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: 253

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.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Mark posted events
9 minutes ago
Colin Genge posted an event

Air Leakage Testing for Home Inspectors at Online

July 7, 2015 from 1pm to 2pm
• What sort of effect will IECC adoption have on the building industry? Home owners? Inspectors? •…See More
1 hour ago
jerrycarter is now a member of Home Energy Pros
2 hours ago
Bijou Lulla posted a blog post

ENERGY EFFICIENCY RETROFITS.....IN NUMBERS WE TRUST

There has been much ado about the recent paper published by E2e; Do Energy Efficiency Investments…See More
16 hours ago
Mariusz Chorazy posted a blog post

Here are a few tips to keep your air conditioning bill low

TAKE GOOD CARE OF YOUR AIR CONDITIONER – Like any major appliance, your AC requires regular…See More
yesterday
Dale Pickard replied to Rod Fox's discussion Does altitude affect AFUE? or just the input/output BTUs?
"Morgan, I got this below from the Knight installation manual. I note a few things, -These…"
yesterday
Dale Pickard replied to Rod Fox's discussion Does altitude affect AFUE? or just the input/output BTUs?
"Hans, The car manufacturer's are doing it with mass flow sensors and oxygen sensors…"
Saturday
Dale Pickard replied to Rod Fox's discussion Does altitude affect AFUE? or just the input/output BTUs?
"I was trying to avoid naming manufacturers, but I was going by the published information for the…"
Saturday

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service