[Greenbuilding] Type of concrete for radiant floor

[Shawna Henderson]

Steve and all,

 Don't let this wig you out:

>The down  
>side is that the lower I set the temp, the longer the boiler runs to  
>get the zones up to the thermostat setting.
>

Here's why:

When you had your temp setting way high, the boiler ran for short 
periods, but overheated the slab (and consequently, the air temp). As a 
result, your thermostats read that the air temp was adequate for much 
longer than the floor was being heated. You then ended up with a 
'bounce' effect, where the slab temp was overheated/underheated, in 
effect 'short cycling' your boiler, which reduces the lifespan of the 
equipment. So, although your boiler's running longer now, it's probably 
not running as often because you've got a better balance of supply (ie, 
lower floor temp) and demand (ie, thermostat readings). You might even 
notice a reduction in fuel use.

If you don't already have an outdoor temperature sensor, I would suggest 
adding one in if your system controller has the capacity to read it. A 
'smart' control reads inside and outside temp and then adjusts the 
delivery rate and temp of the water to match the load demand. Maximizes 
efficiency of system, reducing energy use.

Tekmar is the make of 'smart' control that I have had good success with. 
Modulating controls are more expensive, but, IMHO, the benefits in terms 
of longevity of the system and reduction in energy costs compensate.