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Discussion Starter #1
I built this earthberm house three y/a. Heat is via wood burning gasification furnace with in-slab hydronics.

The furnace is computer controlled via a conventional thermostat.....The firebox smolders wood under hypoxic conditions until the thermostat switches "on." Then a fan blows a little air (oxygen) in and the H2/CH3 + O2 burns in a nice blue flame down in the lower combustion chamber, heating the water....There's an internal thermostat that regulates a pump, sending the heated water to a holding tank, and an external pump that circulates the hot water thru the house.

The furnace is continually heating the water even when the furnace is "off" and the furnace pump periodically sends heated water to the tank based on computer settings....The general circulation pump, however, only circulates hot water thru the house when the thermostat is switched "on."

The Problem-- the house is so well insulated that once the set temp is reached and the thermostat switches "off" it takes 4 hrs or more for the ambient temp to fall enough (1degF) to switch the thermostat back "on."...In that extended period, the concrete slab cools off enough that it takes a good deal of wood to bring that large thermal mass back up.....

...Even tho the furnace is smoldering away making a good deal of heat continually, it remans tied up in the tank, not being circulated....I've found this week that by manually messing with the thermostat every hour, I can turn the furnace on for 10 or 15 minutes, keep the slab warm and the house really warm while burning 25% less wood.

Any ideas on how to automate this process electrically/electronically?
 

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Add a Time Delay Relay in parallel to power your circulation pump. The relay can cycle the pump on and off automatically.

While the relay is operating, the thermostat can still call for more heat, turning on the boiler and circulation pump.

The types of industrial relays are described here: Understanding Time Delay Relay Functions
 

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Discussion Starter #4
1800 sq ft house with 975 sf garage/utility area, divided int 6 rooms...would need minimum of 3 elect heaters running to adequately heat it.- probably cost in the neighborhood of $10 +/d...I only use one cord of wood/month .

Thermostat in floor wouldn't work-- floor is main heat sink, so furnace would be running too much that way.

I don;t know much about electricity/wiring...I need a timer that would control the general circulation pump, but that pump is apparently wired in series with the furnace computer & pump. The timer would have to bypass the computer, but still respond to it when called upon.
 

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Discussion Starter #5
Add a Time Delay Relay in parallel to power your circulation pump. The relay can cycle the pump on and off automatically.

While the relay is operating, the thermostat can still call for more heat, turning on the boiler and circulation pump.

The types of industrial relays are described here: Understanding Time Delay Relay Functions
WE may be on to something here, but my eyes gloss over and get that 1000m stare when I read stuff like that. They should take the "Understanding" part out of that title.:)

Thanks, but which one do I need? I want the one pump to run for 10 minutes every hour PLUS whenever the thermostat says it should run.
 

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Add a Time Delay Relay in parallel to power your circulation pump. The relay can cycle the pump on and off automatically.

While the relay is operating, the thermostat can still call for more heat, turning on the boiler and circulation pump.

The types of industrial relays are described here: Understanding Time Delay Relay Functions
This is the best option in my opinion. Just circulate some more water through your slab on a timer. You will need to be able to tweak that timer to find the sweet spot
 

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Sounds like you have a fairly sophisticated system with a computer control. IMHO a timer on your slab circulator would work but you would need to tweak it depending on outside temperature. A better solution would be to automatically adjust your slab temperature according to outside temp. (I don't understand your comment about your slab being a heat sink and therefor not a good place for a thermostat.) Keeping your slab "warmer" would reduce the lag time in the system. Many modern thermostats take into account outside temperature and adjust for that.

It might be worth a chat with the folks that installed the system - maybe they can adjust the computer settings.
 

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Open a window
 

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Discussion Starter #10
Thanks for all the replies....I know the solution-- a timer on the circulating pump that keeps some hot water moving thru for 10 minutes every hour just to keep the slab from cooling off too much, regardless of the inside air temp...What I don't know is how/where to connect it without disabling the normal switching process from the furnace controls.
 

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I am not an HVAC specialist nor do I play one on TV so this may be hogwash. The pump comes on whenever it is supplied with electricity. It doesn't know or care where the electricity comes from. Assuming it runs on 120 volts you can hook up a second source of electricity, like plugging into a wall outlet or hard wiring one, and put a timer in the line. Hook up both the computer controlled source of electricity and the new timer controlled source to the pump. The pump will come on whenever it gets electricity from either source.

Be certain that both sources of electricity are on the same leg of the electrical service that come into your house. If you don't know how to do this get a knowledgeable neighbor or electrician to help.
 
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