Imagine all the added elbow room if the adjoining water heater was GONE during
a furnace retrofit. Well, that's what I'm going to be doing (See Downsize
little less than two weeks.
My contractor wants to DOWNSIZE to 75k from the 100k size of my 14-year-old,
conventional (spec) gas furnace. Of course, this will be done with a "90" (or
better) model. He claims that the improved efficiency of the new furnace will
compensate for the difference. Do you agree?
He also mentioned, after taking measurements TWICE, that I need an
18-inch-frame unit and that a bigger unit would require a reducing "boot",
which he represents as a compromise. What's with that?
Then there's the PVC vent(s) outside. He claims that it is legit to use only
ONE - an exhaust line - that the furnace uses INTERIOR air for combustion. He
represents this as a DESIRABLE way to EXCHANGE interior air with fresh.
I am old enough that this furnace may well be part a big part of the resale
value of our home. He wants to install a "Weathermaker" furnace and a Rheem
ac condensing unit outside. He says that the Weathermaker FURNACE is
virtually the same unit as a Rheem so this would be an up-front cost-saving
issue ONLY, assuming he's right. What about resale then?
He further says that the condensing units are different and therefore,
recommends a Rheem unit outside.
I would get at least 3 and preferably 5 estimates and quotes, then
did he measure you entire home and do a heat loss calculation??
since he advocated downsizing the hot water tank I would question his
you better off using outside air for combustion, old houses already
exchange air enough and besides certain home chemicals have caused
furnace heat exchanger failures in the past. everything I have seen
says outside cold air, is more dense and better.
how long has he been in business? buy a furnace ONLY with a lifetime
heat exchanger warranty and at least 10 year parts and labor for
are you buying a 2 speed furnace? they run on low speed in moderate
temps, then step up for more demanding situations like zero days.
slightly more expensive, but selling point if your moving
Matching the CFM capacity of the ducts to the new furnace is more important
than a heat loss calculation. In some cases, drawing combustion air from
inside is preferable. Large amounts of some chemicals can ruin a heat
exchanger, but most people don't have that situation.
Something along this line was pointed out to me recently. You have a
limited lifetime warranty on the HX in your furnace. After some time, the
manufacturer is going to stop making replacement parts for that furnace.
Besides, look at the Lennox Pulse furnace. They started going bad and
Lennox would give you a pittance towards a new Lennox furnace. No other
brand, just Lennox.
Go with what your contractor says, it sounds like he knows what he's doing.
Rheem lets you use just an exhaust. They also let you downsize the last 18"
from 2" to 1-1/2" PVC in certain instances.
If you put in the bigger unit, the blower will produce more CFM, and
velocity of air out the ducts will most likely be offensive. Rheem Mfg.
bought out Weathermaker years ago. They might even be the same color now. No
buyer is going to notice that they both don't have the same name. I sell
Ruud because my wholesaler stocks that in my area. When they can't get a
matching unit, they go to other parts of the country for a Rheem.
Unless you get a written load calculation you will never know the truth.
Oversizing was and is common. I had 110000 btu, now I have 47000, on low
fire and on the coldest days I only run 12-14 hours. So I am still
oversized. If your unit is 80% efficient and you up efficiency to a 94%,
you can downsize 18% and get the same heat output. But nobody here kmows
how he is comming to that conclusion. Get several estimates, there is
alot to choose from.
No one here can agree or disagree without doing measurements and
calculations for heat loss. You did not say how your contractor determined
you should downsize.
My guess is he is right, and did the calculations but I don't know.
While I would tend to put in a intake for outside air, with a higher
efficiency unit, your home is old enough (at least 14 years) to be loose
enough not to "need" it's own inlet.
I didn't comment on the WH thread, but again, look at resale. If you go
back with a tank type unit and you'll be selling soon, will the smaller one
fill the whirlpool tub for the new owner? For the 20-25 dollars difference
between the 40 and the 50, I'd go with the fifty. I have seen home
inspection reports that comment on the size of the WH not being enough to
fill the tub.
Yes and no.
Simply called a transition. Furnaces come in 3 basic widths, 21", 17" and
That depends. I use OA for any 90% furnace that is in living space
(basement or closet installation). Some attics get it, but very few
Most people out there look at the age of the furnace, not the brand. The
one concern would be a matched system to get the proper efficiency for the
As long as it's a ARI match, that's fine. Rheem has scroll compressors and
WK still uses recips. Scrolls will last longer.
Ratings are based on input. Assuming a 100,000 Btu unit of 80% efficiency,
20,000 is going up the flue, not into your house. With a 100,000 Btu unit
of 90%, only 10,000 is going away, so you have an extra 10,000 going to heat
your house. Thus, a reduction in capacity will give the same amount of
Other factors can come into play, this is meant as an example, not exact
calculations or your system.
Is that true?????
I thought furnace ratings were based on OUTPUT...i.e
a 100,000 BTU/Hr 90% furnace DELIVERS 100,000 BTU per hour.
and a 100,000 BTU/Hr 70% furncae also delivers 100,000 BTU/Hr but takes
more fuel to do it.
My York (warm air oil fired) furnace nameplate says Bonnet BTU 100,000 which I thought refers to the output not the input.
Im seeing lots of crap in your post Jim.
Downsizing a water heater and furnace may be good or needed but it
shouldnt be done as a guess. You need to have a Manual J load
calculation done to get the heating and cooling selected.
You water heater also needs to be sized properly,....venting included.
You could be making a very costly error if someone is guessing.
Reducing boot? More crap. A properly sized unit and correctly sized
ductwork. Plain and simple.
One PVC exhaust pipe? While legit, its also the lazy way. You will
lose some efficiency by burning already heated indoor air and your
heat exchanger will be compromised over time by burning indoor air
filled with chlorine (bleach) fumes, paint, aerosols and other
contaminates. Its your money though................
Exchanging air? NO, the furnace venting is not meant for that. An ERV
or HRV is meant for that.
Resale of your home? NO, you will not get back what you paid for the
system when you sell your home. People look at a home and usually dont
even pay attention to the hvac system unless a home inspection says,
"The furnace is 27 yrs old and will probably need replacing in the
Now, whats up with the two different brands of the furnace and A/C?
Are you talking Weathermaker, WeatherKing, Carrier, or Rheem?
I would advise getting a matched system if you are replacing both
pieces and get a cooling coil with an expansion valve, NOT a piston or
cap tube metering device. Get at least a 5yr or 10yr PARTS & LABOR
warranty depending on how long you will be in your home. It will pay
for itself in one major repair. DONT be confused by the included 5 yr
parts only warranty.
Dont go cheap. Its really just not worth it unless you plan on moving
Just credit my PayPal account :-)
Unless the contractor provided the manual calculations or you have added a
bunch of insulation improvements since the orginal install, I would be
Do you heat more than cool?
Efficiency is not BTU's, efficiency might help the consumption but not the
heating load back to BTU's again.
The boot may be changing the duct from one size to another. I call it a
transition. Very common and I can not see the installation. A good
sheetmetal man can make a round funnel with a square hole.
The UPC, or uniform plumbing code in my area does reconize using inside air
for combustion. But since your heating why would you do that. All of the
combustion air is heated and must be replaced by,,,,,,,,,,,, cold air.
Most new gas appliances have charts for the combustion air sizes.
Sounds lazy to me.,,,,,,, again I can not see the installation.
Resale is what the buyer will pay. Sheetmetal and a pretty sticker are just
that. Most buyers are just begining to think about operting costs. Higher
effency, and higher SEER may help the resale, New installs after 1 Jan 2006
are to be SEER 13 min. SEER is a cooling rating and has not a damn thing to
do with heating. Heating is a COP number.
I have not a clue what you or he means by this.
Like the others have said, more contractors, more quotes before you decide.
He could be correct. I'm looking at replacing the 1979 furnace in my house
which is a 125000 BTU and current size estimates say I should have a 75,000
BTU so it appears mine was was oversized. How often does yours run now and
for how long, too large will short cycle.
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