No heat exchanger for wood boiler

BigMacWisconsin

Hi Everyone,

I've been in a house where I acquired a wood boiler for 4 winters now. I've been super interested in how to get more out of it and make it more efficient. I've already replaced the old crappy piping and put in ThermoPex, but an issue I've run into is I have to adjust the water temperature on the outdoor wood boiler almost daily to prevent the house from getting too hot on sunny days and make sure it can keep up on cold days. 

One thing I noticed right away is the inside radiant system is the same loop as the wood boiler. So basically the water pumped from the boiler goes into the house directly into the zones. So the pressure from the pump on the boiler is enough to circulate water through the house when the thermostat isn't calling on the zone circ pumps. 

Looking online more, is see a lot of installations use a heat exchanger to separate the systems. Does anyone else have a system with an outdoor wood boiler that circulates the same water from the wood boiler to the zones in the house? My goal is to be able to regulate the temperature in the house better, but don't know what to expect with a wood boiler.

Thanks in advance!

hot_rod

Is the OWF a pressurized type? What type of heat emitters?
The home should have a thermostat to regulate heat regardless of what the OWF is doing?
Some pics or sketches of the piping might help determine what you have.

BigMacWisconsin

The OWF is not pressurized. 2 zones in the house are baseboard radiant, the 3rd which was likely added on later is in floor.

I tried to capture the flow a bit in the pictures, but the problem I run into is the radiators get hot even if the thermostat isn't calling for heat. The natural flow from the main circ pump on the OWF slowly pushes the hot water through the whole house. 

In the bottom picture, the pex pipe on the far right is the hot from the OWF. In the top pictures show zone 1 and zone 2 going to the different floors of the house. I didn't detail out the 3rd zone because that one is even more screwy. Blue arrow is showing the return to the OWF. 

Recall I moved into the house in this state and have no background in this other than being interested in playing around with these things as I'm an engineer. 

BigMacWisconsin

I just drew this up too, hope this helps. 

GroundUp

Simply put, yes that system needs a heat exchanger to operate properly- the entire indoor system should be pressurized. Your OWB should always be at 170* or above at cut-out, any less will result in excessive creosote and oxidation. What make/model is the OWB?

BigMacWisconsin

Thanks, that's what I was wondering. Looks like a fun project for next summer. I've got a woodmaster 4400. 

hot_rod

A number of things could be better. I'd pipe the boilers parallel to one another. Repipe with circulators on the supply, pumping away from the expansion tank.
Or a single delta P circulator and 3 zone valves.

Some piping options here.

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_10_NA_Hydronics for wood-fired heat sources.pdf

BigMacWisconsin

Thanks for the tip, that exact piping drawing is what I found that made me think I might benefit from piping in an exchanger. I want to do what's right and get the most benefit while not disrupting everything and completely redoing it. Thanks for all the help, I'll read through more of that and see what I want to do next summer. 

hot_rod

And if you want to learn more about how HX works, and accurate sizing. Even a long hand formula

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_29_NA_Heat exchangers in hydronic and plumbing systems.pdf

Download one of the sizing programs to play around with HX options.