Just had a new furnace put in and wow! What a difference! It's got a DC motor and it is made so the fan runs all the time. But there are no more cold spots in the house and the temp really does not vary in the room. I'm just amazed. Who would have thought?

Infinity 96 Gas Furnace - 59TN6 | Carrier - Home Comfort

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You don't need a weatherman to know which way the wind blows - Robert A. Zimmerman

That sounds nice. I still have my original furnace and ac unit at my house which we built in 1991. I run the fan all the time to help keep the temp even but with three stories its still always warmer upstairs and colder down.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

i use a 2000 carrier heat pump. I intercepted the wires going to the 220 volt strip,and put a switch.That way only the compressor runs,and saves me money.when temps go below 21f I then move switch so electric heat can help the pump.

Good idea!

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

What's the advantage of a DC motor? How difficult is it to diagnose problems on a newer furnace like this? I've got a number of pretty old furnaces and I like their simplicity.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

could you run a dc motor on a battery?

Easier to control and the motor can drop down to very slow speeds. It is continuously variable in operation.


. I too prefer simple but unfortunately the efficiency of the more complex furnaces is too great to ignore depending of fuel costs. In most cases they will be more expensive to fix as well.

Yes but the battery voltage has to be in the range the DC motor is designed to operate at. If the voltage is lower the motor will run slower. You have to watch your motors more in todays world. Some motors are three phase but powered by direct current through a phase generation device. These are great variable speed motors. Becoming more common I suspect. Having no brushes and commutator to limit efficiency makes a world of difference. Plus brushes are a wear item. Brushed dc motors also make electrical noise. So does the phase generating device but less.

When you see three primary wires entering a motor today be careful. Especially if you see a fourth wire that is ground. Unless it is a fixed two speed fan motor for example. It may be a three phase motor even though they call it a DC motor. The other warning the motor you may be looking at is not a normal dc motor is the casing or frame size. A three phase dc motor can produce a lot of power and does not require parts very large to do so in comparison to a normal dc motor. To reverse the motors running direction you just reverse any two of the three wires entering the motor from the phase generation device.

I have about a dozen of this type of motor for specialty use. Since this area might be new to some I went and got one out to describe. On the package it is described as a neu castle motor. A sensorless brushless motor in the 1700 series line. Actually a model 1717. Every volt you supply to it spins I at 1500 rpm. You can add volts until it gets to 40,000 rpm max.

I assume above that it would fly apart internally from centrifical force. You should be able to find these motors under Castle or neu on the web. This motor as almost all of them are produced in China. I estimate it weighs about two pounds. It is probably in the 1-2 horsepower area.

Actual horsepower is seldom specified on these smaller motors. It makes substantial heat when running hard so you have to liquid cool it preferably. In fact this type of motor has made the electric car possible. Now if they make the case or frame size larger the need for cooling can be reduced. Then simple fan cooling is reasonable. The neu motor of the 1900 series group is only a little larger but claims 5-6 horsepower output on acceleration.

I suspect again without knowing some manufactures may be currently using them as car heater motors. Designed and built for simple functions like that they would be cheap enough. To get the operational revolutions where the designer wants them is done by the number of windings on the rotor. A simple fan motor of this type would not generate enough heat to be of concern. Again I double checked and they are reffered to as DC motors so be careful.

I may be way out on a limb here. Twenty years ago a new gas furnace I examined was already complex enough. I expected it would have some form of self diagnosis as to an existing fault. They may have become even more complex since. Yet that one I looked at was already complex enough.

I do not think oil furnaces have evolved as far as gas furnaces. Parts in general are not as cheap when needed like the older furnaces either in general.

Maybe you are as cheap as me. There are usually all kinds of good used parts around for old furnaces. In fact I usually have enough on hand to fix almost anything. Although I do not reuse limit/fan switches.


Well unless they where to appear almost new I imagine. That has not happened yet.

My approach on HVAC equipment has been to specify simplicity and quality when possible. My house and all my rentals have 65% effecient or so furnaces. The very efficient running is of course nice, but one service call can eat up four or five years of fuel savings. That said I have not bought any for probably at least 10 years as all mine are still going strong. Everything has conventional metal chimneys.

I have replaced the blower in my furnace at the house and the outside unit at my carriage house.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The DC motors in modern furnaces and boilers are, oddly, designed to operate on A/C. The advantage of DC motors in these applications is that they can be PWM controlled, so the speed is infinitely variable. Incoming AC current is electronically rectified to produce a PWM feed at the desired duty factor. So no, you can't run them off batteries.

I use pumps with DC motors (Viridian 2218's) on my boiler. The pumps have ECM logic cards that continuously adjust the speed so that the return water is 20 degrees cooler than the source. This allows the pump to run almost continuously and produces a very even heat. When they start up they are at full scream, and then slow down as the spent water comes back around. I've been very happy with them.

I don't know, but it's nice and quiet. They diagnose it through fault codes. I don't do my own furnace anything so I really didn't consider the maintenance portion of it.

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You don't need a weatherman to know which way the wind blows - Robert A. Zimmerman

Sorry about my long warning. At the same time somebody could get into a real mess by just assuming.


If a furnace is really high tech the common failures or how to read the trouble codes are probably up somewhere on the web.


Anyways the furnaces will have an initial warranty period and perhaps ongoing service contracts might be pretty cheap after than.

We had a new 96% efficient Armstrong Air forced air furnace installed in the fall of 2015 which replaced the unit that was installed in 1956. The new unit is much quieter, and quite efficient compared to the old one. Cold spots are a thing of the past in this house. I don't know much about it other than the fan is always running, but at variable speeds according to temperature. It came with a whole home dehumidifier as well as central air conditioning, which the old one didn't have. I can control the humidity of the house, making it more comfortable year 'round. My costs to operate the system is less than half of the old unit, which means that it will pay for itself in a short time.

The only thing I don't care for about it is the filtration system used...the filters run me about $45 each, and are replaced 4 times per year. The furnace guy said that he usually puts a different filter box in, one using normal filters, but didn't have one on his truck when he did this one. The filter is an accordian style with a ton of surface area to trap allergens and dust, and does a great job at it apparently since the wife said she has to dust the house much less often than before.

All I know is that I'm comfortable year round and pay less per month to be that way.

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1987 560SL
85,000 miles