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US Mechanical Services, PO Box 112, Mount Prospect, IL (2026)

12/20/2021

Furnace Heat Exchanger Testing

The first rule for checking a heat exchanger is to always follow the manufacturer’s directions for testing heat exchangers. Another good source of information is the AHRI Guidelines. Testing and verifying that the heat exchangers are solid with no holes, cracks, or voids should be done on every maintenance.

A couple of things worth mentioning:

Most heat exchangers are at a negative pressure in reference to the air moving over the heat exchanger. This means that the air from the return will move into the exchanger, rather than combustion gasses moving into the airstream. This means that a crack doesn’t always mean that there is CO in the air.

As long as we have complete combustion, there shouldn’t be any significant CO (Carbon Monoxide) in the flue. Under 100 PPM air free and stable is acceptable. To be clear, if there are any cracks in the heat exchanger it needs to be replaced.

If we rely on only a visual inspection to find an issue we can easily miss problems (including cracks) that our eyes can’t see. So here are some suggestions on how to find cracked heat exchangers and other furnace safety issues.

Ambient Carbon Monoxide

One of the first things you should do is measure ambient CO with a combustion analyzer in the conditioned space while the heat is running. Anything other than ZERO ambient carbon monoxide is worth investigating. This doesn’t mean that the furnace is necessarily at fault. Keep in mind, smoking indoors or cooking can increase ambient CO above zero but if you see it, take the time to investigate.

Flame Displacement

One of the oldest ways to check for heat exchanger cracks is to simply observe the flame when the blower starts. Most furnaces will have a blower delay allowing the heat exchangers to become warm before the blower starts. This procedure is as simple as watching the flame and observing if the flame moves or changes when the blower starts.

Because the burner is isolated from the indoor airstream, there should be no change in the flame when the blower starts. If there is, start looking for a crack or leakage between the heat exchanger and the air stream.

Combustion Analysis

Testing combustion won’t necessarily tell you if you have a crack, but it will tell you if you have high CO. Testing will verify that the equipment is operating without CO.

Exchanger Isolation Pressure Test

When you suspect the system may have a defect in the heat exchanger, another test you can do is place a manometer probe in the exchanger and seal off the inlet/outlet of the exchanger as best you can (make sure the gas is off). Next, turn on the blower and see if there is a change on your meter. Any change indicates a heat exchanger leak.

Visual Inspection

In some cases, a traditional visual inspection makes the most sense. You can inspect by either removing the blower or the high limit (or both) and use a mirror or scope to inspect. When you do find a crack, the furnace should either be repaired or replaced

If you do find exchanger cracks on newer units you should also look for causes like low airflow, incorrect or***ce size, or over firing that could have caused the issue...

https://www.famous-supply.com/heat-exchanger-testing-10-13-2020

10/28/2020

As a sales manager for the plumbing, heating and appliance supplier Ferguson Enterprises, Phillip Carr witnessed escalating demand for appliance repair early in the pandemic. He sold to builders, so he had already seen how fragile the global supply chain has become. Then the machines — and the parts that compose them — became scarce because of trade disputes with China and Germany, shuttered factories and manufacturers converting to make protective equipment. He decided to go over to the other side — where the jobs were.

“It used to be if an appliance got damaged but was still workable, the customers would return it to get a new one. They don’t do that now because there’s no new ones to get,” Carr said. “So that’s added to the amount of repairs that need to be done and backing up repair people as well. Because if it’s working, people are going to have to keep it.”

Amid the general collapse of the service economy during the pandemic — think retail or restaurants — appliance repair technicians are seeing explosive demand for their services as families adjust to living at home 24/7, sometimes with adult children, elderly parents or in-laws expanding households and putting more wear and tear on refrigerators and dishwashers.

For people like Carr, who was at risk of reduced earnings or even losing his job, it is proving to be an elusive bright spot in an otherwise devastating labor market — and with long-term potential.

Gone are the days of the lonely Maytag repairman. The repairman of 2020 — with few exceptions, it’s still most often a man — has been working nonstop for the past seven months as the suddenly homebound find themselves cooking and laundering more than ever.

The strain of relentless domesticity is showing up in overworked or, in some cases, previously untouched appliances. America’s stay-at-home workers have had to deploy ovens used to store shoes to actually cook meals. Fridges are constantly mined for snacks, and dry-cleaned suits have been replaced with day pajamas that double as napkins. The machines can take only so much.

A broken device can push a strained family over the edge. Repair technicians — when they can be booked — can take over a month to fix a much-needed machine.

Take Carl McCarthy’s dishwasher in his weekend house in the Catskills. In 12 years, it never saw daily use. Then the novel coronavirus hit, and his family decamped from Manhattan. Nonstop service for four people broke the old Kenmore, and they waited over a month for it to be repaired.

“We had to do dishes by hand, and it proved to be too much for the family to handle,” McCarthy said. “One day I bought a huge plastic trash can and tons of paper plates, disposable plastic cups and cutlery and hid all the real dishes and cutlery.”

After learning the key part would take weeks to arrive if ordered from the manufacturer, McCarthy tracked it down for $12 on eBay. Another visit from the repairman and the family escaped dirty dish purgatory.

The covid-19 recession is the most unequal in modern U.S. history

As similar scenes play out across the country, repair companies are triaging calls, hiring new employees and navigating backlogs from the broken supply chain for parts.

After witnessing this from the outside, Carr took the early retirement option to start his own business. In August he enrolled in the three-week Dyer Appliance Repair Academy course in a Fort Worth, Tex. suburb, where students learn the trade of fixing refrigerators, dishwashers, ovens, washing machines and dryers.

Now 60, Carr plans to work for another five to seven years. He sees opportunity, not just for him but for two sons in their 20s. One is finishing his degree and entering an uncertain job market; the other has a hotel service job.

In his August cohort, Carr learned alongside three military guys transitioning into civilian life, two people with some repair experience but not enough to get a full-time job and someone in law enforcement.

Since then, it’s all been moving faster than he expected, as he’s trying to get his website up and contract with manufacturers. He’s constantly fielding calls from people who need repairs. In fact, when he went to Verizon to hook up a phone for his newly minted company, the salesperson said: “I need to talk to you because I had to try to fix my own appliance because I couldn’t get it done.”..

With supply chains snarled for new machines and washing machines, dishwashers and other home goods experiencing heavier use, the pandemic has led to a surprising boom in the struggling appliance-repair industry

09/03/2020

Just been better since 1967 - HVAC tools, valves & fittings.

07/12/2020

Air Conditioning May Be Spreading COVID

July 8, 2020 -- As COVID-19 cases rise rapidly throughout the South, some scientists believe there could be an important, but overlooked factor in the spread of the virus in the region--air conditioning.

Just as chilly winter temps create the perfect conditions for passing colds and flu—driving people indoors and into closer proximity for more hours of the day where it’s easy to swap germs, researchers believe broiling heat in the southern U.S. could be having the same effect, sending people indoors where whirring air conditioners are running full blast.

“You go indoors for the cool, just as in the northeast and other cool places you go in for the warmth in winter, so you’re less socially distanced,” says Edward Nardell, MD, professor of environmental health and immunology and infectious diseases at Harvard’s T.H. Chan School of Public Health. “You’re more likely to be touching the same surfaces that have been contaminated by people speaking and coughing etc.,” he says.

And that’s not the only problem.

Air conditioning is also risky because of the way air handlers work. When outdoor temperatures are extreme, HVAC systems adjust the mix of fresh air they pull in to save energy. That means the hotter it is outside, the more indoor air recirculates, which means, “You’re breathing a higher percentage of the same air that other people are exhaling,” Nardell says. If someone in the building is shedding the new coronavirus, it can build up in the recirculated air.

And this may seem obvious, but air conditioners have fans that blow the air around. That gives the smallest viral particles—aerosols--extra lift to say suspended in the air for longer. “The air currents that are produced by air conditioners and also fans and other air moving devices can carry particles further than they might otherwise go,” he says.

Air conditioners also remove moisture from the air, “and we know viruses prefer dry air,” he says. In certain situations, that combination of factors may create the perfect conditions for contagion.

Emerging Evidence Points To Airborne Transmission
Studies of air conditioning come as more evidence emerges about airborne spread of COVID-19. In a commentary published this week in the journal Clinical Infectious Diseases, an international group of 239 scientists have appealed to “national and international bodies” including the World Health Organization, to recognize this potential for airborne spread...

As COVID-19 cases rise rapidly throughout the South, some scientists believe there could be an important, but overlooked factor in the spread of the virus in the region--air conditioning.

04/22/2020

Ground - In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth.

Electrical circuits may be connected to ground (earth) for several reasons. Exposed metal parts of electrical equipment are connected to ground, so that failures of internal insulation will trigger protective mechanisms such as fuses or circuit breakers in the circuit to remove power from the device. This ensures that exposed parts can never have a dangerous voltage with respect to ground, which could cause an electric shock if a grounded person touched them. In electric power distribution systems, a protective earth (PE) conductor is an essential part of the safety provided by the earthing system.

Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices. In some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor (see single-wire earth return).

For measurement purposes, the Earth serves as a (reasonably) constant potential reference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. In electronic circuit theory, a "ground" is usually idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid. Stray voltages or earth potential rise effects will occur, which may create noise in signals or produce an electric shock hazard if large enough.

The use of the term ground (or earth) is so common in electrical and electronics applications that circuits in portable electronic devices such as cell phones and media players as well as circuits in vehicles may be spoken of as having a "ground" connection without any actual connection to the Earth, despite "common" being a more appropriate term for such a connection. This is usually a large conductor attached to one side of the power supply (such as the "ground plane" on a printed circuit board) which serves as the common return path for current from many different components in the circuit.

Long-distance electromagnetic telegraph systems from 1820 onwards...

More: https://en.wikipedia.org/wiki/Ground_(electricity)

04/22/2020

Three Phase Ellectric Power is a common method of alternating current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. It is also used to power large motors and other heavy loads.

A three-wire three-phase circuit is usually more economical than an equivalent two-wire single-phase circuit at the same line to ground voltage because it uses less conductor material to transmit a given amount of electrical power. Polyphase power systems were independently invented by Galileo Ferraris, Mikhail Dolivo-Dobrovolsky, Jonas Wenström, John Hopkinson and Nikola Tesla in the late 1880s.

Advantages

As compared to a single-phase AC power supply that uses two conductors (phase and neutral), a three-phase supply with no neutral and the same phase-to-ground voltage and current capacity per phase can transmit three times as much power using just 1.5 times as many wires (i.e., three instead of two).

More: https://en.wikipedia.org/wiki/Three-phase_electric_power