bethelhousereno

It seems the turndown for ATAG is about 6kw. That's not particularly low so I'm thinking a viessman might be better for my needs. Unless I want to install a buffer between boiler and ufh manifold

We had planned 3 zones. One for rads and two for UFH (2 x 40m2 zone). The UFH area is quite openplan so I could be tempted to make this one large zone if it helped minimise short cycling.

Saying all that about ATAG, looking on their online manual they say the minimum output for the 36kw combi is 6.9kwh. That's a far cry from the 1:10 modulation ratio they suggested on the phone...

What thermostat system have you got installed? The installers are recommending a smart opentherm system so that the boiler output temp can be controlled. I'd much rather have a simple on/off type of system. I don't like relying on wifi for heating control and would rather keep things simple.

I put 150mm celotex under the main concrete slab (extension) and 200mm foam glass under the limecrete slabs (old cottage). so heat loss downwards shouldn't be too bad.

That's good to hear. The ATAG boilers claim to be one of the only boilers that have "bottom up" modulation too i.e. they fire up at a low output and work their way up from there, which should make them more efficient.

I'm having a real trouble deciding on boilers to install in my rennovation project. Gas combi boilers and underfloor heating - are they a suitable match? My ground floor has recently had 100mm concrete slabs put down with wet underfloor heating within them. about 80m2 in total and I spaced the pipe at around 150mm. First floor still has rads. It's a stone cottage that's been extended a couple of times. It's not the most energy efficient but te extensions have cavity insulated walls and double glazing. I am concerned that installing a combi might lead to short cycling of the boiler if the draw from the underfloor heating is lower than the minimum output of the boiler. I have read online that it is better to have a buffer tank in between boiler and UFH manifold but all of the Gas safe heating engineers I've had around don't think this is an issue. They all say combi will be fine. I am particularly drawn to ATAG's boilers which have a 10:1 modulation range, meaning a 35kw could range down to 3.5kw. I think... Can anyone offer some guidance? Am I worrying unnecessarily or is a buffer tank necessary in my situation? Thanks in advance!