This article was originally published in the July/August 1999 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online July/August 1999

Training Made Easy 
The Telltale House 

by Ann Kelly and David Keefe

David Keefe, senior energy analyst with Vermont Energy Investment Corporation, is the lead technical trainer on The Telltale House project.

In exhibit halls, The Telltale House attracts crowds instantly. But this versatile traveling exhibit is proving just as popular at specialized trainings for all types of building professionals.
The fireplace in The Telltale House is equipped with a smoke generator and a heat source that produces a natural draft. When the room becomes depressurized, smoke will backdraft down the chimney and into the room (right), just as it would in any home. 
Air leakage sites in the ceiling and walls of The Telltale House are identified by shiny, multicolored pinwheels that spin whenever air passes through these holes.
The Telltale House can easily be set up for pressure diagnostic training. The blower door is subsituted for the range and exhaust hood that normally occupies this space in the kitchen/living room.
It's been over a year now since Home Energy and Affordable Comfort, Incorporated launched The Telltale House, a traveling exhibit that demonstrates how HVAC systems, exhaust fans, and combustion devices interact in a typical home. During its busy cross-country journeys, our custom-built model house has been a resounding hit at more than 15 sites, from the largest builders' shows in the nation, to local home shows for the general public (see Telltale House Revealed, HE July/Aug '98, p. 11, and Spreading the Word in San Francisco, HE Sept/Oct '98, p. 10). The flexible design of the exhibit makes it possible to use it for simple demonstrations showing how a house behaves as a system, or for specialized training in such areas as pressure diagnostics and combustion safety. Seeing is Believing The great appeal of The Telltale House is its ability to dramatically illustrate complex concepts about air pressure in houses by making air movement visible. With the flip of a few switches, the exhibit can simulate conditions that cause a water heater to backdraft poisonous combustion gases, for instance: Theatrical smoke shows gases flowing up and out the flue, then suddenly reversing direction and spilling back into the house. The reason? A leaky duct, or perhaps an exhaust fan, has caused the air pressure in the room to drop, creating enough suction to pull air--and all the combustion byproducts it contains--down the flue and into the room. A similar demonstration can be done showing why smoke from a fireplace might spill into the living room instead of exhausting up the chimney.

The exhibit also uses colorful metallic pinwheels to show air flow through leaks in a house envelope. Each pinwheel is mounted on a ceiling or wall next to a hole that represents typical air leakage. Whenever there is a pressure imbalance in the house, air is forced in or out of some of these holes, causing the glittery pinwheels to spin. As the spinning starts or stops in different parts of the house, the observers can easily see the surprising, often erratic, way air moves swiftly through the entire house under dozens of everyday circumstances.

This frequent movement of air into, out of, and throughout a house is hardly ever noticed by its occupants. Yet, this air movement is responsible for drafts, for wasting energy, for backdrafting combustion appliances, and for circulating moisture and pollutants. When air flow is made visible, viewers are generally astonished to see how common situations--like a closed interior door--can create uncomfortable, unhealthy, and even dangerous conditions in an average home.

All of these problems are becoming more common, hazardous, and costly as construction methods improve to make homes tighter. However, there is currently very little awareness in the building industry of the causes and cures for these performance problems. One reason is that few builders or contractors look at a house as an integrated system. But, judging by the amazed reactions to the exhibit that we've observed, that perspective can change immediately after a Telltale House demonstration. That really happens in a house? is a typical response from onlookers before they begin a barrage of questions. For many in the building industry, the big lesson of The Telltale House is finally discovering an explanation for some puzzling situations they've encountered in houses they've built, repaired--or even live in.

From Awareness to In-depth Training To date, at least 3,000 people have seen some variation of a Telltale House demonstration. Some of the stops on The Telltale House's itinerary were conferences with large trade expositions where our exhibit had to compete for attention with hundreds of others. In these busy settings, people who stopped at our booth got a short demonstration of five to ten minutes. On several occasions, though, The Telltale House was prominently positioned in a special demonstration area in or near the exhibit hall. Here we could conduct longer, more involved demonstrations lasting 20 to 45 minutes.

Given such widespread visibility, it's not surprising that the demonstrations eventually caught the attention of industry representatives responsible for training programs. They immediately saw the benefit of being able to view problems like backdrafting at no personal risk, and to actually observe the invisible effects of air leakage and unbalanced heating and cooling systems. Inquiries began coming in to use The Telltale House to train service technicians, HVAC contractors, home inspectors, manufacturers' sales staff, installers, builders, and weatherization personnel, among others.

As a result of this interest, at some conferences the exhibit began to appear in workshops rather than on the floor of the exhibit hall. At Comfortech, a conference for residential heating and air conditioning contractors, we gave a series of 90-minute presentations that went into great detail on how air moves in houses and what situations lead to backdrafting. In these sessions, we had the opportunity to demonstrate an optional feature of the exhibit: how to measure house air pressures using diagnostic tools such as a blower door and manometer.

We also gave in-depth presentations at more specialized events, such as the Vermont Star Homes conference, which is mainly for builders. There the focus was on how to take envelope tightness into account when planning for mechanical ventilation systems, indoor humidity control, and air intake and venting for combustion appliances. At this event, as well as at the Northeast Sustainable Energy Association's conference and a conference on building high performace homes in Green Bay, Wisconsin, The Telltale House was used on the exposition floor for demonstrations and to attract participants to our workshops, which covered a range of topics related to the exhibit.

Longterm Training The most extensive use of The Telltale House was at Pacific Gas & Electric Company's Training Center in Stockton, California. There, for a two-month period, the exhibit became an integral part of a state energy code compliance program to qualify HVAC contractors on a new duct-sealing require- ment. For this type of extended stay, one of our Telltale House technicians provides a train the trainer session on how to set up and operate the model so that it meets the customized needs of the client.

At PG&E, diagnostic trainer Gary Fagilde was able to use The Telltale House in his classroom presentations to cover the following situations in great detail:







  • the pressure effects of dominant supply and return duct leakage;

  • a dominant return leak in the combustion appliance zone vs. equal leaks in both the supply and return ducts (fixing only the supply side leakage can create depressurization in the utility closet, where combustion products can be drawn into the return duct and circulated into the living space);

  • depressurization of the combustion appliance zone;

  • the communication of combustion byproducts with the house air through a return leak in the utility closet;

  • depressurization caused by closing interior doors, and how this causes spillage and backdrafting of the fireplace;

  • attic fan depressurization of the conditioned space; and

  • how kitchen exhaust fans can depres- surize conditioned space and how an oversized fan can cause the fireplace to backdraft.
It takes many hours of classroom lectures to describe what The Telltale House shows in just a few minutes of operation, says Fagilde. This tool really expedites the training process. Time for More Telltales? When the Environmental Protection Agency (EPA) funded The Telltale House project in 1997, our goal was to expose a widespread audience to energy-efficient, healthy building principles in an effort to spur changes in the marketplace. But we knew that market transformation would not be accomplished simply by raising awareness at bustling expositions where just about everyone is experiencing sensory overload. Any real change would entail moving the industry to the point where the products and services involved in high-performance homes were valued, available, and in demand by consumers. That in turn would require the emergence of a workforce of trained personnel who could deliver on promises of safer, more comfortable homes. When The Telltale House project was conceived, we anticipated a demand for specialized training, and the requests we've received from different segments of the industry are a good indication that the marketplace is responding.

In fact, the growing demand for training could mean that The Telltale House itself might experience a market transformation, enabling the project to become self-supporting when EPA funding runs out this summer. Already, a number of private companies have expressed interest in purchasing an exhibit for permanent use in their own training programs. And, if we had more than one exhibit available for lease, we would be able to respond to the many requests now turned down because of scheduling conflicts.

Currently we are exploring the feasibility of building a second-generation Telltale House that could be manufactured and sold in quantity. With more Telltale Houses being used for training on a regular basis throughout the country, there would be greater hope for a genuine shift in the market toward high-performance homes.

We are anxious to have the project continue and to see it flourish. So let us know if you are interested in having The Telltale House pay a visit to your next conference, workshop, or training session, or if you would like to order a Telltale House of your very own. For more information, call Helen Perrine at Affordable Comfort at (800)344-4866.

The Telltale House

The Telltale House is an interactive exhibit used to demonstrate how air pressure affects the environment inside homes. The large plastic display contains three rooms--a kitchen/living room, a utility closet, and a bedroom--plus an attic. It measures approximately eight feet tall, eight feet wide, and three feet deep.
In the kitchen/living room there are models of (1) a range with a simulated exhaust fan, and (2) a fireplace that can emit theatrical smoke. When activated, the smoke is visible in the firebox area and through the clear plastic chimney. (3) A water heater in the utility closet is also equipped with a smoke device and a see-through flue to show the movement of combustion gases. In this same room, there is a model of (4) an HVAC system with a fan in the air handler that mimics a circulating fan in an actual HVAC unit. (5) A single control panel on the front of the exhibit has on/off switches for the fans, the smoke generators, and the lights used in the house. In the kitchen/living room, the range (1) can be replaced with a blower door (2) when The Telltale House is used for pressure diagnostic training. Note that the single return register (3) for the whole house--a situation common in many homes--is located in this room on the wall bordering the utility closet. An operable sliding door (4) leads from the kitchen/living room directly into the L-shaped bedroom, which extends behind the utility room and opens to the front of the exhibit.
The supply register (left) in both the kitchen/living room and in the bedroom have streamers attached to indicate when the forced air heater/air conditioner is operating. Another type of air flow indicator, shiny metallic pinwheels (right) are mounted on the ceiling of each room and on the outside walls of the kitchen/living room, the bedroom, and the attic. Whenever air moves in either direction through these holes, the pinwheels spin and glitter, making it easy to actually see air leakage in a house. In the attic there are ducts that run from the HVAC unit in the utility closet below to ceiling supply registers in (1) the kitchen/living room and (2) the bedroom. 

Mounted on the wall at one end of the attic is a fan that simulates a powered attic exhaust fan (right). On the opposite wall there is a (3) hole representing an attic vent.



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