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Mr. Heat Mechanical Inc. Heating Cooling Electrical Hydronic Contractor Official Website

What Happens When a Coil is Loaded with Dirt?

dirty evaporator coilFinned tube coils are meant to have contact with the air flow, as more contact creates more heat transfer. Heat transfer is nothing more than heat exchanged from one medium to another, and the goal is to create maximum heat transfer efficiency. The downside to this process is the coil’s susceptibility to foreign materials becoming lodged in them. The following explores this problem in a little more depth.

Tubes in a coil are the “primary surface”, and the fins are the “secondary surface”. In a heating coil, the water or steam is hotter than the air going across the outside finned-tube surface. The heat is removed from the fluid and transferred to the air. In a cooling coil, the water or refrigerant is cooler than the air, and the heat from the air is transferred to the water or refrigerant. All of this can be calculated by our computer coil selection programs. However, these programs are BTUH capacity based on a clean coil. The term “clean coil” means no internal or external fouling. It’s like the miles per gallon you see on a new car sticker that represents a perfect test versus the results you get with normal driving. The same goes for coils.

Finned Tube Fouling

As stated, the finned tube design is meant to have maximum contact with the air. Because of this, internal portions of a coil core can begin to “load up” from dirt and debris. Most times, it’s because the upstream filters have not been changed or are inadequate for the system. Many systems still have the old type furnace filter which is equal to a MERV 6 rating. Even MERV 8 filters are not adequate for most HVAC systems. They do not remove enough particulate, especially when they’re not replaced on a regular basis. This will “load up” the downstream coil.

When a downstream coil is loaded, the air resistance is increased. The system was sized for an internal unit resistance, and one of the main resistances in an air handler is the coils. The air flow amount can fall as much as 15% to 25% based on this fouling. Many operators see this decrease and speed up the fan to overcome the added resistance. This only adds to the operating cost of the unit, as the brake horsepower and overall power consumption will increase substantially.

The coil also has more “insulation” between the fluid inside the tubes and the air outside the tubes.  The dirt will act as an insulating pad between the two streams, and you can lose 10% of your heat transfer due to this factor. The dirt buildup isn’t always uniform across the entire face of the coil.  We’ve seen water carryover in cooling coils, because a local velocity through a more opened area of the coil rises above the velocity where carryover can occur.

Tube Side Fouling

The inside header and tube surface of most coils installed in today’s HVAC systems are not cleanable.  Many systems are not pure water, steam, or refrigerant; and the inside surface can cause performance problems. This is usually unknown, as you can’t see inside a coil unless you disconnect the coil connections. It may still be difficult, as you will only be able to see a few inches into the coil.

Water (glycol) and steam are both treated. Sometimes there is also a lack of treatment that is every bit as bad. With these treatments, the fluids can begin to have clogging affects with the inside tube surface. Condensate especially can almost close tubes after a long time in service. It’s important to understand that the internal fouling acts as an insulator between the fluid inside the tubes and the air outside the tubes. The capacity can be severely reduced.

Source : usacoil .com


List of approved Enbridge home energy auditors

Canada Energy Audit Ltd.

  • Phone : 1-888-298-9458
  • Email : info
  • Coverage : Greater Toronto Area | Niagara | Simcoe/Barrie | Ottawa | Dufferin | Peterborough

The Home Inspectors Group Inc.

  • Phone : 1-866-907-9206
  • Email : audit
  • Coverage : Greater Toronto Area | Niagara | Simcoe/Barrie | Ottawa | Dufferin | Peterborough

Energuy Canada Ltd.

  • Phone : 1-888-442-9577
  • Email : office
  • Coverage : Greater Toronto Area | Niagara | Simcoe/Barrie | Ottawa | Dufferin | Peterborough

Enertest Corporation 

  • Phone : 1-877-327-1504
  • Email : information
  • Coverage : Greater Toronto Area | Niagara | Simcoe/Barrie | Dufferin | Peterborough


  • Phone : 1-877-580-2582
  • Email : info
  • Coverage : Greater Toronto Area | Ottawa | Peterborough
Pro Home & Building Inspections Inc.
  • Phone : 416-651-7778
  • Email : prohomebuilding
  • Coverage : Greater Toronto Area | Niagara | Simcoe/Barrie | Ottawa | Dufferin | Peterborough


The Effects of Coil Selection with Outside Air Loads

HVAC and process heating/cooling must deal with the added tonnage created by using fresh air from outside. Most times, the requirement for fresh air is mandatory and can go from 10% all the way to 100 % of the system air flow. There are numerous rules and regulations written to eliminate air flow quality problems, including bacteria and other micro-organisms, that can cause health problems. Rarely is a system designed with more fresh air introduction than is required by law.

We have all heard the term “economizer”. However, many in our industry do not really understand this term. An economizer is used when the temperature of the outside air is at or near the temperature of the return air in the system. An example would be a design return air temperature to an HVAC unit that is 80 degrees F. When the outside air temperature is below or reaches the design temperature, some or all the return air can be exhausted (sometimes stated as “relief “), and an outside air damper opens to bring in fresh air. One must equal the other. Whatever you exhaust must be made up with the introduction of new fresh air into the system. If I exhaust 4000 CFM, then 4000 CFM must be introduced through the outside air damper.


Source : uscoil .com

Enercare 2019 Rate Increase

Enercare has just released their 2019 rental prices.  It’s a massive 4.2% increase compared to 2018 rate. See below for more information. 

New Furnace Efficiency Rating

The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) recently petitioned the US Department of Energy (DOE), asking them to initiate a Notice and Comment for Rulemaking to develop a new unified test procedure combining efficiency metrics for residential furnaces. At a high level, this new test procedure would combine the current gas (Annual Fuel Utilization Efficiency) AFUE, and electrical efficiency metrics (Fan Energy Rating) FER and standby, into a new unified metric AFUE2 for measuring furnace efficiency. On November 14, 2018, the DOE published a Notice of Petition for Rulemaking to consider this request. The comment period for this notice is open until January 14, 2019.

As part of this petition on November 2, 2018, the DOE issued an Enforcement Policy Statement for the FER regulation, which goes into effect July 3, 2019, stating that the DOE will not enforce the testing, certification and compliance requirements while the DOE considers the request from AHRI.

At this time, there is uncertainty regarding the outcome of the DOE Notice of Petition.

Some possible outcomes:

  • DOE denies the petition and maintains the current metric including the FER regulation with a July 3, 2019 effective date.

  • DOE agrees to further consider the petition and delays the enforcement of the current FER regulation while the petition is under consideration.

  • DOE chooses to open a rulemaking to develop the test procedure for a unified metric (AFUE2) and transition to a new efficiency standard. Timing for this transition is uncertain but likely 12 – 18 months minimum. While the rulemaking process proceeds, the current FER regulation could stay in effect or be suspended.

Please note that NRCan recently announced they will be implementing the FER regulation as of July 3, 2019. The AHRI petition does not affect Canada’s plans to implement FER.

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