Outdoor Wood Boiler with cast iron radiators?

nodesy

Hello,

I recently installed an outdoor wood boiler and plumbed it into several of my buildings including my home. For the house, I installed an air/water exchanger in the existing forced air plenum. In general, I dislike forced air systems and I am pondering going with radiant, specifically some nice cast iron radiators. Our house is very old and too tricky to try and do radiant floor. My questions are:

• Will cast iron radiators be more efficient than the forced air (when installed correctly), in general?
• I will be doing the installation myself. Are there any other major considerations or factors to consider that would make this project undesirable? System maintenance, etc?

Radiators are plentiful in this area and I really like the radiant heat and aesthetic of the cast radiators. Just don’t want to embark on the project especially if I will see a drop in efficiency.

any input is appreciated!

Eric

Jamie Hall

Radiators will work just fine. The BTUh output of a radiator varies wwith the water temperature, so you will want to consider that.

Otherwise piping and pumping the system is going to be pretty much the same as any other hydronic system. I realise that oxygen barrier PEX is very attratctive, but if you are inclined to use it make sure that you have some goof proof mechanism to avoid overheating it…

Ironman

You’ll need to use a sufficiently sized heat exchanger to isolate the house system from the unpressurized wood boiler. The actual heat load of the house will dictate the size of the heat exchanger needed.

An accurate heat loss calculation (Manual J or equivalent) is the first thing that should be done to determine how much heat is needed in each room. From that, the size of the radiators, piping, pump(s) can be determined.

Here’s a chart that will tell the actual heat output of a radiator based upon its surface area (EDR). Multiply that X 150 to get the BTU output @ 170* average water temperature.

hot_rod

The advantage of an air handler or forced air is very fast heat delivery. This is in part to the fact you are moving the fluid and also moving the air across the fins. Called forced convection.

So in a shop for example a forced air heat emitter will bring the air temperature up quickly.

For the most comfortable working shop I prefer the floor heat. It is comfortable, clean, quiet and stores a lot of heat.

In a radiant slab shop you can open the door, bring in a cold vehicle and within minutes the space will be warm as you stored heat in the weight, mass of the slab.

Radiant heat travels at the speed of light from warm objects, the floor, to the cold objects in the room.

I have done shops with both a unit heater for quick short use, melt off your truck for example, and the slab for a more consistent use.

Cast iron radiators move heat by radiant transfer and some convection with air moving through the sections.

leonz

https://forum.heatinghelp.com/discussion/200387/outdoor-wood-boiler-with-cast-iron-radiators

As brother Jamie has stated so eloquently radiators will work just fine.

Is your forest eater an open to atmosphere system or a closed pressurized system? If your forest eater is an open to atmosphere unit the system will add additional oxygen into the heating loop and cause oxidation in the piping and the radiators.

How much water does your wood boiler hold?

Radiators provide the end user with massive amounts of thermal mass coming from the cast iron or the steel they are made from as well as the hot water the enters them and leaves them to return to the boiler sump to be reheated.

Pex will be inadequate for this in delivering the heat produced from a forest eater as it will be affected by the heat generated and could very well weaken and melt.

A low high limit temperature of 140 degrees created by using a mixing valve connected to the cooler return water would work for this to create 140 degree water to deliver the heat energy to the radiators.

If you employ additional hot water storage that will only help you and create a much larger volume of water to use when creating a batch burn operation.

When I had my hand fed wood and coal boiler, I increased the amount of thermal mass greatly by filling it half full of standard fire brick. The full fire brick absorbed the heat from the fire and burned the smoke more effectively by radiating more heat in the fire box making it more efficient and reducing any creosote.

Adding full fire brick will only help you with making more useable heat energy and you will have less smoke as it will no longer be lost and wasted up the flue pipe.