Why the heck would you need a variable speed blower? That doesn't even make any sense to me. I was pricing a new system until I noticed that your only choice was a variable-speed blower unit, which of course bumps the price up.
Idk why variable speed blower would be your only option. One thing pushing towards that is the quest for energy efficiency. An ECM motor is more efficient and when you have that your a good ways toward variable speed. Variable speed let's it spool up and down very quietly. It is also useful with two stage furnace or AC. Downside is if it fails they cost a lot more than a regular motor. I have one, 8 years now, no problem, lower electric bill. On the other hand the ECM fan motor on the condenser failed. It was 350 for a new one, so for 90 switched to a regular, split-phase one.
Coupled with the two stage you can also have a much more even temperature at a given setting. I thought about it for this house as they offered a couple of options but the cost was way too much. Couple of hundred I'd go for but it was thousands more.
It is all in the game of numbers. By changing the speed of the motor as the heating and cooling coils change the efficency numbers can be fudged a bit. I am thinking with heat pumps you need more air flow for cooling and less air flow for heating. Probably does not make much differnece in the long run, especially if you figure in the cost of the motor and controler.
If you have a variable speed air handler and the or board motor goes, plan on $1600 plus labor (based on a Trane TWE) because they like to replace the board and card as a set. The guys say if one is blowing the other, you will end up doing both anyway after you buy one. I went the $300 route and had him put in a contactor and a regular motor. (parts and labor). The couple bucks a month I may be spending will go a long way before I spend $1750 ($1600 parts, $150 labor)
Then the company was probably playing games. If you look at the actual eqpt, the cost difference is a couple hundred bucks, assuming it's just the variable speed blower, which when I was looking, you could get at least from Rheem. The whole cost difference between a basic 80% nat gas furnace and a 93%, two stage, variable speed was maybe $600 cost of the actual furnace, like $1300 for the basic, $1900 for the better one.
A variable speed blower allows the system to be precisely ballanced for "heat rise" in heat mode and temp drop in cooling moce
You have to check the temperature rise, supply temp off the plenum (in the main duct) minus return air temp and compare it to the rating plate.
You may only lower the heating speed if it's not already on the upper end of the range (check the nameplate, it will list something like 40 to 60f) and re-check the temperature rise after.
You adjust it by changing the taps on the board, moving the heating speed tap to spare and using another tap.
Before you make adjustments, you should clock the gas meter to ensure the fuel input is correct. Google how. If it's not, the temperature rise reading means little and you need to call a service tech to change the gas pressure before changing blower speeds.
It's absolutely pathetic that you've called out a service tech and he doesn't even know that you can change the speed or how - unless it's just an excuse.
When they install the furnace, they're supposed to commission it; setting the fuel input to match the rating plate (there's an acceptable gas pressure range, like 3.2" to 3.8" - allowing for some fine tuning - they can change orifices in high altitude and propane applications if needed) and setting fan speed for proper temperature rise. Every duct system is different, the fuel content of the gas varies depending on location so the factory settings are not always correct.
If he doesn't know to adjust the fan speed, he hasn't been commissioning furnaces properly and is short-changing customers.
The 80% afue rating only applies with the correct fuel to air mix and proper airflow; an out of tune furnace will operate below it's efficiency rating.
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