Most central heating systems can be equipped with HEPA fillters that filter allergens. These can be purchased at most home improvement stores such as Home Depot and Lowes. There are no central heaters that actually do the allergen filtering without the use of a replaceable filter.
Heaters for what purpose?
California has the strictest regulations, so if you can, buy heaters from there.
Family Facets offers a variety of water heaters, including wireless water heaters, instant electric water heaters, instant electric water heaters with remotes, mini tankless electric water heaters, and more.
Unfortunately, heaters can put out over 1,000 Watts, which is far too much for any battery assembly to power.
You can purchase water heaters at any home improvement store like Lowes or Home Depot.
You can find in-line water heaters at any of the Home Depots in NYC, or at just about any plumbing or electrical store.
An air purifier that does not use electricity or energy of any kind is merely a filter. Filters block dust, pollen, and other allergens from getting into places where they shouldn't go. Since they have no way to draw in air, they rely on outside fans or the wind to help them filter the air.
There are many drawbacks to ventless heaters. One drawback is that acidic byproducts may be created because of combustion. Water vapor may also be created by ventless heaters.
A fish bowl. Or even a bathtub... any thing that holds water. But it's est to have a aquarium with a filter and one of those heaters. Otherwise, your fish might die pretty quickly.
Tankless water heaters are low energy because they only run when the hot water is needed.
Good, but expensive to operate.
Oil heaters can burn badly if touched when hot. Obviously. oil is dangerous if it gets into any wounds, eyes, or the mouth when filling them.