I've encountered an install of 6" duct directly connected to the outside through the rim joist and covered by a simple mess screen on the end.  The other end has been placed next to the gas furnace as make-up air.  The cold air just pours in whether the furnace is active or not.  There is a clear need for make-up air as the CAZ is very small and the DHW and furnace are next within a couple of feet of each other.  Any advice on a simple mechanical option to better regulate this situation.  (The DHW is natural draft and the furnace is power-assist.  They are commonly vented.)   

Views: 214

Reply to This

Replies to This Discussion

Let it be known common venting of power draft and natural draft appliances is against code in many jurisdictions. Are the DWH and Furnace in conditioned or unconditioned space?

The units are in a conditioned laundry area, 16'X11'X7.5'  The DHW is 36K btu & furnace 45K btu. (Dryer is electric.)

Hi Jerry, your classic can of worms.

Each of us must decide where we will draw the line, that line where we can be blamed for making conditions worse and this is one.  Any improvements on air sealing could affect that CAZ, therefore, IMO, I advise the problems need to be fixed FIRST, before I will continue with an audit.  I usually catch these with a pre-audit visit, but that's my routine.

Here is some of what you face and I'm not a pro on HVAC as Maine prohibits auditors from doing anything beyond the specified CAZ test. 

1.  Venting as Bob mentioned needs to meet code.

2.  Replacement air also needs to meet code, such as vent area, high and low vents, and outside clearance.  A 6" duct is way too small.

3.  Any mechanical solutions need to be approved for that use, no shoe strings and cloths pins.

A common recommendation is a cold air trap with a bucket or a 180° turn in the incoming duct.  The short explanation is, they don't do as advertised and neither would bring the venting up to code.

Most burner units, and you have two, have combustion air kits that can draw air directly from the outside.  There are also powered dampers which open and close as needed and prevent the burner from coming on if they fail.  Whether either of these could be used to solve the problem and meet the codes would need to be determined.

Again, this is my opinion and perhaps others will chime in with some code requirements, beyond my scope.

Bud

Picture of uncontrolled make-up air duct next to furnace.

 

Attachments:

Glad they used insulated duct for the fresh air intake ;)

Have you considered sectioning off the water heater and furnace from the rest of the laundry area? Make the that unconditioned space. How about a vent between the laundry area and the rest of the house effectively increasing the size of the laundry room and eliminating the need for make up air?

Be sure to check local codes before making a final choice. As Bud said this may be a HVAC contractors issue, although I probably wouldn't call the one that stuck in the 6" flex for fresh air...

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Tom Mallard replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
"Right, that reinforces my understanding of how it works, I was after what to plug in for values in…"
2 hours ago
Hal Skinner replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
"Products like these dont have an R-rating. You still have to have the R-rated insulation to meet…"
2 hours ago
Graham Irwin replied to Tom Conlon's discussion Whole House Fans - Love 'Em or Not?
"Thanks for the input. The next question to ask is "how much cooling power is delivered in each…"
3 hours ago
Brandon Walton commented on Brandon Walton's blog post 12 Things Every Home Performance Contractor Should Have on Their Work Truck
"Totally off topic William, but yeah could use a bit more I suppose "
3 hours ago
William H Nickerson commented on Brandon Walton's blog post 12 Things Every Home Performance Contractor Should Have on Their Work Truck
"One more thing...you need a little more bend in that cap"
4 hours ago
Tom Mallard replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
"Sounds like the perfect, thin insulator adding enough thermal inertia to separate two masses and/or…"
4 hours ago
Hal Skinner replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
"OK Tom, I think I am on the last questionow,,,I think.  LOL Going under the building and…"
6 hours ago
Hal Skinner replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
"Tom, sorry for having to break this up but my responses I guess are too long. You talking about the…"
6 hours ago
Hal Skinner replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
" "
8 hours ago
Hal Skinner replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
"I guess I got too mlong winded ther, it cut me off. 1.  Spray the coating on the ducts, plenum…"
8 hours ago
Kurt Shafer replied to Tom Conlon's discussion Whole House Fans - Love 'Em or Not?
"Jan, Here are some facts. the 30 inch fan from Home Depot (not one I would recommend) is rated at…"
8 hours ago
Hal Skinner replied to Hal Skinner's discussion Rooftop A/C units and exposed ductwork in the group Radiant Control Coatings
"Hi Tom. It looks like I will have to start off most of my answers to questions with this…"
9 hours ago

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service