Are there any real safety issues with oversizing a blower motor on a gas forced air furnace. Say you have a 1/2 hp 1075rpm motor, and you replace it with a 3/4 hp 1075rpm motor, and size capacitor correctly. Both motors are four speed motors. Both are same physical size. Im curiouse about the hp difference, what problems could this cause(not in theory, but in reality). Just wondering for emergency, temporary fix to get someone back in heat, when no other options are readily available. But curious if it can be left as a permanent fix, with no forseen problems.

PS. Furnace is out of warranty , so warranty is not an issue.

As long as the amp draw rate is not exceeded it will run just like any other motor would. I can see no harm in fact I have one of my air handler units is stuffed with a much larger HP motor cause it was what I had on hand 15 years ago when the original cheap motor took a hike. It has been running great for 15 years with no problems. Now I have to admit I have pretreated all my personal use motors with a product called Tuff Oil. I mix it down with turbine oil and lube them well before the install. Then every 5 years I revisit the motors at give them a squeeze with the same mix out of my zoom spout oiler that I keep around for such occasions. I have been using that product for about 30 years and have never lost a motor yet. Never used it on customer motors over the years since I was in business to make a profit if you know what I mean.

I have taken sleeve bearing motors that were pretty much stuck and lubed them up with my special sauce and they are still running years later. My kitchen exhaust fan is a prime example. I did not have a replacement motor on hand 10 or so years ago so I lubed it up with the sauce and got it running. I went out a bought a replacement motor and figured I would replace it. Well the motor is still sitting in the garage with a lot of dust on the box. Call me lazy but I figured as long as it is running why replace it.

Remember a larger HP motor will not be running at its maximum when a smaller one will given the fact that they are moving the same amount of air. The higher HP motor being designed to produce more HP than the smaller one and will be coasting so to speak when the smaller one is running its heart out. A Amprobe is your best friend when playing with such things.

Thank you so much. I was thinking that there wouldn't be a problem with this, but I didn't have anyone to ask(not going to ask the manufacturer, because you know what they will say,, replace with exact motor. You said exactly what I wanted to hear. I could never figure out how it could be a safety issue. Motors have internal overload protection, and if motor fails, its up to the other safety components in the furnace to take control of the situation. Worst case, motor fails, best case, it last for years and years.

I would think that a larger hp would actually last longer, since it is coasting. Amp draws were well within limits, from low to high.

Thanks again, I will sleep much better tonight.(now that's a lie, I've got plenty of other things to worry about that will keep me up )

Take care, and know that I can't express enough how much I appreciate your input

I do not have all the answers but if I do have the answer you are always welcome to it. Have a good weekend.