Hello, the mixing valve is set to 95F-100F for the supply water to our radiant floors. It is unusually cold here, currently -9F, and this temperature has been dropping the last few days (so this is the coldest it has been). The design temperature for our HVAC heating was 10F. Is it normal to have to raise the water temperature from the mixer when the temperature falls well below the design temperature? The radiant heat was keeping up until this morning. I have an app for the radiant controls and can watch the temperatures of all my zones and I am at the point where almost all my zones are calling for heat and the temperature of the zones who have called for heat the longest has dropped a degree further from the low temperature setting. Our buffer tank is set at 160F and we have a 110K BTU boiler (95%) so the amount of heat is not an issue, just delivering it during this unusual cold. I believe the heat loss on the house is around 60K btu but I would need to look up the manual J to confirm that. Thanks! Scott

Turn that baby UP!!!!! My one house (ICF) is running 110 deg F and maintaining temp, my other is 2x6 and is running 130 and not keeping up....live in Ann Arbor Michigan.

Yes, it sounds like you need a higher supply temperature for your current below design temperature conditions. As long as your heat source can provide more heat gain than the actual heat load, your HR system should be able to keep up. One normally uses a heat source that has outdoor temperature feedback (Outdoor Reset) which increases the HR system supply temperature as the outdoor temperature decreases. It sounds like you have an efficient HR emitter to be doing so well given your relatively low supply temperature at these outdoor temperatures. Why are you using oversized heat source, mixing valve and buffer tank? Were you having short cycle issues?

Yeah, I turned it up, lol, thanks for the feedback. The boiler is a condensing boiler and it heats a boiler buddy buffer tank. The floors and indirect water heater are supplied hot water from the buffer tank so I want the buffer tank water very hot for heating the DHW rapidly when needed. The floor water supply is mixed with the return water, normally to 95F but now increased to 118F as indicated on my gauges. My understanding is that the buffer tank allows the boiler to run less often and eliminate short cycling which appears to be the case as I see the system heating frequently and the boiler is not running. I have outdoor reset for the boiler via my controls but the floor mixing valve is manually adjusted.

The heat source oversize is for a couple of reasons: heating the interior floors (gypcrete 1.5" slab), DHW via indirect water heater and heating the garage floors (glycol heated via a heat exchanger, 4" concrete slabs). But, my understanding of HVAC is that cooling systems should be sized specifically to allow for proper run times and dehumidification. For heating I understand that oversizing is much less problematic. I am glad I have the extra BTUs right now.

Sounds good and you should be fine. Hope you see more normal temperatures soon and Happy New Year too!