Replies

1. 
   VaTom | Nov 10, 2006 03:38pm | #1

   Your air change system does not supply make-up air unless you positively pressurize the system, which the commercial units don't.  Not pressurizing means make-up air is brought in through leaks unless you plan for some make-up source. 

   I pressurized our house and occasionally run a woodstove with no outside air source.  We don't notice any difference in our 20k cu ft.  Same for the exhaust fans.  The other reason for pressurizing is making all leaks go out, with obvious benefit.  With a cast-in-place concrete house and fixed glass, we have few leaks.

   The tighter the house, the more important to pay attention to these details.  Congrats.

   PAHS Designer/Builder- Bury it!

2. 
   Tim | Nov 10, 2006 04:16pm | #2

   You can set up an ERV/ERU imbalanced somewhat. Do you have a forced air system? I use a Skuttle, which is a barometric damper, to allow outside air into the return side of my furnace, which runs on a ventilation (very low) speed constantly. When exhausts and other drafting appliance lower the pressure in the house the damper opens more. In normal operation, it maintains a slight positve pressure, when everything is closed up tight. 

1. 
   user-217211 | Nov 10, 2006 05:09pm | #3

   That's very interesting. In theory, an ingenious solution. Have you tested it to prove that it is working as intended? This is one of those systems that would be difficult to recognize when a failure occured. What is the max cfm range that you can expect with your setup? I would guess that it does nothing for the kitchen exhaust. Can it handle, as a for instance, two bath exhausts and a dryer at the same time and still maintain a positive pressure? How tight is your house? Lot's of questions, sorry.There is only one planet earth. How many chances do you think we get with her?

1. 
   Tim | Nov 10, 2006 08:24pm | #4

   Have I tested it? In terms of actually measuring differential pressure, no. I have sealed combustion appliances, and generally ventilate my bathrooms with a partially open window, unless its below zero. I have watched the damper work, gone and turned on every exhaust fan in the house and watched it slowly change to a more open position, and shut everything down and watch it go back to a "normal" position.

   My house has (2) 2x4 walls, the outer wall has no penetrations, unfaced fiberglass batts, full osb sheathing, a housewrap and fiber cement lap siding. There are approximately 100 windows/doors and three WBFP. The interior 2x4 wall has fiberglass batts, continuous vapor barrier on the interior side, 1/2 gwb with latex paint. All of the electrical and limited plumbing is contained within the interior wall. There is r50 + ? in attic spaces (R-35 batts between the trusses and an extra 12" to 18" blown over top of that), all plate penetrations are sealed. Continuous soffit and ridge vents, rafter baffles keep the roof vented in the truss areas. Every window is sealed to the sheathing/housewrap and extended jambs and/or trim are sealed via low exansion foam to both walls. I have a heating load of about 20 btuh/sf (at -15) and an air conditioning load of 1000 sf/ton (at 95).

   I did this work piece meal (room by room) and noticed as more and more was completed, it was getting harder to get a good draft going in the fireplace. That's when I installed the Skuttle. I have noticed a significant improvement with it installed. The good thing is, on a very simple basis, the device responds to any exhaust, kitchen, bath or dryer.

   The unit is a 6" damper, and can reasonalbly pass 100 to 120 cfm, given the short run of duct I have connceted to it. The volume of my house absorbs many short term transients, as it is very large (approximately 48,000 cubic feet) and as I mentioned before, even with all of the sealing, there are enough windows and doors that it cannot be considered "unusually tight". Can it handle multiple exhausts and a dryer venting and maintain a positive pressure? No, not for an extended period of time.

1. 
   user-217211 | Nov 11, 2006 02:51pm | #5

   Thanks for your reply. I think it's a very interesting system. Congratulations on your house. It sounds like you've worked very hard. What do you use for your fireplace makeup air? What is your trade?

    

   There is only one planet earth. How many chances do you think we get with her?

   Edited 11/11/2006 6:53 am by Ray Moore

1. 
   Tim | Nov 13, 2006 06:35pm | #7

   The fireplace I use daily has direct makeup from outside.

   I am a Mechanical Engineer, specifically involved in HVAC systems, controls and equipment design/specification as well as system/building problem investigation and remediation.

2. 
   user-217211 | Nov 13, 2006 09:40pm | #8

   I thought so. It sounds like you have a good handle on all these issues.There is only one planet earth. How many chances do you think we get with her?

3. 
   Brian | Nov 11, 2006 04:35pm | #6

   I built our house with ICFs - its very "tight"

   We ran 4" pvc under the footers (from the windward side of the house) to where the masonry heater will be (terminating inside the firebox) for makeup air.  You could do something similar, and add a damper.

   We have a 625 cfm blower over a commercial range - its low tech, but we crack open the nearest window when we use it.

   We also open windows in the bathrooms when necessary - no vents.

   An ERV won't help (unless you pressurize, like VATom) but I'll bet someone makes a bathroom vent that brings in make up air.

    

   Treat every person you meet like you will know them the rest of your life - you just might!