MHC Custom Engineers All New Ductwork

With a Manual-D Design Using Rigid Metal Trunk Lines, Plenums and Transitions With External Insulation.

Duct systems are designed using a trunk and branch method, NEVER a radial method, also sometimes referred to as a spider web or spider leg design). 

The trunk and branch method allows exact control of the volume of air (measured in cubic feet per minute or cfm) delivered to each room or location and reduces the friction rate allowing for a more efficient system.  In some applications, this even allows a system with a lower capacity to comfortable heat and cool a home or office.  The result is not only a lower initial investment but long term savings on energy costs.  Many older systems and even some newer systems from less reputable contractors have been installed using a radial style and thus airflow has never been calculated and cannot be controlled. 

NO DUCT BOARD will be used.  Some contractors still use duct board which is made of compressed, glued together, glass fibers.  Duct board lends to poor installation as it is often simply cut with a knife and taped together causing the joints to split open and as a result, only lasts a few years.

Outdoor Equipment Installation:  MHC will install most outdoor units on 3” polymer pads (rather than the common 2”) and with a gravel base when possible.  This helps eliminate noise from the outdoor unit and allows for less chance of ground fluctuation due to freezing and thawing.  Heat pumps will also be installed on snow legs to allow condensation to drain to the pad or ground avoiding damage to the equipment from standing water or water that freezes in the unit during cold weather.

Liquid Propane Conversion Kits:  Gas furnaces installed for use with LP Gas will be converted for propane use with a STAINLESS STEEL conversion kit for better performance, longer life and prevention of corrosion as opposed to a standard galvanized metal kit.


Proper duct board installations must be notched, slotted, formed, glued, taped, and stapled, but most often is just cut, sprayed with glue, and taped to save time.  Even when installed correctly, duct board has several disadvantages.  

It is porous which allows a substrate for mold growth that CANNOT be removed and it will erode over time resulting in reduced air velocity, loss of insulation R-value and contamination of breathable air with glass fiber particles and mold.  Some states have already prohibited the use of duct board. MHC duct designs are custom engineered using Manual D design software and take into consideration velocity, friction loss and air quality using special design techniques such as elbow duct, turning vanes, transitions and reducers, dampers, zoning controls and designed air flow rate.


Line-Sets:  Many systems currently use R-22 refrigerant.  Newer systems use R-410A as required by the EPA.  The life of a system will be significantly reduced if these two different types of refrigerant are allowed to mix in coils and line-sets creating a sludge-like substance.  While not a common practice for most companies, MHC will replace all line-sets as possible.  When a situation doesn’t allow for replacing line-sets, a process will be performed that will flush the lines twice before any new equipment is connected.  

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