I really need to figure out a way to have my cats live outdoors (6 months old). They're stinking up the whole house. I'm going to buy a cat house on Amazon, but I'm not sure how to keep it warm. I feel bad for those guys being in cold temperatures when they're used to being mostly indoors. Should I try to make it warm and toasty for them? Or is it OK to just give them like a heated pad to lay on?
I agree with M.Mat, kittens or even cats that are used to inside shouldn't be placed outdoors. Those outside cat houses, some that are heated, are usually used for strays that frequent an area but refuse to go inside due to probably being feral or just afraid of humans. Cats outside are in danger, especially during the cold, wet, and at night. Even if they manage to be kept safe from outside attackers, cars, and any other dangers in your area, they still have to deal with constant weather elements and as kittens, people usually take them inside to save them from that hard life of a stray. It's never really a good idea to turn a domestic cat into a stray cat.
If the litter box is bothering you, then it might need to be changed more often. I have two cats, one that is prone to UTIs so I find myself scooping my litter every other day rather than waiting the week, like my sister, who has one cat, does. She also has 2 litter boxes for her one cat. I have two litter boxes for two cats. I have them side by side because I notice the cats naturally using one box for poop and the other box mostly for pee. You can choose to spread them out if you would like especially if you notice a room that they are spraying in. Often times cats will pee in the same spot every time.
Also make sure you clean the area they marked with a urine remover or bleach everytime they pee to ensure the odor is gone. Cats will remark an area if they smell the urine of themselves or another cat. I, for one, do not like the smell of litter as well which is why I change it more often (it's in the corner of my kitchen so I do not want the smell of litter box to be overpowering the smell of my kitchen).
If they are marking or peeing outside the litter box, it might mean they need changed more often, need more than one litter box (especially with more than one kitten you probably need more than one litter box), or need a litter box with a lid. Some cats do not like to use a litter box with a lid so keep an eye on that problem. I also changed my litter to be clump and seal for multiple cats. I used to use tidy bowl but found the smell of the one cat's stronger smelling urine (which is a side effect of her being on special more acidity food to prevent UTIs), to still be smelled after a day of her using the litter box. My sister likes tidy cat so it's a personal preference I guess. Sometimes a change to multi-cats, or to a different litter can be the answer. Maybe all four changes will help the smell of your house if that is related.
So, cats are very clean creatures. If there is odor, assuming you mean cat box smells, you need to clean it much more often. Cats don't like the smell either so they may be going outside the box.
Kittens six months old are too young to be outside unattended. There are dangers outside they are not equipped to deal with since they have been inside with humans: other animals--especially other cats, car traffic (they won't stay in the yard once they acclimate)--they can easily get hit by a car.
There are a number of issues brought up by your inquiry. Are they spayed/neutered? Vaccinated? A heating pad outside is a fire danger and shock hazard for them. It will get wet and they are likely to chew on the cord. VERY DANGEROUS AND NOT AN OPTION. Check back in and let's try to find solutions for you AND the cats.
First of all, cats 6 months old are too young to live outdoors, so please wait until they are at least one year old. You don't tell where you do live so it's not easy to give advice. There is some difference if you are living in the Arctic or in the tropics.
The most important thing is to keep the cat house out of the wind and in a place without direct sun. This means that if the temperature is in the range of minus 5 to plus 30 degree Celsius, cats might have a good life if they are provided water and food in the correct quantity. (I hope it never gets below freezing where you do live, as this is bad for cats and people; I live in Norway and know this).
The question is "How do I keep my Cats warm in outside cat house?" That is a valid, and pragmatic question. I offer a pragmatic answer.
The issue here is that house cat corporal temperature is higher than most mammals I know of. Average cat temperatures hover around 102 degrees F (39 °C). They normally seek higher temperatures to preserve body temperature while in 'park mode'.
You may have noticed that most of your animals like to sprawl out half in the sun, half out on a warm clay patio... this is part of their amazing energy-saving system.
What I learned from that...
When I built my dog coop, I installed low-wattage red bulbs in the peaked roof, out of reach of my guys... If you want to get sophisticated, you could substitute IR reflectors; (most of those fall into the 75-150 watt range); but as an electrician I can say that is only recommended for a a space of 5-6 cubic meters on a timed cycle.
It takes a single 25 watt bulb to keep a one cubic meter enclosure warm even in zero-degree temps, provided the house has thermal roofing, and the wind is not fierce.
The other issue is training your guys to use it...
BTW...before buying anything on Amazon I suggest you take a very close look...there have been a number of electrical issues with some of their products recently...