Excuse me, but you've obviously got me confused with HomeGuy. He's
guy that started the Win98 crap that got the thread off track and made
above quoted statement. Perhaps you remember him as the profanity
poster you previously engaged with.
Anyone who buys a new furnace and ends up needing to rely on any sort of
corrosion warranty will lose.
Because as past history has shown, you need to launch a class-action law
suit in order to ever get compensation.
If you think at the outset that you're buying a piece-of-shit furnace
that's going to break down on you like that, then it doesn't matter
whether or not you've modded the furnace. You shouldn't be buying a
piece-of-shit furnace in the first place.
On Dec 3, 1:46 pm, email@example.com wrote:
I didnt know furnaces ran windows. Consumer Reports mag did a poll of
about 22000 people years ago, the top results were suprising, you do
have CR mag online, right. If I was looking for one it would be
stainless steel heat exchanger not treated steel. If you over heat
them ive heard they fail fast. Checking the temp just above the
exchanger is something you should have set up and do. If it gets humid
inside when temps are mild, to mild for normal AC, a Vsdc blower will
do alot by running real slow and cycling the Ac only for humidity
removal, if its set up right. Vsdc should also save you 15-30% on
electric usage overall. The first generation untis failed within 6-10
years, ive heard but they redisigned the electronics so maybe they
last now, you still need the longest warranty if you go with the fancy
stuff. 10yrs is common and maybe 15yr warrantys are done now. 2 stage
or modulating gas valves allow more even heat. With a high efficiency
condensing unit you automaticly cut the size of overall btus needed by
10 to maybe even 15%. If you dont run it 24 hrs a day on the coldest
days you might cut its size more. But if you do the setback or
vacation alot recovery is harder. You could Diy it , save money, have
no warranty and maybe be covered on savings. I think vsdc motor is
600, but im guessing on all numbers.
I checked there already. They said the problem reports were about the
for all the manufacturers and didn't rate one better than the other.
some average price of a furnace information for the manufacturers.
not sure what that even means. Does it mean that the price for a
furnace from each company? Or does it mean that it's the average
the systems each company sells? If it's the latter, it's useless,
company A could offer more high-end systems and have a higher average
price, while actually being cheaper on the particular system type I
Thanks again for the help in the past on that CR stuff. I finally
got a subscription.
I was thinking about that. With the current furnace, with an outside
about 28F, it raises the temp from 60 to 70 at about 5F per hour.
26 year old furnace is 150K input. So, I'm thinking with 93% or so
new one, 100K should be about the same. It's not close to running
on the coldest days here in coastal NJ, which would be about 8F. But
any smaller and it cuts
back the ability to set it back at night. Right now it's set to go
to 60 at 11PM,
back to 67 at 5:30AM
I also take maybe 7 trips in the winter where I set it back to 50 and
from the above,
you can tell it takes several hours to get back to a reasonable
I've though about getting an thermostat that I could control via the
to set it back up when I'm on the way back.
Would you think it a good idea to go with a smaller one if it means
to set it back, even on a daily basis?
As far as the VSDC, etc., I'm going to see what the contractors have
in the systems
that meet the credit reqts as well as those just below it. I'm
thinking I'll probably wind
up essentially getting a better furnace for free when you factor in
On Dec 5, 11:08 am, firstname.lastname@example.org wrote:
The CR survey was notable because it stated Goodman to be less
reliable, but I guess you are not looking at Goodman.
Your 150k furnace is likely 82% and 123,000 output, a 100k 94% unit is
94,000 output so its alot less, near 30%. I wonder does it even run in
6 hrs at night on 6f cutback? a load calculation is really needed to
know what is needed, or just dont go to much smaller. The only real
need I can see for 2 stage or modulating gas valves is if you have
uneven heat and need more comfort. Just cutting my furnace size 50%
gave me more even heat but I was way oversized. Ecm-Vsdc would help
more in winter if heat is uneven but it really makes sense for AC if
alot of your climate is near 70 but humid or you need to boost AC.
With 7 trips a winter and setbacks you will be colder longer if its
alot smaller. I think the main benefit is a cheaper unit, but you
didnt say heat was uneven or bad. if your fine now maybe Condensing
and no fancy stuff is best. a bit smaller and heat will be more even.
I was thinking the current 26 year old furnace is more like 60 or 65%%
you think 82% is way high? I'd expect that from a more modern
the current low cost entry level systems, but not from my ancient
beast. If it's 65%,
then replacing it with a 100K, 93% one is pretty close.
I set it back to 60 at 11PM and it definitely will run overnight if
it's cold weather, probably
from the low 20s on down.
The first contractor, Carrier guy is coming tomorrow and I think he's
going to do one. But it
would seem to me that the actual experience I have with the current
one is just as useful,
maybe more so. At least for the heating part.
That's about where I'm headed. The only issue I have now is that it
good to have more cooling upstairs. Main issue there is the limited
originally installed. One thing I want to look into is more blower
help with that. But I think the best solution would be a second AC
upstairs. I don't think it's enough of an issue though to warrant
So, I'm thinking get more airflow if possible, and a system that's
sufficient in rating
to meet the tax credit.
On Dec 5, 1:35 pm, email@example.com wrote:
I know boilers have been 82% steady state running for over 110 years,
My 1954 Kewanee steam 1.200,000 Btu is 82% running and a 110 yr old
style or older, for boilers the reduced water supply is the main
advantage today, for steam they are now still only 82% rated. Better
controls, flue damper, electronic ignition and holding less water are
steam boilers only improvements. For furnaces with the tank style
exchanger I think those are less but if its clean, not way oversized,
not short cycling, if the burners are burning right 82% is my guess.
1984 isnt that long ago, we went through a energy mess in the mid 70s
and I was converting to flourescents as utility prices were going
up.Google a bit and see if you can find out what things really were 26
years ago. Your payback might be alot less than you think with a new
Don't joke. Next year they'll be running linux or android.
So post them here.
Yes. Stainless for both the primary and secondary exchangers. Take a
magnet with you to the hvac dealer's show room and test the units they
have on display.
Correct term for vsdc motors is ECM. ECM motors are a crock of shit.
Best you'll save is 100 watts compared to 1/4 hp AC motor, and less if
you have 2-speed AC motor. Saving 100 watts at 10 cents/kwh is about
$100 (that's 100 watts continuously for an entire year). Now subtract
the electricity used by the furnace motherboard, and various other
blowers and condensate pump. The extra 100 watts used by AC motors are
dumped into the house as heat - which is what you need in the winter
(and spring and fall depending where you live) so it's not all wasted
Lifespan of ECM motor is 1/2 to 1/4 that of AC motor, and it's 4 to 8
times more expensive (upfront cost of furnace is higher, repair costs
higher). ECM motors create EM/RFI on your household wiring, can
interfere with tv and radio reception.
Now tell me how you're saving with an ECM motor.
So where are we?
1) Adding second stage heat exchanger to conventional (70 - 80%)
furnaces from 30 years ago gives us condensing furnace (95% give or
take) - which is good. I do like that improvement.
2) Using cheap steel for heat exchangers compared to furnaces from 30
years ago is bad. Using stainless is good.
3) Using electronic ignition is bad comprimize from cost/savings point
of view compared to standing pilot light. No real need to use
electronic ignition in modern condensing furnace.
4) Using ECM motors is also bad comprimize compared to 1/4 or 1/3 hp AC
squirrel cage motor. *Actual* or *Net* energy savings don't justify
extra cost and reduced longevity.
As a consumer, give me the choice of electronic ignition or conventional
pilot. Give me the choice of ECM vs standard AC motor. Give me the
choice of mechanical thermostat (in the furnace) to control gas valve
and fan motor instead of electronic motherboard. Give me all stainless
for the exchangers. If you don't give me ALL those choices, then I say
that modern furnaces and the entire industry is a crock of shit.
Beyond the furnace itself, it's time to start ducting winter heat around
the AC coils instead of going through them. You want efficiency? It's
not efficient to blow air through coils when you don't need to do it
during the winter.
It's also time to allow for spring/fall cooling by having ducting and
gating that allows the furnace to pull return air from the outside,
force it into the house, and gate the interior return air back to the
outside. When ever you want the house cooler, and the outside air is
cooler than the inside air, then why use your AC when you can draw
outside air into the house directly?
I dont know how to cut and paste yet but its 2008 CR magazine furnace
Ecm Vsdc, it can run at 100watts vs 375 for my 1/4hp, thats near 70%
saving in slow mode, maybe near 100w less at high speed.
Who in the US pays only 0.10c per Kwh, you must live near a big Dam
and get subsidised electric because im .18 and so is the rest of the
US, many place are near 0.25 kwh.
You miss the point, its comfort or else you wouldnt even have a
heating system. Vsdc can remove in low speed maybe 50% more moisture
with minimal cooling so its great in humid areas, great for homes with
uneven heat. It is about comfort, but can save the cost of the motor
in electric usage over 6-7 years. That was my figure years ago at .
You have to know yearly hours run in heat and AC and a real Kwh cost
to make any claim to it not paying back.
Lifespan, are you refering to the old or new redesign motor.
Electronic ignitions failing, so do thermocuples.
How exactly do you improperly install a furnace?
If you are replacing an existing furnace, one that has been running for
years in a given house and presumably giving satisfactory service, then
how possible can you remove it and "improperly" install a new one in
What is meant by improper? That a water line is connected to the gas
input line? That the upstairs thermostat is connected to the furnace AC
power input? That the return duct and output air plenum are connected
How does the correct sizing of a furnace impact on whether or not the
heat exchanger lifespan is impacted by being stainless steel or regular
Would these be the same ductwork designed and installed by licensed
Would these be the same ductwork that was original to the homes in
question - the same ductwork that somehow didn't manage to dammage or
burn out the motor in the previous furnace - presumably an AC motor?
I'm sorry, but if my 36 year-old AC motor didn't burn out because of the
size of my existing ductwork, then it's a crock of shit that the same
ductwork is the reason why a new ECM motor burns up.
Blame the ductwork. When you have to explain to the customer why his
new $4000 furnace is costing so much repair hassles, blame the ductwork.
You need to show you're a man by pointing out exactly which of my
statements above are wrong.
I'm right when I say that:
1) ECM motor uses 100 less watts when running full speed compared to 1/4
hp AC motor running at full speed.
2) The extra 100 watts used by AC motor is dumped into the house as heat
during the heating months, so it isin't exactly wasted energy from the
point of view of the home owner.
3) You can't compare the energy usage of an ECM motor running 1/4 or 1/2
speed against a single-speed AC motor. If you want to compare the costs
of multi-speed operation, then you must compare ECM with a 2-speed AC
motor, and you must correctly estimate the amount of time (total hours
per year) that the fan will be running at fractional speed.
Totally wrong, because you have to factor in the control or drive
electronics that's powering the motor, and when you do, you'll end up
with burned out transistors.
The efficiency of fractional horse-power ECM motors are (at best) 60%,
while a 1/4 hp PSC AC motor will have an efficiency of 40% (if running
at full speed). 1/4 horse power is about 186 watts, so an AC motor will
use about 465 watts, while an ECM motor will use 310 watts. The
difference (about 155 watts) would use 1,357 kw hours given a
continuous 1-year run time. If the total electricity cost was 15 cents
per kw hour, then that equates to $200 per year.
Now if you consider the case of a 2-speed AC motor compared with a
2-speed (or even variable-speed ECM furnace) and if you factor in that
in a typical use-case that neither motor would or could be operating for
up to 25% of the time, then the potential savings from using an ECM
motor will almost certainly drop to closer to $100 per year.
Now if you factor in that the 155 watts of extra energy being used by
the AC motor is given back to the house as heat, then you need to
determine what that equates to in terms of cubic-feet of equivalent
natural gas and subtract the cost of that amout of natural gas from your
electricty bill to get the true additional electric cost by using an AC
motor instead of an ECM motor.
While all ECM motors are capable of infinitely variable speed and can be
implimented as such by something as cheap and easy as programming code
in the controller, furnace makers charge a fortune for anything more
than simple 2-speed operation. That is another crock of shit for this
I could argue that a belt-driven fan with an AC motor with bushings is
quieter than a direct-drive ECM motor with ball bearings.
Or so you think. There's no way that a home-owner (or even consumer
reports) is going to know which units put out RFI, and which units
actually give you what you pay for. Models change all the time - too
fast for independant testing and analysis to have any effect or be
useful for the buying public.
Which equates to 155 watts as I calculated above.
Be a man and tell me where I've said anything wrong.
We're comparing 30 - 40 year-old furnace technology with conventional
furnaces. If furnaces cost proportionately more today in terms of % of
disposable income then I should expect no less durability or longevity
compared to the older furnaces. You seem to be an appologist for the
industry by indicating that we should pay more and expect less.
Because standing pilot lights have been used for decades and have proven
themselves to be reliable, safe, simple, and cheap.
The pilot light and it's thermocouple switch have proven to be an
excellent design in terms of safety, reliability and durability for
residential furnaces. Do you disagree? Do you have the balls to
Removing the electronic ignition and replacing it with a pilot-light and
thermocouple does not constitute "removing a safety" device. Get a grip
See above. Best case savings is $200 a year, typical savings will
almost certainly be less than $100 a year.
Anyone who lives in a climate zone where they expect to use their
furnace at least 5 months out of the year will realize less than $100
savings in their combined electric and gas bill just by having a furnace
with an ECM motor. Anyone who lives in a more temperate climate zone
and runs their fan more often either alone or in conjunction with their
A/C unit will come closer to the $200 in electricity savings.
We're talking simply about ECM motors replacing conventional PSC AC fan
motors in residential furnaces. Motors that are part of other
components (heat pumps, A/C compressors, dishwashers, clothes washers,
dryers, etc) are another matter and have different cost/benefit
The single largest decrease in my energy bill that the furnace industry
can give me compared to what I have now comes from the 2-stage
condensing heat exchanger. Better airflow design, thinner materials,
stainless, possibly better burner design, etc. All of that comes from
better thermodynamics and materials - NOT ELECTRONICS.
The addition of electronics - particularly the electronic ignition and
ECM fan motor, adds unnecessary cost and complication to the modern
furnace with no tangible benefit to the home-owner and comes with
additional medium to long-term cost of ownership costs and device
down-time caused by component failure.
Screw the contractor. I want a box that will sit there and work year
after year. It's no consolation to me that a repair tech is just a
phone call away. I'll take reliability and durability any day over
repairability. Especially when it comes with lower up-front costs (no
electronics). And in this case, I'm not even sacrificing
repairability. Low tech = high repairability.
I can install myself any furnace. That's not the point. I'm just
bitching about they choices that furnace makers are making when they
design / build them.
When you have electronic ignition, you HAVE TO HAVE an array of
electronic sensors to make it safe. Having those sensors and
electronics comes with a price - a hit to cost, durability, reliability.
When you have a standing pilot light with electro-mechanical
thermocouple and gas valve, you don't need sensors or electronics,
because it's inherently safe.
We're not talking about the thermost here. I can have the most
advanced, computer-controlled thermostat I want upstairs to control my
35 year-old furnace, yet still have no electronics *in* my furnace.
Understand the difference?
By having too high of a TESP (total external static pressure.
Older furnaces had a lower CFM rating, hence they have a higher temp rise
for a given output BTU rating. Newer equipment for effeciency's sake have
thinner heat exchangers (less metal thickness to push the heat through) that
can't tolerate the heat without cracking hence they have a higher CFM
rating, hence more TESP by trying to shove more CFM through the existing
Sometimes, just go to the hvac-talk.com wall of shame and see all the bad
ductwork installations, many being a "ductopus" using flex duct.
Yes, and here is why. Your average PSC or split-phase induction blower
motor on high runs at a fairly constant speed (a 4 pole motor can only speed
up from its rated speed, usually 1725 RPM to just under 1800 RPM @ 60Hz).
With a centrifugal blower (squirrel cage) the torque load on the motor is
directly controlled by the amount of air flowing through it (ande vice
versa), hence as you restrict the airflow (increase the SP) say with
undersized ductwork the blower unloads. Less torque at the same speed means
less HP (HP=torque in ft-lbs x RPM / 5252) hence less motor watts. An
underloaded motor is less effecient but lasts longer. Too little TESP on a
system with an induction motor can actually overload the motor, hence why
old systems that had belt drive blowers usually has a variable pitch sheave
on the motor. The belt ratio hence wheel speed was adjusted to run the
motor at full load with a new system. As the ductwork and/or filter got
dirty the TESP went up and the motor unloaded some.
Now here is where it gets tricky, ECMs as used on indoor blowers are
constant torque NOT constant speed. The shaft torque is held constant hence
the airflow is held mostly constant. Increase the TESP on these systems and
the blower speeds up either till the torque/airflow goes back to rated or
till the motor hits its top speed limit. More RPM X same torque / 5252 More HP = more watts. More watts x same airflow means hotter electronics
hence shorter life. Add in a plugged filter and the poor little motor runs
its little heart out at max speed with little cooling airflow till it burns
As said this depends on TESP. At high TESP the ECM can use more watts than
Electric resistance heat is usually more expensive than gas heat and in the
summer it is just more sensible heat load on the evaporator hence more watts
A while back I came across a study done on the savings of ECM blowers
in residential HVAC
applications segmented by geographic regions/climates. One key result
of that study, which
I didn't expect and I believe is reflected in what you say, is that
how much energy one saves
depends to a large extent on the duct work. The greatest savings came
duct work, ie lowest pressure. Next was good duct work, which also
less savings. Duct work they classified as typical still got
savings, but much more modest,
maybe 15- 20% in electricity cost. However if you have poor ducting
there can be no savings
or even a net loss of up to I think about 10%. The energy savings
also obviously depends on the climate.
But I think HomeGuy has a vaild point, at least to some extent.
Whether you can recover enough
in energy savings on an ECM versus the increased upfront cost as well
as the real potential for
higher repair bills is questionable. I've seen horror stories here
of the ECM electronics fried
by power surges for example and a $600 bill But I've never heard of
a conventional furnace blower
failing from a power surge. Also, I think you'd agree that if
improper duct sizing can screw it an cause it to fail, it's entirely
possible that some contractors who don't know what they are doing will
result in the motor failing
at some point. And if that point is after the warranty is up, then
This same faulty logic is frequently applied to water heaters with
claims that the standby
losses from storage tank models helps heat the house. For some
reason, they completely
forget that for most of us with AC, that gain turns into a loss in the
On Dec 6, 4:22 pm, firstname.lastname@example.org wrote:
If a power surge fried the blower it would have got the control panel
first. With any new unit you should be doubly sure its surge protected
and well grounded since you will have alot of electronics. When I got
my install they offered to somehow test my duct airflow, thats where
shopping for the right pro is important. I heard those motors were
redesigned a few years ago to separate the electronics from the heat
of the motor, since the electronics were what failed and now the motor
and design has finaly matured.
Not uncommon, actually. Upflow unit replaced with downflow
unit ... presto.
Gas fittings / pipe 'held together' with duct tape .....
One of my 'most memorable' discoveries long ago - Imagine a
typical kitchen from the 70's. Stainless steel sink, electric
4-burner in-counter stovetop right next to it.
Accidently touch the chrome trim around the stovetop and the
sink at the same time - get knocked on your ass.
Oh - house occupied by two old folks in their 80's.
Lift the stovetop to find - a wire burned off the burner
connector, so someone ( a PAID 'repairman' ! ) strapped it to the
OUTSIDE of the burner element with a worm clamp.
Click here every day to feed an animal that needs you today !!!
It is quite possible. A belt drive blower could put up with an awfull
Not necessarily - but if the installer does not do the temperature
rize test and properly set the motor speed, you could get a failure
due to improper installation.
You underestimate the difference in efficiency between a standard
induction motor and an electronically commutated DC motor,
PARTICULARLY with multi-speed AC motors.
At lower speeds ECMs can save over 60% of the electricity used by PSC
For example, in low speed circulation a typical PSC furnace motor will
use 350 to 500 Watts while an ECM will use 75 - 125 W.
You need to read the entire study at:
but an interesting part is the following - with the same airflow,
"The power use of the ECM and the PSC motor were measured in one-time
tests using a Nanovip power meter. The ECM used 16.5 Watts in
circulation speed and 284 W in heating speed, while the PSC motor used
350 W in circulation and 490 W in heating. Thus, the ECM used 58% as
much as the PSC motor in heating speed, but only 5% as much in
circulation. The ECMâ€™s flow rate was almost identical to the PSCâ€™s in
heating speed, and was 47% of the PSCâ€™s in circulation speed."
The National Research Council study quoted shows 206 watts difference
on high speed, and 330 watts less on low speed.
Except when running the AC - and gas is cheaper than electricity for
Or do as the National Research Council did, read the study - very
Actually, they are finding the ECM to last at least as long as the AC
motor in many tests. (in part because they run cooler).
The motor control electronics are the least troublesom of all the
controls on modern furnaces.
I've replaced too many thermocouples on standing pilot furnaces - and
NO electonic ignitors so far on the new furnaces. Average lifespan of
my thermocouples has been less than 7 years (5 in 22 years on my own
furnace, and 5 in 7 years on my friend's gas boiler) I'm on #3 on my
water heater as well.
This is, I believe, year 8 on the electronic ignition furnace.
The blower in my furnace runs at low speed 100% of the time that the
furnace is not running on high for heat or a/c. (for air cleaner and
If the furnace NEVER kicked on, the ECM saves me 2890kwh per year.
(330 watts X 24 hrs/day X 365(90800 wh).That's $232 at $0.08 per
kwh. and that's not counting the savings when the furnace is actually
running. And the actual cost of electricity is more than $0.08/kwh
here when you add in the distribution charges and everything else, and
throw on 13% HST
Actually, IF the condensing furnace is 7% more efficient than the
equivalent non-condensing furnace, (97 vs 90) the fuel savings will be
about 8%. With my total annual gas bill of $700 (part of which is my
water heater) my maximum total gas savings would be less than $56 per
Not a very attractive payback, particularly if I end up replacing the
secondary heat exchanger in 10 years.
When it comes to discussing the pro's (or perhaps the lack thereof) of
ECM motors for use in HVAC air handler systems, I've found that this
document is very informative:
I have pasted the conclusions of that document below. It basically says
that the benefits of ECM motors are lost in installations with high
static pressures (and something that I bet a lot of home-owners don't
want to fork out money for is to re-do the duct-work in their homes).
Perhaps someone else can explain why the flow characteristics of a duct
system is described in terms of the back-pressure it generates instead
of speaking directly about the RESISTANCE of the ductwork, even perhaps
putting a number on it (which surely can be done, given that we might
know the CFM and the air pressure at the input side of the duct, and
assuming the pressure at the far end is zero). When someone is talking
about high static pressure, they are essentially saying that the duct
system has a high resistance to flow (caused by any number of reasons -
closed or blocked vents, small-diameter ductwork, long runs of
small-size ducts, turbulence caused by right angles, filter too small or
too dense, etc).
Which could be why my idea that the gating of furnace output around the
A/C coils is not appreciated as something that can reduce airflow
resistance (ie - reduce static pressure).
As someone who's been living with and has experienced HVAC systems with
single-speed AC fan motors, I really can't appreciate the need for a
variable-speed fan motor. All this discussion about how PSC motor
efficiency drops to 15% - 30% when used at low speeds is a real mystery
to me - are there really furnaces out there that have the necessary
electronic controllers that will use PSC motors in such a variable-speed
capacity? Why no real discussion about the efficiency of 2-speed AC
I also don't understand how running a fan at low speed is better at
humidity removal when the HVAC system is in A/C mode - yet ECM makers
make that claim.
Claims that ECM motors are just as reliable as PSC are also a crock,
given that none of them could possibly be in service yet for 30 to 40
years as is the typical PSC motor to even begin such a comparison.
Youtube video showing badly-behaving ECM motors:
These ECM motors look really flimsy - like the 1/8 hp electric motor I
have on my roof for my attic fan. Sorry - I wouldn't want something
that wimpy in my furnace.
Apparently they are somewhat succeptible to lighting strikes (lightning
doesn't have to hit your house directly to dammage the electronics in
your house). I guess your entire furnace is more succeptible to
lightning when it's got it's own computer. Another strike against the
The main conclusion that we would draw from this study is that although
the use of an ECM has the potential to reduce fan electrical power draw,
much of the benefit is lost in systems with excess static pressures. A
full analysis of this problem was done by Lawrence Berkeley national
Laboratory (Lutz et al., 2006). In other words (as in many cases in the
building industry) the benefits of high technology can be defeated by
poor design and faulty installation or implementation. Problems can
include excessively constricted duct designs and installations,
restrictive return plenum fittings, or excessively restrictive filters
(see “Is There a Downside to High-MErV Filters?” HE nov/Dec ’09, p.
However, with better designs, air handler efficiencies can be
improved—significantly beyond the typical values assumed in previous
work (that is, 2.5 CFM/W or 0.4 W/CFM). This is especially true when a
given air handler is used at the lower end of its speed range. For
instance, a 1.5- to 3-ton unit being used at 2 tons air flow at 0.5 IWC
static pressure has an efficiency in the range of 3.7 CFM/W (0.27
W/CFM). Of course, reducing air flow for a given size of outdoor unit
can have negative consequences, such as reducing overall efficiency
(SEEr and EEr). But this factor can provide additional ammunition when
arguing for tighter sizing of cooling equipment, and/or two-stage
equipment with a variablespeed air handler.
In other words, if you can keep the air flows down (all other things
being equal), you are giving your ECM a better chance to achieve high
CFM/W efficiencies. The measurement of air handler efficiency is
relatively simple; it can be done mostly with gear that a home
performance contractor is likely to have. an air handler powered from an
electrical receptacle can be quickly measured with a plug-in power meter
such as a Kill-a-Watt. However, power measurements are more
time-consuming if the air handler is hard wired. But overall, increasing
the data set of installed ECM air handler efficiencies could be very
informative, as would measuring and recording the operating external
static pressures for these units.
LOTS of furnaces and AC systems with multispeed PSC motors - and they
are terribly inneficient at low speed. And there is virtually no
"electronics" involved. On my old furnace it was just a relay - the
fan ran on low speed continually untill the furnace called for fan,
when it kicked a relay that put the power to the high speed windings
instead of the low speed.
The AC runs the fan at HIGHER speed than the furnace on my new system
- but runs the fan constantly at low speed when the AC or furnace are
not calling for circulation.
My PSC lasted less than 20 years. It was a 1/3hp belt drive - replaced
it with a 1/2 HP
Some are wimpy, some look just like a typical PSC motor - and the PSC
direct drive motors WERE wimpy - and many didn't last 10 years.
IN ALL cases, the benefits of high technology can be defeated by poor
design and faulty installation - doesn't matter what field you are
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