The needs of a Manufactured home are different, so you need the correct size furnace.
The link below may help.

Here is a link that might be useful: Manufactured home furnaces

We replaced the old heater/AC unit that came with our MH with an energy efficient heat pump. Our power bill is now less than half of what it used to be. You just have to get the right size for the sq feet of your home.

Hi cathyyg, the Mh I just bought had had a non-working furnace for three years. My research concluded a new furnace, specifically built for MH, would cost about $550, plus shipping charges. Further research told me a professional would charge about $90 an hour for installation and figured about four hours. All in all, I was looking at close to $1,000. (I live in eastern Washington state.) Unacceptable, lol! I found a seven year old, completely refurbished furnace at a local second hand store for $200. It was not a "MH furnace," but the size was right. The owner of the store even came out and looked at the non-working one to make sure it was the right size before he'd sell it to me. I figured it wasn't rocket science, so with the help of a retired neighbor who's a fabulous handyman, I installed it myself. It took the better part of a weekend, since we were novices, but I saved $800, and got to know a really nice person in the process. Hope this helps! Oh, and I can say, two weeks later, reports are that the house is comfy, cozy warm!

I ended up doing nothing about my furnace. I wanted to replace it with a regular furnace of appropriate size to deliver the HUD mandated volume of air, so that I could get a Real Filter. This Intertherm downflow M-1 has no filter, really, just one of those cheesy pig hair things on the inside of the louvered door to the furnace closet. I was willing to spend several grand on this, but nobody was interested in doing it. So I am doing as the nice manufactured home repair guy suggested, and just using a better filter on the inside of the closet door. My allergies are not happy about it.

Hi Cathy, sorry I've been MIA--I'm dealing with a health crisis atm, which hopefully will turn out to be a non-resistant systemic infection. Anyway, I wanted to say I'm so sorry you weren't able to get the furnace you wanted, especially when you are suffering with allergies! There is no reason in the world why you shouldn't be able to get the furnace you want! I'm continuing to be amazed that there are so many tradespeople who flat out refuse to work on manufactured homes! And especially when you were ready to drop some serious cash on this! I encourage you to not give up on your quest. There's got to be somebody out there who can do this for you. I know you shouldn't have to do this, but maybe offer a $100 "tip" to the installation guy? I'm blessed not to have allergies, but both my brothers do, and I've seen how miserable it can be. Good luck, and maybe try again after the holidays? :-)