Infloor heating


Old 11-06-12, 05:01 PM
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Infloor heating

Not sure if this is the right forum or not, but here we go. Put infloor heating into my garage. Just using a 50 gallon hwt. Four loops each around 280', with R-10 blanket under slab. Poorly insulated walls so far. I have a 60 degree temp difference. Out at 160 and back around 100. I know I am running the tank to hot but am afraid to turn down as i don't think it will keep up. Was thinking my pump was too slow. Have the heat link maifold flow control to 1gpm. Any thoughts. Thanks !
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Old 11-06-12, 05:38 PM
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With a 60 deg differential, you are delivering mucho heat to the floor. What, exactly, is your problem? With just in-floor heating, it may not be practical to heat your whole garage? What temp do you want to maintain in the garage, and at what outdoor temp? Around here, garages are heated only to help start cars (really not required) or having a shop in the garage.
Old 11-07-12, 12:58 PM
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What was the flow specification in the design of the system? At 1 gpm through 4 loops of 280 feet, that would be roughly one quart of water per minute through 280 feet of pipe. Viscerally, that rate of flow sounds low. 280 feet of 3/4 inch pipe would hold 300 quarts of water. So the change would be 1/300 of the volume per minute.

My shop is heated with hydronic heat in the floor, but has R13 walls and R 49 attic insulation. I don't know how fast my pump runs, but it is rated over 20 gpm.

My system has not run since before dawn, so I cannot check the inlet and outlet temperatures for you. My water heater is set under 140 degrees.

Since you are moving heat to warm a concrete slab, it seems that faster movement of the water would enable heating the slab faster. The thermostat would then turn the pump off until needed again.

If the water is faster and entering at 140 and returning close to that, your expense in heating the water would be reduced per unit volume, although the cost may be higher to run the pump faster.

Unlike forced air heating, hydronic systems heat a large mass and maintain it rather than heating low mass air. My system usually runs only once per day by thermostat.

I would consider increasing the rate of flow of the water through the system.

If it is a commercially designed system, referring to the original specifications might help. Otherwise and all other things being equal, running it at 15 gpm might be worth a trial.

I think my hydronic system is wonderful for heating my shop. I hope you find a solution to your dilemma.

Old 11-07-12, 07:14 PM
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First off a concrete slab should never see more than 140f water temperature due to the fact it may cause the concrete to crack.
Second to get more heat you want to speed up the water and reduce the delta-T. Most radiant systems were designed around 15f delta-T. I do not know what the heat loss for your garage is but radiant will normally give a max of about 30 btu's per sq. ft.
Old 11-09-12, 08:10 PM
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I would consider increasing the rate of flow of the water through the system.
Me too. Why are you only running 1 GPM ?

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