Wood boilers / heat exchangers - steam pressure?

[samsquatch]

I'm considering a hydroponic system to heat a home. Before we talk about professionally installed systems - which I will likely use anyway due to safety - I'd like to discuss the opportunities of using a heat exchanger custom molded & attached to the side of a standard woodstove, or fireplace insert, as more of a DIY approach. I know near nothing about floor heating at this point, and I'm trying to learn as much as I can before exploring that option. OTOH I am an avid DIYer.
Actually my first question is a simple one. I do not understand how hydroponic systems aren't constantly boiling and steaming all over the place. Take an example (and please know that I am a complete beginner when it comes to this stuff):

1. Start with a cold floor. You arrive home & you turn the thermostat up (which starts the boiler or you start a fire in the stove)
2. The pump turns on and begins circulating as the water is warming
3. Water is warmed and heat transfer to my tile floors begins warming my smiling wife's feet
4. Room temperature matches thermostat. When this happens, what does the system do? Does the pump stop circulating hot water? But there's still a fire in the firebox, right? So the water in those pipes is heating very rapidly and is no longer being radiated in the floor, in my puny brain this is going to create steam and will trip the pressure relief.

Or, where does all that heat go?

Cheers

 

[maple1]

Depends on the system and what is making heat. Generally speaking, there are controls to slow the fire when the unit gets to a certain temp (stopping a fan or closing a draft door), and also those to dump excess heat somewhere should things progress past that.

 

[peakbagger]

My friend has a homebrew system consisting of a Fisher type stove with home built hat exchanger that sit over the fire box. It made of parallel lengths of slant fin connected by pipe bends on each end. This sits directly on top of his stove with some solid patio blocks on top of it to make sure the fins are in contact with the stove. He has a temperature switch on the discharge of the coil that turns on a circulator pump. It ties into household radiators. If the system goes over a high set point he sends the heat to a fan forced unit heater in corner of his basement. On the rare chance he loses power he has a pressure relief valve and a couple of valves and unions on the coil. If he needs to he just moves the patio blocks and moves the coil away from the stove and uses it like a normal stove. He had been heating the house this way for close to 30 years.

Bad things happen if you generate steam with a system not designed for it. Every pound of steam has a lot of hidden energy in it and if it gets out it can do a lot of damage.

 

[E Yoder]

Most wood boilers have some water volume to absorb some heat too. Very different setup.