kerosun and coal

can i vent a coal furnace and oil furnace out the some chimney? also the chimney is about 70 years old and not lined is it still safe?

In most areas, building code prohibits connecting appliances using different fuels to the same flue. Having said that, I have heard of it being done but (IMO) I do NOT recommend it. If the oil burner is to only be a back up for coal burner failure then I would disconnect the oil burner from the chimney and connect oil if/when needed. If both furnaces will be needed to handle the heat load, maybe you could power vent the oil. Multiple appliances connected to the same flue can cause draft issues because the idle appliance(s) can still have draft flowing through them robbing draft from the in service appliance. Fly ash could accumulate causing problems where secondary appliance connects to flue of in service coal unit. It's just better for each appliance to have it's own flue.
I bet your chimney is good but you need to inspect it the best you can or have a pro (chimney sweep) do it. You could use a mirror reflecting sunlight down the chimney or tie a bright flashlight to a rope and lower it to inspect chimney for loose bricks, holes etc. Be sure the clean out door(if there's one) closes tight and secure, seal off any other openings into the chimney.
I assume you have been using this chimney with the oil burner with no problems so it should be fine.
Be sure to have carbon monoxide detectors in place. Safety first.

i would be acually using kerosun.would putting a damper on the oil furnace help. they was never used together before. the coal inlet is below the oil inlet. the oil furnace was put in and the coal heater was taken apart. so now i want to hook up the coal heater but dont know how well it will heat the house. i want to leave the kerosun heater as a backup if the coal fire goes out at night so the kerosun heater would kick on and keep the house warm. how would i direct vent the kerosun herater?i want it to be as safe as possible. also do you know where i san get replacenrnt shaker grates? the only thing i can find is it is a thermomax 622?

Since you want oil/kerosun to be an automatic backup I would powervent it and connect the coal to the chimney. There's a lot of powerventers out there nowadays and I think this would be the best for an automatic backup switchover setup. http://www.fieldcontrols.com/venting.php
I think that is the best way to do it.
As far as replacing the grates, you may have to get measurements of the existing grates and look for a match. You can get grates at this site. http://www.woodmanspartsplus.com/h343/Home.html

thanks for the help but i dont see the grates i need i need the outside round grates with a center dump. the center ones are good but the outsied ones are broke. it looks like it is a 2 peice set i need

would it be of any benifit to put a 4"liner up the chimney to the top for the kerosun heater and just run the coal outlet in to the chimney?

I would have absolutely NO problem venting an oil/kero fired appliance and a coal fired appliance together, damper not needed either provided the chimney will provide sufficient draft to both appliances. I would actually reccomend FOR this type of setup vs. powerventing or disconecting one appliance and reconnecting it when needed. be sure to periodically check for flyash buildup in any horizontal sections of pipe if you use a stoker regardless of whether or not you're running the appliances in the same stack or not. I would NOT mess around putting a smaller pipe inside the flue or any such stuff- there's absolutely no reason for it whatsoever! just run the two together and be done with it. as was mentioned code prohibits it, but for reasons related to woodburning that don't apply here. in my home I have three appliances in the same flue, water heater, gas furnace, and stoker furnace- works great in an 8/8 tile flue and i wouldn't have it any other way.

ok thanks allot for everyones help