices can be useful for simple do-it-yourself projects, such as determining the number of gallons of paint or rolls of wallpaper you need to paint or paper a wall.
Laser measuring technology uses laser pulses rather than sound to measure the distance between the device and a surface. Because laser devices are measuring distances at the speed of light, the process is fast and accurate.
When I started doing energy audits a long time ago, measuring the house and the windows and the doors and making a sketch while standing out in the rain was tedious and a pain. The process improved when I had a computer to do the calculations, but I still had to measure everything. With these electronic measuring tools, it can be simpler and quicker for a person working alone to get the job done.
Important Features to Look For
Walls, windows, doors, and floors all need to be measured to calculate the exterior surface area of the house to determine the performance of the thermal envelope. The attic area needs to be measured to calculate the amount of insulation to install. The volume of the house needs to be measured for ventilation calculations. The volume of the combustion zone needs to be calculated to determine if there is adequate combustion air. (Remember: 50ft3/1,000 Btu.) For an energy auditor, the accuracy of these numbers has to be reasonable, but getting down to ¹/³² inch isn’t necessary. Few houses are more than 130 feet in any one direction, so the range needn’t be longer than that. The product has to be durable to take the abuse that tools experience on a jobsite, and the batteries have to be easy to replace. Table 1 lists the important and optional features to look for.
For professional energy analysis work, I wouldn’t recommend an ultrasonic measuring tool. These tools aren’t really accurate enough to do the job, and there are many excellent laser-based tools.
The DLR130K is the least expensive laser tool on this list, and it is about as good as it gets for a basic tool. It’s only 4 inches tall. It’s tough, with a rating of IP54. It uses four AAA batteries. It’s simple to use with a minimum of buttons to push, but it still calculates area and volume. Like a basic calculator, it has a memory that can be added to or subtracted from. The memory is smart enough not to try to add an area calculation to a basic, single-point measurement value.
The Bosch GLM80 has all the necessary basic features. It is tough enough (rated IP54). It uses two AAA batteries. It does area, volume, and Pythagoras calculations. The GLM80 has a recallable 20-value data storage memory, but you will still need to write the information down so that you know what each measurement represents. It’s great to have a measurement, but if you don’t know what it refers to, it’s not going to be useful. The Bosch GLM80 has the minimum number of buttons, and its use is intuitive. The backlighting is automatic and is based on ambient light; this might be annoying, since it can time out at inopportune times. Many of the significant energy-auditing measurements, however, are done in bright, exterior light.
The 419D has a durability rating of IP54. It has nine buttons, including the Measure button. There are Plus and Minus buttons for taking a series of measurements. There is a button for the Pythagoras function for calculating a right-angle measurement. There is a button for making area and volume calculations. There is a Timer button that you can use to sweep over a point if you can’t see the exact spot. There is a Memory button and a Power Off/Clear button and a button for shifting the measure point from the bottom to the top of the unit. One of the things I dislike about all of these devices is the location of the primary measurement button. I wish someone would design a device with the Measure button on the bottom or on the side. The button on the top in the middle is fine if you can hold the device in your hand and point. But if you’re holding it sideways or over your head or in the dark, it is sometimes difficult to find the button. But they’re all like that.
The Hilti PD5 is shaped like a pen, so you can slip it into your pocket. The one-button On/Off switch doesn’t provide a lot of extra features, but it makes measuring simple. The present and most recent past measurements are displayed on the screen with a backlit display to make it easy to read in dark places. It uses two AAA batteries and has an IP55 rating. The display will be upside-down when shooting from left to right.
The DT300 has ten buttons on the face of it to address all of the functions, but they are clearly marked. The three-line display is backlit to make reading in dim places workable. It requires two AAA batteries. The instructions warn about using the device outside, on roads, or near construction sites without safeguards. With an IP54 rating, that’s sort of surprising. I didn’t get my hands on one of these to challenge it outdoors. It can recall 20 measurements; calculate area, volume, and Pythagoras functions; and add up a series of measurements.
Leica DISTO D8
And then there is the Leica DISTO D8. This device does it all—area, volume, and angles. It automatically adjusts the measuring point when you flip out the clip on the end of the unit. It automatically adjusts the illumination level with a light sensor. It has a Bluetooth function for communicating with your tablet or computer through an Excel spreadsheet on which you can move the cursor around with the D8 keys. One of the best features is a video capability, so that you can see the laser dot with a 4x zoom that helps to find the measurement point in bright sunlight. It has a 30-measurement memory and takes two AA batteries. There is software that you can use to actually plot the footprint of a house as you take measurements walking around it.
What’s not to like? Well, the price is up there, and all these features add a lot of complexity. You don’t have to use them, but why would you buy one of these amazing devices and not take full advantage of its features?
Leica Prexiso iC4 iPhone Connector
I couldn’t resist adding this to the list! It’s a plug-in device for an iPhone that converts it to a laser measuring tool. If you have an iPhone, you can bring this adaptor along, plug your phone into it, and get measurements that look professional and with a cool-looking display. It will measure only up to 66 feet, and its durability is only as good as the phone’s durability. This would not be my first choice, especially when you can get a smaller device, such as the Hilti PD5, which you can drop in your pocket, that does more, costs less, and has a better warranty.
What Some Other Pros Are Saying
There are so many choices in this product category that it is mind-boggling! This might be a case where you start out with something simple and basic like the Bosch DLR130K. Then you can decide, after using it for a while, if you need some of the other features. Bill Smith of Building Diagnostics of NH uses a Leica DISTO D5 (similar to the D8). He says, “I frequently use the addition function to work around obstacles, and the inclinometer feature is invaluable for checking roof slopes. The target function really helps when working at long distances, too. I really like being able to measure to peaks and eaves without having my tape buckle as I extend it or having to get a ladder. It's a lot safer when working near service entrance cables, too.” Bill advises taping a target on a corner to ease length measurements.
Eric Frick of Mosby Building Arts has used laser measuring tools for years. Since 2009, he has been using the Bosch DLR165 and the Bosch DLR130K. He feels that both of these measuring tools have “good value to cost and good options, and Bosch is a good brand.” He feels they improve his accuracy, particularly in ACH calculations.
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