The next time your customers are trying to explain their comfort issues relating to their thermostat, help them out by mentioning the term Thermostat Wars. It will usually bring a smile to their faces, and will let them know you understand what they’re living with. The best method to diagnose this very common problem is to provide simple testing with an infrared thermometer to shed some light on the comfort issues, and offer a short lesson on how a thermostat senses temperature.
Ideally, temperature variation throughout a building should be less than 3F. However, after a short hunt around a typical home or office, you’ll find this is an aggressive goal, as temperatures may vary as much as 10F degrees throughout a building.
Temperature Test Locations
Start by defining where to read temperatures with your infrared thermometer. The rules to follow for accurate, consistent temperature reading in a room are to shoot the temperature of each room in the same location that you would consider placing a thermostat. (Click here for an example.)
Measure the room temperature on an inside wall, An outside wall temperature is subject to the outdoor temperatures, and will often be 3F to 8F warmer or cooler than the core of the building.
Test at chest height; 4- to 5-ft. above the floor is ideal. Heat rises, so during heating or cooling season the temperature difference between the floor and ceiling will frequently be 3F to 6F different. If the building has a poor thermal envelope, this difference can be up to 10F.
Measure an average room temperature away from the flow from a supply register. If it’s doing its job, a register will cause very fast changes in the air temperature, and can give the equipment the idea that it’s performing far better than it really is. The result will be very short cycles and very high operating expense. Most cooling systems need to run upwards of 10 minutes before they reach peak operating efficiency. A 14 SEER system has an operating cost of an 8 SEER if it’s cycling every five minutes.
Also, be sure to test away from a heat source such as kitchen appliances, computers or lamps. Consider where the rays of sun will hit during the day. It’s not uncommon for direct sunlight through windows to heat indoor surfaces to over 100F, even in winter months.
It’s easy to assume the temperature is the same inside the wall as it is on the outside. But often walls have electrical or plumbing penetrations that allow outdoor air temperatures to creep into the building and have a significant effect on the thermostat by heating or cooling the wall cavity behind the thermostat.
The primary defect that exaggerates this situation is an oversized hole for the thermostat wire behind the thermostat. Often, these are oversized to allow the installer to fish the stat wire through the wall. This allows the outside air in the wall to affect the temperature sensing device in the thermostat and make it read a completely different temperature than the air temperature in the room. Stuffing insulation in the oversized hole alone is an inadequate patch because airflow flows through insulation. (Insulation is often made of fiberglass, the same material many air filters are made from.) Repair these holes with liberal dose from a can of closed cell foam.
Masonry walls create problems of their own when it comes to thermostats. After a setback cycle it may take a masonry wall two or three hours to adapt to the air temperature of the room. Meanwhile, the equipment will be cycling continuously in response to calls from a thermostat that constantly swings back and forth as it’s cooled by the air temperature, and then is quickly heated by the wall (vice-versa during winter months).
Add an Insulated Base
The only solution that has stood the test of time for masonry walls or walls affected by outdoor temperature is to install an insulated base between the thermostat and the wall. This will allow the thermostat to sense the air temperature of the room by breaking its contact with the wall.
These insulated bases can be made from a 1-in. thick piece of foam insulation board covered with a good quality piece of 1/2-in. hardwood plywood and finished around the edges with a matching wood trim. It can be stained to match the finish of the building. Because these are custom-made system accessories the margins can be quite handsome, and customers appreciate the comfort solutions found through imaginative diagnostic testing. Many people have suffered with this problem for decades without ever being offered a solution.
With the significant increase in real estate prices over the recent years, good contractors willing to offer a higher level of services are finding homeowners increasingly willing to spend significantly more money to obtain true measured comfort and performance.
There is a new level of comfort being defined by contractors willing to solve problems past the heating and cooling boxes and address air distribution and system performance issues. As energy costs are increasing, homeowners and commercial building owners are looking for someone willing to do more than stick in a new box and insinuate the laboratory measured efficiency of the equipment will solve their comfort and energy expense issues.
The thermostat is a great place to begin the search for solutions beyond the box.
Rob “Doc” Falke serves the industry as president of National Comfort Institute a training company specializing in measuring, rating, improving and verifying HVAC system performance. If you're an HVAC contractor or technician interested in instructions for building an insulated thermostat base, contact Doc at [email protected] or call him at 800/633-7058. Go to NCI’s website at www.nationalcomfortinstitute.com for free information, technical articles and downloads.