Radiant floor for large great room

NoCoAztec

Fantastic forum.... I've been on so many construction/energy sites for years and only found this one now.

We're building a new house (framing now), in coastal Southern Cal. Climate is mild but it's chronically cool. Often chilly/breezy. Everyone underestimates how cool the weather actually is for 9 months of the year.

The building will be tight. HVAC will be via ASHPs, ducted. Our great room is large, around 1000 sq ft, on the second floor, and the ceiling ranges from 9' to 12'. There will be 17' and 10' wide glass doors. Like many buildings crammed to fit under a height limit, we have significant ducting challenges, and I am skeptical that the great room will receive enough warm air, or put another way, that it will get enough air distributed around.

This has me thinking about using radiant floor for the primary heat in there, under the subfloor, maybe using Radiantec with their aluminum plates/reflective barrier, and a combo-boiler (we're already planning on gas on-demand DHW). Subfloor is 1.125" Advantech, and the flooring will be .75" engineered wood. I'd run all the tubing now, and if we're as chilly as I fear, then we plumb up to the boiler.

Does this sound like a reasonable approach? We have a great HVAC engineer, and know our heat loads, etc., but they don't do radiant. So I'm looking for feedback before I go doing something silly....

MikeL_2

   I suggest a product like Viega climate panel. Finished flooring goes directly on top.
   I'd also use outdoor reset, constant circulation, and an operating system with an adjustable heating curve;  the Viega hydronic mixing block is my favorite - no tstat needed.
    

STEVEusaPA

Radiant floor, radiant ceiling, or depending on the design, exposed round spiral duct may work.
As much as I like radiant, just for 1000 sqft, don’t know if I’m putting in a boiler for a micro zone.
If he’s in your area, here’s the guy you’ll want…
@Alan (California Radiant) Forbes

NoCoAztec

MikeL, Viega looks great. We already have our Advantech framed it, so that ship sailed. Only way now is to run it under the subfloor. I hadn't heard of an outdoor reset -- great idea.

Steve, the boiler would be the on-demand water heater. The price diff between a standard heater and the combination boiler is hardy anything. It's all the other stuff that adds up! California Radiant is Nor Cal, ~400 miles away. :-(

hot_rod

A load calc for that room would be a good start. Sounds like you want a floor warming system to assist the forced air in the rest of the home

HVACNUT

NoCoAztec said:

Steve, the boiler would be the on-demand water heater. The price diff between a standard heater and the combination boiler is hardy anything. It's all the other stuff that adds up! California Radiant is Nor Cal, ~400 miles away. :-(

How do you go about piping a heat zone off an on demand water heater that's also being used for DHW?

Mad Dog_2

Think about the Bradford White Combi Cor 
Which is a normal sized/footprint water heater tank that has a coil you can do quite a bit of radiant off of.  I've used these with great success.  Speak with an the engineers and tech support at Brad White for load performance realities before you go any further.  Mad Dog 🐕 

GroundUp

STEVEusaPA said:

Radiant floor, radiant ceiling, or depending on the design, exposed round spiral duct may work.
As much as I like radiant, just for 1000 sqft, don’t know if I’m putting in a boiler for a micro zone.
If he’s in your area, here’s the guy you’ll want…
@Alan (California Radiant) Forbes

Since when is 1000 sq ft a "micro zone"? He wants a tankless anyway, and the cost of a combi boiler is marginally higher than a tankless. That "micro zone" will easily accept double the low fire BTU output of any combi boiler

Paul Pollets

Electric radiant cabling works well if you're under 1000sf. The cable must be embedded in a min of 1" drypak mortar or gypsum. It's a 240v system.

Tim_D

Plates are the way to go but be sure to use the extruded aluminum type.

NoCoAztec

Circling back on this, the heat load for the space above is 7000 btu/hr.

hot_rod

That is a pretty small load for even a small combi. If you want to go with plates under the subfloor a small electric or gas fired tank could work.

That load number is on a design day, most times it will be a portion of that.

At the very least install the tube, decide on heat source later.

Smitdy

How many kitchens' and baths are you planning feeding off that combi boiler? They are ussually not good for more than 1 kitchen/1 bath. I always use a stainless indirect with my installs.  I like the new HTP (Ariston) boilers and I've been using the superstore indirects for a long time. If it is a microzone consider using a buffer tank or use the HTP Pioneer( it holds 60 gallons of water). - good luck with your project!