Diverting vs mixing valve for radiant floor slab

barnesville

I have a radiant slab basement floor in my new house with one 5 port manifold but no mixing or diverting valve. It works well but I've been studying heating systems and am curious if a one manifold system needs a mixing valve or diverting valve to increase efficiency? it's a very basic system; boiler set to 90F, spirovent valve, expansion tank, pump, manifold, and autofill valve.

dko

What boiler are you using

GGross

A mixing valve is beneficial or needed when the supply temperature to your system exceeds what is required for a given loop or zone. In your case if you are using a condensing boiler (high efficient) and do not have a high temperature heating zone attached to the same boiler as the low temperature zone, then you do not need a mixing valve and would not notice any benefits to adding one, but would be adding an additional point of failure. in floor heating systems (and most hydronic systems) do benefit from an outdoor reset heating curve, which modulates the supply temperature up/down based on outdoor temperature. In some applications the boiler may not be capable of doing this on its own and you may see an external mixing valve and control that modulates the supply temperature. Generally it is very uncommon for a boiler to not come with outdoor reset option these days. If you are unsure about any of this then please post a picture of your system as it is installed.

barnesville

Thank you for the detailed response. there is a sensor outside and the boiler is electric set at 90F. Unfortunately, our electric rates are the highest in the state so I am looking for a way to cut heating costs other than having a cold basement.

hot_rod

Does your utility offer off peak rates? is so a buffer tank that starts charging at 7:00 PM could carry you through the high peak rates.

The building dictates the amount of energy, if you have done everything reasonable to get the load as low as possible, ten it comes down to how efficiently you can use the fuel. Lowest possible SWT is one option.

Up front cost is high, but at those low operating temperatures you would be over a 2 COP with a A2WHP, even below 0 conditions.

barnesville

It's an Electro-Boiler unit

GroundUp

The only thing a mixing valve does is reduce the supply temperature. Your BTU requirements will not change, meaning the electric usage would not change either. It probably doesn't help that the system is piped with non-barrier PEX and that the flow rate is much too low for that boiler, so if that were corrected you may be able to squeeze a little more efficiency out of it. That unit requires .3 GPM per KW so assuming that's either a 12 or 15kw boiler, it needs a minimum of 3.6 GPM and it appears that you have two zones at only 1 loop each which will never flow even 1 GPM.