View Full Version : HVAC Duct Layout

October 3rd, 2003, 12:18 AM
I'm confused and maybe someone can help.

We built a new house and one end of the house is cooler than the other. The south end is the hottest. The house is a month old, full brick and we paid to have "upgraded" insulation(yes, it was installed).

If you look at how the ducting is done, the duct from the blower is fed into a box that has many ducts of different sizes coming out of it and going to each room. This box is located on the cooler end of the house. The ducts on the cooler side of the house range from 3 ft(about under the box) to 20 ft. The hotter side of the house has one large duct going about 25 ft and connect to another box and this feeds 3 rooms. The other duct on the hottest room in the house is about 1/2 the size of the other and goes about 20 ft and splits off a small duct to the entry hall and the continues about another 20 ft to the duct in the hot room. All the air comes out in the entry hall so I shut this register and more comes out in the hottest room. There are two returns. One is located near the blower with about 6 ft of duct to the blower. The other return is located about 25-30 ft away near the hotter side of the house.

I have several questions, but I guess the real one is how can I get more air to the hotter side of the house? I had Dampers installed, but I could shut off everything on the cool side of the house and all that would happen would be that the cool side got warmer.

Why is the boxes that the ducts come off of not centralized and the ducts made to somewhat of a consistant length to get more even air distribution?

October 4th, 2003, 11:17 AM
Installing a hot and cold air duct system for a central heating system is an art using calculations and site specific custom design for each house being heated. There is no one way to do this heating system.

The goal is to design the heat so that the bedrooms are a bit warmer than the living areas and the living areas are a bit warmer than the storage areas and the garage has its own heating system with no common ducting between house and attached garage.

Much depends on if your furnace is central inside the house or on one end. How big the house is. How many floors and what type room use on each floor and heating degree days in your area. All the above makes a big picture for consideration of heating and return air duct design.

I suggest you have a heating PROVEN TRAINED EXPERT come to look at you ducting design. May be your heating company did it right in the first place and you shutting off heat ducts is messing the entire system up. Do not hit and miss and guess. Get some proven skilled help to look at your system and evaluate what you have. Ask for formal schooling credentials, not just how many years they have been doing it right or wrong depending on who is doing the judging.

Bigger houses have a single trunk line ran the length of the house with sized off shutes to each room in specific defusser design. A flat wall with a reduced heat duct coming though that flat wall of the trunk line will experience a stop of air flow due to a flat wall the air hits blocking most air flow going out that smaller duct in the end of that squared off duct. A defusser squeezes the air flow gradually causing the air to increase in velocity of air flow when the reduction is gradual. Many things in teh design of a heating duct system will ruin the profeciency of that duct system. The worst the effeciency design the higher the monthly heat bills. Money well spent hiring a proven formally schooled heating expert or heating engineer to come and look over your design to find if done properly as an overall picture. May be the difference between a huge monthly heat bill due to poor duct design or a heat bill 25% of that higher heat bill or less due to proper duct design.

Call for an opinion on your design let us know what you find.

Good Luck