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Author Topic: In slab design  (Read 1987 times)

reggart

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In slab design
« on: October 27, 2018, 09:51:56 AM »

I wanted to reduce the temperature of my in slab loop using a 3way mixing valve.   In the furnace installation guide it showes two circulator pumps in a primary/secondary configuration.  This is a normal configuration and is generally required to protect a standard boiler from thermal shock. I was wondering if that is really required on a heatmaster?  My thoughts are that the boiler has a large holding tank and a circulator pumps dedicated to mixing the water inside the boiler. It seems highly unlikely that any thermal shock would be happening with this setup.  I didn’t want to setup my boiler in a primary secondary configuration unless absolutely necessary.

Also how are you guys controlling your in slab heat?
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RSI

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Re: In slab design
« Reply #1 on: October 27, 2018, 09:34:57 PM »

The main reason that is done is because the pump for the floor heat turns on and off with the thermostat to to control the temperature. If you do not have a primary loop then the flow will stop completely when you turn off the floor heat.

Even if there is no other use for the boiler water besides the floor heat, with it not flowing it could freeze when idling.
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wreckit87

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Re: In slab design
« Reply #2 on: October 28, 2018, 09:55:23 AM »

Not to mention, the flow rate through the floor loops is very minimal and the return water from the floor will only be 70-80 degrees, and shock the hell out of the stove. Ideally you should have a plate heat exchanger separating the floor loops from the boiler loop, so the boiler loop runs constantly always keeping the plate hot. Then the floor side would have a mixing valve,air separator, relief valve, expansion tank, etc with its own pump that only runs on call for heat
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E Yoder

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Re: In slab design
« Reply #3 on: October 29, 2018, 02:51:17 AM »

I've done a few jobs where the in floor pump pulled through the mixing valve all the way in from the stove. It was downhill to the slab, otherwise might have cavitated.
Never worried about shocking the OWB tho, there were other pumps running mixing the water jacket, which may or may not be the case in this situation. Was more difficult to purge air out and in a colder climate (I'm in VA) I would be concerned about freezing the underground lines as was mentioned.
I'm not saying that it is the best way, but it can be done in some situations. Some it just wouldn't work.
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