We recently purchased an brand new home in August and this is our
first year in the house. The house is much larger then my previous
house (3200 sqft vs 2400 sqft) and I've noticed that the furnace runs
much longer and much more often then my previous house. Based on the
specs of the builder, they put in R-11 batts in the ceiling with R-27
blow in "for tight insulation" and R-13 batts in the walls.
Does this sound sufficient? I'm not sure what the total R value would
be for the ceiling (do you add the R-11 and R-27 to come up with
This past weekend, it was approx 0 degrees out. I turned the furnace
down to 62 before we left for a day trip. When I returned, I set the
furnace back to 68 (where I normally keep it) and it took approx 2.5
hours for the house to heat from 62 to 68. This seems very excessive
I've read the following online: "A properly-sized system is designed
as closely as possible to the needs of the house; on the coldest days
of the year, it should run almost continuously."
Bull. I live north of Chicago and it takes about 1/2 hour to get the
house from 62
to 67. In fact it does it every day. My furnace goes off at 8am and
doesn't turn on till
3pm every day. The lowest the temp gets is 60 deg and thats when it's
10 below outside.
It sounds like your system is too small for the house. It wouldn't
hurt to contact the
building department with these questions.
Another thing is that no matter what the wrapper says, the quality of
the insulation depends a lot on the quality of the installation.
Also, if you have crappy air sealing, that isn't going to help
either. I think that unless you live in a place that is 70 degrees
year round, you should have r 21 in your walls, but that's just my
well new high efficeny furnaces are sized closely to the home, for
most efficent operation. but gone are the days you could raise the
temp of the home from 50 to 70 in a hour. new furnaces just arent that
on insulation the higher the R value the better.
ideally the builder would of used closed cell foam, its costly but its
over R6 per inch.
of course you would of had to pay the added cost, and since its not a
see me item like granite countertops, its harder to justify.........
minimum R standards for ew homes should be raised
With your huge house and perhaps cathedral ceilings, great room (high
ceiling) and all the other popular things now found in new homes, you
probably have lousy air circulation and a sadly undersized furnace.
IMO you need to get some competent help to analyze and correct the
problem. Be ready for a shock when you get the quotes for the work.
I have the builder and the HVAC guy coming on Friday to see what's
going on. You mention "competent" help to analyze and correct the
problem. Who would I turn for this? Should I not trust the opinion
of the HVAC guy and the builder?
Come on now, these are not the guys that caused the problem. Are you
going to let them brain wash you into believing that the situation is
normal? Whoever designed the house is the cause of the poor
performance. Get a decent architect on board, someone familiar with
ALL aspects of residential design. If you are near a major university
with such a department, ask if someone there can recommend a firm in
your area. Browse the Yellow Pages. Knowledge is power. Good luck.
I am just north of you, in WI, and R38 (which you have) is code for
ceilings, and I think R13 is still ok for the walls. Hard to expect a
builder to go beyond the minimum standard.
I'm not too surprised that, with the extreme temps, it took a long
time for the furnace to get up to temperature. The furnace should be
sized to keep up with the heat loss on the coldest days.
It may all be normal, proper sizing of a furnace is that it runs
nearly continously at the coldest day which is about -20f in chgo. 2.5
hrs is not much seeing all the furniture and walls you must heat that
are now cold. Oversizing a furnace leads to short cycling and
uncomfortable heat. is it a 2 stage unit, you might check that the
second stage works. You have R38 , or at least you think you did, as
nobody cheats, and blown in settles more than batt, Measure it
yourself and calculate R value. But what you have is code, its the
minimum, not optimal, and the code is old based upon cheap gas so do
your own research. Optimal some say R 60 some say more. Im sure a laod
calculation was done and you should have looked into projected heating
costs, and they might be normal, depending on your design.
I posted a comment like yours above ("but the most efficent furnace is
one that runs continiously on the coldest days") and others laughed
My buddy is a construction super intendent for a big builder in the
area and they sell houses that are similiar and size and he said that
they usually have 2 furnaces in a house like mine. There is no doubt
that I would love to have a seperate furnace for the 2nd floor.
Another question... this same buddy says that they do one single duct
run to the attic and then branch it off from there to the individual
rooms with the registers on the ceilings (2nd floor). Mine has
individual duct runs with individual dampers in the basement for each
room on the 2nd floor. Which setup is better? I would assume
individual runs would be better since its not going to a cold attic,
but he thought my setup was strange. Adding a 2nd furnace will be
more of a headache with my setup (I would assume).
being a construction superindent means he is hopefully a expert at
building stuff. he follows plans.
he doesnt design building and probably isnt a HVAC expert either.
Thoise 90%+ efficent furnaces are rated like that during continious
operation. thats the coldest day of the year.
on a 50 degree day in a area that typically sees zero degrees the 90+
furnace isnt near its top efficency.
the basement feed furnace ducts are more efficent than top feed.
with top feed the hot air must be pushed up all the way to the attic,
and back down again to floor level.
with basement feed hot air is still pushed, but natural convention hot
air rises cold air falls helps a lot. more efficent less electric
blower power needed, less ductwork needed.
down feed is used for open floor plans and appearance but its less
the reason constant operation is more efficent? the furnace transmits
all the heat it produces into the air. in a cycling situation much
heat never gets moved to where you need it, on first heating things up
before blower turns on, and afterward, when hotr heat exchanger is
left to cool.
have you noiticed high efficency furnaces tend to blow cooler air on
start up? thats a attempt to minimize heat lost during start up...
note the dual speed furnaces are another attempt to address these
the idea is in less than full heat needs run the furnace at less than
full btus continiously, this minimizes losses
In a cold area like yours, you should have thermal break insulation in
the walls, and at least R-19. R-38 in the attic is absolute minimum.
Your furnace should respond quicker if it's only 0 degrees. It will
probably be inadequate during really cold weather, which will sometimes
You might think about paying for an energy audit. It's pretty common
for plumbers and electricians to rip up insulation and not replace it.
You may have some gaping holes in your envelope. If you discover any,
see if the home builder is a member of his association's home warranty
program. You may be able to get it fixed with minimal cost to you.
For email, replace firstnamelastinitial
with my first name and last initial.
It is true that for best efficiency, the furnace should be sized so
that it is just able to keep up on the coldest days. An oversized
furnace that cycles frequently will waste energy. Let people laugh if
they want, they can laugh all the way to the bank (to get more money
out to pay their gas bill). That being said, as you have noticed, a
smaller furnace can take a long time to heat the house up; 2.5 hours
seems like too long to wait for a standard thermostat set-back. The
poster that asked about whether the second stage is working might be
on to something; something for the HVAC guy to check out. Have the
house nice and cold when he shows up. If you just want/need a bigger
furnace you might be able to cut a deal with the builder on that.
Chicago has weather records going back well over 100 years and the
coldest it has ever been was -27 Fahrenheit. So if the system is good
down to -20 or so that should suffice.
Your insulation is the modern standard practice. Arguably there
should be more but at this point it is hard to add it anywhere but the
attic, where you could just have more blown in. There are lots of old
houses in Chicagoland with NO insulation in the walls - at least
you're better off than they are!
Fair enough, here are some references:
(canada mortgage and housing corporation technical bulletin)
http://www.alpinehomeair.com/Furnace-choosingsize.cfm (home heating
and it's not just efficiency, but also early failure of the unit is a
possibility. -- H
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