View Full Version : Furnace comparison
09-10-2009, 01:18 PM
What are the differences between single stage and two stage furnaces?
What is the difference between a Variable Speed blower, a Single-stage electronically controlled programmed ECM blower, and a two speed blower?.
I am looking at these three Carrier furnaces:
58MEB, 58HDV, and the 58 MTB
Pros and cons of these furnaces?
09-16-2009, 06:48 PM
If you have as many posts next to your name and you are not a homeowner, then I feel for you if you are in the HVAC field if you don't know the answers to your questions.
09-16-2009, 07:21 PM
Call me, I'll gladly install your next, and last, furnace!! lol
09-16-2009, 08:51 PM
In the past furnaces were either on or off. A furnace SHOULD (but rarely is) sized properly for the coldest day of the year, meaning the rest of the year is oversized. That leads to lots of on/off cycling and less comfort. So the industry went to 2 stage so furnaces had a low fire for milder weather. Latest technology is 3 stage or modulating meaning lots of stages. These furnaces are for comfort, efficiency is the same as a single stage.
In the past furnaces had conventional motors. They ran a fixed power on 1-5 preset speeds. As the filter got dirty or registers were closed, airflow dropped off. These motors aren't efficient either. The latest technology, ECM or electronically commutated motor, uses much less juice and has more flexibility over speeds. First use was variable speed motors that could sense duct restriction changes and vary themselves to maintain the desired airflow. Now, to keep costs down, which is what most consumers want, the industry cheapened the system to make them function liked the old motors but use less electricity like the variable speed motors. They still have more control over speeds but do not vary to maintain airflow. More restriction in the ducts means less air.
The MEB is 1 stage with the non variable speed high efficiency motor technology. The HDV is 2 stage fire with a variable speed motor. It runs 93% efficient in upflow, 95% in downflow & horizontal installations. The MTB is 93% 2 stage with non variable speed high efficiency motor. It runs 91-95% efficient with 95% being only the 40,000 BTU size in upflow.
The best bet would be something at 95% rating to get the federal tax credit. That would be the HDV only in downflow or horizontal installs or the MVC in upflow. It's 3 stage and variable speed.
09-17-2009, 12:17 AM
Many thanks. That was a concise, informative answer to my question. Thank you.
09-17-2009, 07:02 AM
The MVC would be your best option, Carrier is going to stop making the MVBmodel furnace I think at the end of this year or shortly after the first of the year if they haven't done so already. The MVC is a very nice furnace as long as you go with the Infinity controller paired with the furnace.
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