I've noticed some advice here discouraging using a mixture of radiant floors and wall mounted radiators. I would love to know why that isn't the best idea. I am planning a house with a radiant slab on the first floor (no basement) and a framed second floor within the roof. I was originally thinking of just doing radiators (towel warmer in bathrooms) with individual controls to allow each room to be hotter or cooler to taste. Couldn't a mod con boiler handle each individual water temp separately as it's required. Thanks for your opinions!

multiple temps means you are running the mod/con less optimally and that you are increasing system cost and complexity with mixing hardware.

that said, depending on the water temp requirements, you might do them both single temp. but the radiators would have to be sized for the slab temperature requirements.

Finally, hydronic towel warmers for primary heat is ok... but I find them suboptimal for actually warming towels. You can't easily just turn them on when you want towels, and at low temps they heat up slowly to boot. If you actually want to warm towels, you should use electric units. If you just want a "towel warmer form factor" radiator, then so be it... but it would drive me nuts to stare at a "towel warmer" while I dried off with a cold towel.

NRT.Rob,

Thank you for your reply. Heat is my primary concern and not the luxury of warm towels....but, if i can have my cake and eat it too......!? Because of the design (second floor within the roof, lots of kneewalls) 'Warmboard' seems like a lot of unneeded upfront cost, and the other options seem suboptimal and expensive as well (I really don't like the idea of staple up). So, that's where the radiator thoughts came in...

Running low temp radiators would be fine if the numbers crunch. Seems much simpler to me.

I will be sending my house plans your way after the holidays for a more detailed opinion.

You may consider a platform system type application for your second floor, We distribute RHT floor panel system, but there are others as well, quick tracks for instance. A surface mount can run at the same temp as your slab, and will generaly be more efficent than the higher temps required for a staple up assuming you go the condensing boiler route.
Be sure you use a 2 inch rigid foam under your slab and along the perimeter vertical for best insulation value.
Dan

Thanks Dan,

I am planning to use 2 layers 2" xps (R20 total) under the living area slab, staggered joints and 2" in a garage/workshop area. Staple up just seems self-defeating in new construction, I've seen the RHT system on your website, and something like that is definitely a possibility over using radiators.
I'm curious if I will even need a mod con or if a dual use water heater would be sufficient. I'm planning to use the R32 quad lock on the first floor, R20 slab, roughly R25 framed second floor walls and R40 OCPU foamed roof. Serious Windows (SG9). The total heated area is under 2000 sf.

Sounds like a tight building,
first, I like RHT floor panel over a radiator system, out of sight... and you are that much closer to a non ferrous system, RHT floor panel next to a staple up your delivered water temperatures can be considerably lower, same as the slab temp simplifying the system design.
next, mixed use water heater?? not my favorite choice but arguably effective with the right load, I do not recommend an open loop system so consider a TACO x block or the idea of pump/ heat exchanger/pump. this will isolate the heating fluids from the potable.
Dan