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Radiant Floor Heating/Radiant floor - saving cost without sacrificing quality



We are about to start building a house in the Bay Area and have to cut cost by reducing some of the concrete and steel.

The initial design included radiant  concrete floors on both levels (hydronic / on-demand gas boiler). Slab on grade on the 1st floor, and 3" topping slab on the 2nd floor.

The Bay Area doesn't get too cold but it doesn't get very warm either except during Sept/Oct. On the flip side, August can be quite chilly. Overall, it's pretty mild year round.

The biggest change with the cost cutting exercise was switch to a wood floor on the 2nd floor. By reducing the dead load of the second floor, we're able to replace all steel beams with wood beams.

Another cost saving measure was to pay a minimal upcharge for architectural grade joists and leave them exposed; ie, no ceiling. But this means we're also eliminating under-sheathing insulation since the sheathing becomes the ceiling.

Which brings me to the radiant floor questions:

1) Can we have a radiant upper floor without insulation on the underside of the sheathing? Won't the excess just radiate back down onto the usable space below? Use panels that reflect the heat back up, like Warmboard (which can also double as the floor sheathing), or other less expensive alternatives?

2) The master bedroom is above the kitchen, the master bath over the dining, the home office is a mezzanine open to & overlooking the double height living room and the guestroom is above an unheated, but super insulated, garage. The lower level is an open plan with the central living space open to the home office above.

3) Without insulated floors, would the radiant heat from the slab on grade be enough to warm the spaces above? The open mezzanine would be the most obvious place, but how about the master bedroom and master bath? The guestroom will most definitely need some sort of heat source, but since it's not used very often and the wood floor isn't as cold as a concrete floor, can we use radiant wall panels tied to the hydronic system?

4) Although we are not building to Passive standards, we will have R28 walls, an R30 flat roof and triple glazing throughout since we'll have full height lift & slides on the 1st floor.

I'm not against doing the radiant on the 2nd floor, but omitting some or all of it could save us a decent amount, and this is a relatively temperate area.

It would be interesting to hear your more experience based and scientific reaction to my potentially flawed logic.

Looking forward to hearing what you have to say.

Badger Boiler personal radiator
Badger Boiler personal  
Slab-on-ground radiant floors will heat one level, double-high quite nicely. In temperate climates you may be quite comfortable in a loft or mezzanine and you may not. You have to have a heat load and look at adjacent window etc. to predict "comfort".

I would need to know the floor coverings for the proposed radiant floor panels.

You may use a European panel radiator for door isolate rooms on the second level and I occasionally place a panel or a radiant wall next to an office desk, since we can get chilly sitting at our computers now can't we?

For the ultimate control of micro-zones, like your personal office radiator, I find a condensing storage water heater is ideal. Far from the wasteful atmospheric storage water heaters we grew up with, a condensing water heater, sans the chimney, can exceed the operating efficiency of a condensing boiler when loads are modest or zones are small. They are also very well insulated and afford the luxury of filling a large bath. The EPA recommends bathing with a friend to save energy...not really.

I designed a retrofit radiant floor for a client in the Bay Area a couple of years ago. As I recall they had no insulation in the walls and little in the ceiling and still a combi water heater was more than sufficient. If your particular construction and heat loads fall into the condensing water heater design parameters, you will save money on installation, operation and living space.

For more detailed answers you will have to send me a drawing.  

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Morgan M. Audetat


Radiant panel heating design, including floors and ceilings, European wall panels and snow melting for residential and light commercial buildings..............................................................-Master of Steam and Hot Water,City of Minneapolis....................................................--- Master Plumber, State of Minnesota...........


30 years..... Charter Board Member - Radiant Panel Association, former manufacturer of condensing boilers, former national distributor of radiant floor products, son and apprentice of mechanical & plumbing contractor. Current mechanical/plumbing contractor specializing in hydronic based, integrated HVAC systems. Radiant floor heating/cooling. Snow Melting. Condensing Boilers. Indirect water heaters. System design, consulting and technical training world-wide. Licensed contractor, designer, installer and consultant.

B.S. University WI 1981 CONTINUING EDUCATION: Viessmann Condensing boiler and Solar water heating certification 2010, N.D.S.U. Lead Worker RRP certification 2010, Knight condensing boiler certification 2009, Wrightsoft Manual J CAD certification 2009, RPA Designer & Installer Certification 2008, Nate Hydronic/Forced Air Certification 2008, Uponor/Wirsbo advanced design school certification 2007, Buderus Wall-hung certification 2007, Power Limited License (low voltage controls) 40 CE credits 2005, Basic Hydronic Certification IPEX & Northern Alberta Institute of Technology 1998, Charter Board Member - Radiant Panel Association 1994, Residential Off-Electric to Hydronic Conversion Heating School Canadian Hydronics Council 1994, B&G Little Red School House 1993, Rood Utilities (now Auburn Technical Institute) Oil Burner School 1993 ,Tekmar Controls residential and commercial 1993, Division Manager and Advanced Hydronic Seminar Instructor for the first Exclusively Hydronic Radiant Floor Distributor in the USA 1990, Hydronic Radiant Heating Association Workshop participant with Richard c. Bourne, PE spring 1988, Master Plumbing, Hydronic, Solar Course Red Rocks Community College 1987.

Awards and Honors
2009 System Showcase Award - Radiant Panel Association

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