Why would anyone do this?

Specific Inspection Topics Inspecting HVAC Systems
1

Did an Energy Audit for a friend yesterday, and found the most unusual installation: A 4" insulated duct directly from the outside air to the cold air return. The hot air coming out of the registers only got about 85-95 degrees, which seems a bit cold to me. The exterior air temperature was about 20 degrees, which would have an alarming affect on the temperature of the heated air. The furnace seamed to run allot and do take about 10 minutes to raise the temp 1-2 degrees.

This is a High efficiency furnace, properly vented, in the tightest conventional house I have ever seen. Did the furnace guy install this to allow more fresh air in the house? I seriously think it is overkill, and should be eliminated.

Input please.

2

That would not be an unusual install in my area.

The discharge air temp does seem a bit low however.

3

With the tight homes now days, this is part of the ventilation system.

AHJ looks for it around here.

4

As to the “why” the dryer, bath exhausts, water heater, fireplaces and range hood all remove air from the structure.

A fresh air intake duct connected to a return air or simply dropped near fuel burning appliance such as a water heater serves as the makeup air source.

5

OK, I can see why fresh air. TY fellas.

A 4" duct is allot of really cold air, I suppose I could cover it for a cycle, and see if it improves the heated air temperature.

Any other ideas on how to increase the temperature?

6

Should be a balancing damper there for control, but it will only take in the same amount of air the house leaks to the outdoors anyway. It could be 16 in duct and it would draw the same.

Seeing this is a super sealed house it is required.

7

There is a fresh air supply system with a motor actuated damper controlled by an interior, centrally located dehumidistat. If the HVAC calls for heat and the dehumidistat is satisfied, no additional outside air is introduced to the house…this system saves heat by supplying air only when necessary and not necessarily each heating cycle.

Another system based on a similar fresh air duct is the “AIR CYCLER”:

8

**Field Controls has a make up air system that meters the amount of air entering the house. http://www.fieldcontrols.com/cas.php

Even so called tight houses do have leakage. By making the house very slightly positive cold drafts can be reduced.**

9

They just don’t get it, do they? From the Field website:

  • “The Field Make-Up Air System solves the “sick house syndrome” caused by too tight home construction.”*
    **
    Tight home construction is much more energy efficient!! And reducing air leakage reduces/prevents interior moist air from getting into attics & walls where it may condense. The tighter the house is the better…just got to learn how to run the house and ventilate the interior.