On Mon, 26 Nov 2007 12:47:33 -0800 (PST),
wrote:



PaPaPeng wrote:
On Mon, 26 Nov 2007 10:38:47 -0800 (PST),
wrote:

Walls are R11 with an extra inch of styrofoam and
housewrap under the siding.

That's your problem. The walls should be R30. The insulation
effectiveness (ie reducing heat loss) graph plot rises steeply from
zero to R30 then flattens off. That is beyond R30 you won't realise
much more insulation gain. But R 11 is certainly pretty low on
insulation effectiveness.

So if I put more insulation in my walls, the furnace will stop blowing
cool air? That doesn't make sense.


I am not so sure about the explanation for you furnace not blowing
hotter air. It sounds like there is a large mass of colder air in the
house and it takes all of the 30 minutes to warm it up to the set
temperature. Most of that air is recirculated air drawn from the
rooms back into the furnace. Someone knowledgeable will have to see
the furnace running to troubleshoot. It can be you. Put a
thermometer in the hot air plenum, more thermometers some distance
away in the main trunk and see what the readings are. That should
provide a clue.

I don't have the answer for the furnace. On insulation try asking
your city hall agency that deals with home construction permits and
ask how it can be done in your location. Its just that when I built
my house (1980, sweat equity program for people on limited income)
that was what the construction class instructor told me. It sounds
like yours is an older house (80 yrs?) when such things were not well
understood or insulation was absent altogether. Some of these older
houses had insulation added as an afterthought and the studs weren't
deep enough to put in thicker insulation. Insulation batts have to be
loose to trap air pockets. Squeezing R30 batts and compressing them
into a thinner wall space is ineffective.

Effective insulation means that less heat will be lost through the
walls by conduction. Sealing the gaps around the doors, windows,
electrical boxes, etc. will reduce heat loss by convection (ie
escaping warm air and letting in cold air).