Replies

1. 
   IdahoDon | Apr 21, 2012 12:43pm | #1

   It's a great idea to insulate the furnace room if you have a makeup air vent.   I wonder if 8" is enough for both a gas furnace and water heater going at the same time.

2. 
   MarkH | Apr 21, 2012 04:46pm | #2

   I would consider getting a condensing furnace that uses a pipe to bring in combustion air.  It may allow you to close off the vent.  Of course it should reduce fuel usage also.  I went straight from a coal gravity furnace (with natural gas conversion) to a cndensing furnace.  Talk about improved efficiency!

3. 
   DanH | Apr 21, 2012 09:02pm | #3

   If your furnace room encloses the furnace even halfway tightly then the air from the makeup air duct will flow directly into the furnace and water heater without much "coaching".  It's definitely worth it to do the insulation and air sealing of the rest of the basement, and to do whatever you can reasonably do seal the utility area from the rest.

   There are assorted damper arrangements for makeup air (and flues), but they're problematical, since they often put you in conflict with code, and they can be unreliable.

4. 
   rdesigns | Apr 23, 2012 09:47am | #4

   By "makeup air", I assume you

   By "makeup air", I assume you mean air for supporting combustion of the furnace and WH, and, if so, it is needed and code-required. 

   Isolating the furnace room and insulating and air-sealing the rest of the basement is a very good idea, and will save energy dollars along with making your house more comfortable.

   When you have finished, do a simple air-balance test that will be very important, first for safety, as well as for energy savings:

   After closing all windows and doors, set your thermostat to "FAN ON", then go into the furnace room and shut the door. Then feel under the door to see if air is rushing into the furnace room. If it is, you have the potential for dangerous backdrafting of the WH due to the furnace room being de-pressurized, which will also have the effect of drawing too much combustion air  into the furnace room and being distributed throughout the house by the duct system.

   In that case, you may need an experienced HVAC contractor to find and correct the problem.

5. 
   Mpls1921 | Apr 25, 2012 10:38pm | #5

   Thanks for the replies! 

   The 8" was a WAG, it's probably bigger than that.

   The furnace room does not at all tightly enclose the furnace/water heater area.  That room is probably 25% of the size of my basement.  Isolating it would be problematic, as there is all kinds of retrofited forced air HVAC/electical/pluming all over the place.

   I will probably insulate the walls with an inch or two of foil faced (so I don't have to cover it with drywall) poly-iso, and foam the rim joist.  I would love to just cut up some XPS for the rim joist, but there is cement in every bay sloped from probably 1" thick at the top to the full width of the foundation at the bottom.  I'll see how hard it is to remove, but if it's not easy, I'm calling a Icynenne installer to spray a couple inches on it.

   Thanks!

6. 
   Clewless1 | May 10, 2012 08:17am | #6

   Yes, insulate the duct. A damper is a great idea, too. Make sure it is a tight fit. Also make sure you chat w/ the BO about it. In concept, the damper is simple and easy. But as someone else pointed out ... also a code issue. Commercial boiler rooms often have such a damper in them. However, they are tied to the combustion device and MUST be open before the unit can fire. This is done w/ a 'make' switch. This is a switch that ONLY closes when the damper reaches the full open position. It's a simple device, really. That would have to be tied to your combustion devices (furnace/water heater). 

   You should isolate your mech. room. Seal it ... I know you've got a lot going on ... which means you also have a lot of 'leakage' going on.