Mechanicals/ HVAC System

Detailed Mechanical Schedule

Why is it important for M-T-N Design to include a detailed mechanical schedule for your custom home?

Loosely sealed / non-efficient homes leak in the energy envelope allow conditioned air to seep out and unconditioned fresh air to flow in. With tightly-sealed energy efficient homes conditioned air stays inside and unconditioned fresh air stays out.

Contact Us


Get To Know Your HVAC

Heating Examples: Heat Pump, Furnace, Radiant, and Fireplace

Ventilation Examples: Ducts, Vents, Heat, Energy Recovery Ventilator, Dehumidifier, and Humidifier

Cooling Examples: Heat Pump, Air Conditioner, and Swamp Cooler

Results Of

Tight Construction & Poorly Designed Mechanical System 

Interior Moisture:

If water vapor is allowed to build up, it can cause health issues and promote mold growth

  • 5 Minute Shower = 0.5 Pints
  • Humans = 0.4 Pints Per/Hr
  • Cooking = 1.2 – 1.5 Pints
  • Washing Dishes = 0.7 Pints
  • 5-7 House Plants = 1 Pint A Day

Rish To Air Quality:

Without proper ventilation, indoor pollutants can get rapped and cause health issues

  • Mold Growth
  • Carbon Monoxide
  • Dander / Dust
  • Volatile Organic Compunds 

Unstable Pressure:

The air pressure within the home is constantly trying to match the outdoor pressure. Without proper ventilation, indoor air pressure can compress or expand. This causes drafts between rooms and  reduced effectiveness of heating and cooling units.

Your Building Team

Who is responsible for your HVAC System? 

  • Designer / Architect: Sets location of mechanical room(s) specified a building system
  • Manufacturer Of Building System: Knows the capabilities of their materials and how they will affect the tightness of the home
  • GC / Builder: Must prepare for HVAC installation needs – usually responsible for purchasing the system
  • HVAC Supplier / Installer: The company or companies you buy the system from and the technician responsible for installation

Simplistic HVAC Sizing Approaches

“Rule Of Thumb” Sizing Charts

Step 1: Select the climate ZONE where the home is located (map provided)
Step 2: For AC Units – Find the square footage range of the house
Step 2: For Furnaces – Multiply the square footage of the house by the BTUS listed for your climate zone
Step 3: Select a unit that meets the Tons or total BTUs of your calculation

Stand across the street and whichever cut-out the home fits into is the approximate size.

  • While homes have become more and more energy efficient HVAC charts have not changed
  • Some HVAC installers ignore all factors but home size “2,500 Sq.Ft. is 2,500 Sq.Ft.”
  • Many HVAC installers simply select the largest unit in the scale “Just to be safe”

What can happen when your system is oversized? 

Loss of Comfort

Air conditioners dehumidify air, unless they short cycle. Short cycles do not run long enough to remove moisture. Oversized furnaces heat unevenly making some rooms warmer than others. You may experience variances in air pressure from room to room.

You Pay More

Larger units cost more upfront. Oversized units short cycle – turning on and off more often – which uses more energy than long cycles do. Units that do not function as intended can break down or wear out more quickly. 

Unhealthy Environments

Short cycles can reduce the system’s ability to properly cycle air, keeping indoor pollutants from being expunged. If your system is unable to cycle out moisture, mold can develope and cause health issues.

Whole-Home Sizing Approach

Request these specifications with your construction documents

Created by ACCA (Air Conditioning Contractors of America), these manuals are the ANSI-recognized national standards for HVAC Design.

The Manual J calculates the heating and cooling loads for the entire house, as well as room-by-room calculations. Without room calculations, it’s impossible to design a proper distribution system. Room-by-room Caluculations:

  • Determine the possible need for zones
  • Determine the amount of air needed in each space to “balance airflow”

The manual S utilizes the loads calculated in the manual J to determine the optimal equipment specifications for your system. The specific purpose is to prevent under and over sizing of your equipment. It also instructs designers how to interpret equipment manufacturer’s specifications.

The manual D uses the calculations from the manual J to ensure that ducts carry the right amount of air, at the tight speed, into each room. Wrong size and configuration of ducts may cause: 

  • The room to be too warm or too cool
  • The air to be drafty
  • The air to be too noisy and drown out conversations, music, or television
  • The air to move slowly, keeping conditioned air from circulating or mixing well in the room
  • The fan to work harder, fall sooner, and expend more energy
  • The furnace or air conditioner safety devices to stop
  • Pressure differentials that may increase energy costs and cause discomfort

The Result Of Using A Whole-Home Approach

Your Team Will Be on the Same Page Through The Entire Build

Your System Will Be Optimized for:

  • Comfort
  • Cost
  • Health



Interested in Learning More About Building Your Forever Home?

Contact Us Request Literature