BTU rating of a standard automotive heater core?

[BioHazard]

I'm designing a bit of a hydronic heating system in my head, considering having several different zones each powered by an automotive heater core with fans mounted to the back of it. Sort of a forced air/hydronic hybrid system. Part of the reason for this is because it's easier to run PEX water lines than air ducts in a completed building.

Can anyone tell me roughly what the BTU rating of a standard car/truck heater core would be? Something like this for example:
http://www.ebay.com/itm/Heater-Core-Four-Seasons-Rockhill-94553-Chevy-GMC-Pickups-Suburban-1973-1991-/220926107439?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item337038df2f

[Ronmar]

Absolutely nothing to back this up but experience, but I am guessing that it is around what you get from a small 1000W forced air heater...  As a guestimate, at least for the Toyota cores I am familliar with, that is about 6-8 KBTU maybe.  Can't follow a ebay link at work, so havn't seen the one you pictured yet to see wether it is larger or smaller than what I deal with...   FWIW:)   

[dieselgman]

Total capacity will be affected by input temps and fan efficiency but my off-the-cuff estimate would be quite a bit higher than 8000 btu. We have used small Caterpillar cores rated around 15,000 btu I believe. I don't really know what that old Chevy core might flow, but should not be drastically different than any of the small import cores. We have also salvaged some very good mid-sized heater cores from buses before, that would be a good place to look if you have any junkyards with that kind of stuff near you.

dieselgman

[Tom Reed]

If going that route, why not just use standard hot water baseboard heaters?

[quinnf]

That should work great.  I'd expect max of 12000 BTU or thereabouts with it, but the waste heat available from a 6/1 running flat out is about 15-17000 BTU.  Lots of restriction in heater cores.  Don't expect a lot of water flow through it.  I think those were 5/8" or 3/4" ID hoses.  If your main line is larger and you hang 2 or more of these off the side with some judicious use of gate valves to make the water flow where you want it to, and maybe an electric boost pump to help things along, you should be able to make it work.

Quinn

[DanG]

An auto-style exchanger is designed around temperatures around the boiling point of water - even water above boiling under pressure. You will not get the BTU output without it, especially if long plumbing runs in narrow tubing....

[BioHazard]

If going that route, why not just use standard hot water baseboard heaters?

Honestly, I've always hated baseboard heaters. No particular reason....

Right now I'm in the inspection stages of buying a 3 family property with 3 enourmous shops. The main house was built in 1928 and currently has electric heaters. What I would really, really love to do is setup my own miniature "district heating system", providing hot water to all the buildings from a central heat storage tank. The heat would be generated from a combination of a wood boiler, waste oil boiler, and some engine heat. There would be a massive network of pumps and pex and thermostats all over the place.

Basically what I'd like to do is build several heat exchanger units that can be mounted in different places, all with a simple heater core inside. Some places, like the shops, would obviously get much bigger radiators. I know I can buy such things pre-made, but you guys should know by now I'm a cheap bastard. 

[mobile_bob]

keep in mind that the btu rating of any exchanger goes down dramatically with reduction of coolant temps

hot water from a 140 degree tank will produce a lot less btu heating than 200 degree hot water, and iirc the relationship is
not linear.

point being, size everything according to what you expect to keep the storage coolant temp level at,  a 10kbtu exchanger is not going to
do you much good if it needs 200 degree water to deliver the rated btu's and you will be feeding it with 140 degree water.

bob g