AboutMorgan M. Audetat Expertise Radiant floor heating. Snow Melting. Boilers. Indirect water heaters. Tankless water heaters. Current owner BadgerBoilerService.com Minneapolis based mechanical contractor specializing in Mod/Con based, integrated heating systems. System design, consulting and technical training world-wide.
Currently designing hot water based heating and snowmelting systems for spaces ranging from 50 to 50m square feet. Consulting fees start at $500.00US
Experience 30 years. Organizations: Charter Board Member - Radiant Panel Association, former manufacturer of the first American-made wall-hung, sealed combustion condensing boilers, son and apprentice of mechanical & plumbing contractor.
Continuing Education: Uponor/Wirsbo advanced design school 2007, Power Limited License (low voltage controls) 40 CE credits 2005, B&G Little Red School House 1993, Tekmar Controls residential and commercial 1993, Division Manager and Advanced Hydronic Seminar Host for the first Hydronic Radiant Floor Distributor in the USA 1990, Hydronic Heating Association Workshop participant with Richard c. Bourne, PE spring 1988, Master Plumbing/Hydronic/Solar Course Red Rocks Community College 1987.
Education: B.S. University WI 1981, 26 yrs. continuing education.
Licensed CO, MN & WI. Home Inspection license WI exp.
Awards and Honors: My momma's favorite son.
Past/Present Clients: References upon request.
Expert: Morgan M. Audetat Date: 4/5/2008 Subject: Tankless water heaters and Radiant Floors
Question Hello
I'm building a new 1800sq ft home in Waldport, Oregon and I'm wondering if a Rinnai tankless water heater is a good way to go?
Answer This is a common though questionable application. I design many systems using various conventional and non-conventional water heaters. However, the thermal efficiency (the amount of fuel consumed in the combustion process) of a tank-less or low-mass water heater such as the Rannai, Bosch, Takagi or Noritz is very close, if not identical to the old-fashioned tank type water heater.
The tank-less water heater gains operating efficiency (how much fuel is actually used to perform an assigned task) by not having to maintain a standing load of hot water.
As a primary heat source then, low-efficiency water heaters (thermal efficiency less than 88% of any style are not my first choice for structures located in climates that see sub-freezing temperatures for more than a few weeks.
Given the size of your home, your climate and the lack of integration in most tank-less applications, I wouldn’t consider it.
Mod/Con with integrated indirect water heater will give you operating efficiencies at least 20% above your proposed application.
I would also consider and often specify Bradford White's NEW Combi-Cor water heater. In this one package you have small footprint, 82% efficiency and a built-in separation of heating and potable (drinking) water. Though the thermal efficiency is not great, its output and integration give it an edge on smaller heat loads where domestic water is needed.
The Combi-Cor has a double -heat transfer- wall between the potable and heating sides of the water heater, which adds to the cost, slightly diminishes heat transfer efficiency and adds nothing to the imagined cross-contamination risk. In a couple of odd (read silly) municipalities this double-wall heat exchanger is actually required. But overall I give the Combi-Cor a B- if properly applied.
One should not however confuse double-wall heat exchanger with the co-mingling of potable water with heat transfer water. Whereas the first practice adds unnecessary cost to a perfectly safe system, the latter invites disaster. DO NOT drive heated water through a radiant floor system and then proceed to use the same water to serve plumbing fixtures of any kind.
