Question on Heating capacity with no heating upstairs

[Blynchy]

After reading a number of posts on this forum, it has convinced me to go with UFH downstairs only with cabling left for electric rads upstairs. I'll probably put in electric loops into the toilets and ensuite. I have a question regarding the spacing of the UFH pipes.

 

The calculated heat loss for my house is 3kW for the ground floor and 1.7kW for the first floor. Should I space my underfloor heating pipes on the ground floor to accommodate 3kW or 4.7kW or somewhere in between. My plan is to set up two zones with a manifold for each as the house is an "L" shaped house with one side being single storey and the other being two storey. The single storey element accounts for 1.8kW of heat loss. Thanks for your help

[JohnMo]

I would size for the whole heat loss.  You can always decrease flow temp to down rate the system.

 

The thing with UFH loop spacing, is the closer the spacing the lower the mean flow temp for a given W/m2.  Also closer spacing results in more pipe and more water in the floor.  Which may move you away from any buffer requirements. 

 

My heating requirements are 3.1kW on a -5 deg day.  But I have 192m2 of UFH at 300mm spacing.  My mean design flow temp is 26 degC.  A spacing of 150mm would have dropped the mean flow temp to 24 degC.  The loops are in 100mm concrete.  The system response is slow.

 

Down side of wide spacing is a slow reaction time, if you want on off timers, go for a close spacing.

 

It the W/m2 that is the criteria you need to post.