how low can you go?

[sweetheat]

People with storage tanks, how low is to low for a 806 gallon storage tank feeding a 28X42 slab on grade radiant system? My zone is set for 100 degree water. I've had storage tank temps at 86 and 91 recently. My thermostat is set for 64, It never gets below 64. Tank seems to bounce right back to 180. With the warmer days I've sometimes gone more than 2 days without a fire. I noticed stack temps above 600, as I may have to clean my boiler tubes soon. Is their a thread on what to take apart and how to clean your boiler tubes? thanks sweetheat

 

[NHFarmer]

There are a couple of threads on cleaning the tubes.They are very easy to clean.Takes about 30 min. or so. Just open the top cover closest the flue,remove the wing-nuts,remove the smoke chamber cover and brush out the tubes.I use an old shop-vac and drop the suction down the tubes after I brush them.Just watch out for any live coals.

 

[in hot water]

As low as you can go and still satisfiy the heat load. A radiant slab will put out about 2 BTU/ square foot for every degree difference between ambient air and slab surface temperature.

For example a room temperature of 64, slab surface of 74 would be 20 btu/ square foot. That output may be enough on mild days, even some cold days. A supply temperature of 90F or less to the floor would probably be fine for that condition.

A heatload calculation will define what supply temperatures you need to maintain temperature on a design day. Anytime it is warmer than design, you could get by with lower supply temperature. the rule of thumb above would help determine that temperature requirement.

An outdoor reset control watches outdoor temperature and adjusts the supply temperature to the floor, to always heat the space with the lowest possible supply temperature.

A great method is to run the tank up to 180, and allow a reset control to adjust the supply temperature to the radiant. That allows you to leverage the most amount of heat from your storage on any given day.

As the weather warms I don't run my tank as hot, I may back the setpoint to 160F this time of year. That way I burn less wood, have less standby loss and can still get through the night on the 500 gallon.

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