Indoor wood boiler to on demand radiant floor

kritch114

First time poster but have found myself on this site countless times over the years so I figured it’s time to sign up. Anyways although not typically recommended I have a on demand water heater heating my 3,000 sqft house and 1,400 sqft garage and working awesome. I knew this would only be a backup when installed and now it’s time to hook up the wood boiler. However having the water heater I don’t have any mixing valves for my loops. My question is how can I use a mixing valve on my loop coming from my wood boiler if a good portion of the time I won’t have a heat usage. Taking 180 water from the boiler, sending it to the house at 120 and it returning pretty close to the same temp I’m not understanding how that works. Any help would be great thanks

Kaos

Simplest is a 4 way mix valve that can do both mix down the 180f to your floor heat and mix up on the return so the wood boiler doesn't get the 100F return.

You can do the same thing with two regular thermostatic mix valves.

hot_rod

what size indoor boiler? What is the total heat load?

Do you have a buffer tank?

kritch114

125,000btu conventional wood boiler. I was considering a small buffer tank for a hydraulic separator.