Browse Forums Heating, Cooling & Insulation Re: Electric under-floating-floor heating 3Aug 25, 2014 2:43 pm Electric underfloor can be VERY expensive to run. Much cheaper to run hydronic (hot water) underfloor, or panels, heated by a gas boiler or heat pump (which will only use about a 1/3 the electricity of electric underfloor). However the up front costs for a hydronic system will be higher. Re: Electric under-floating-floor heating 4Aug 25, 2014 4:56 pm mcarthur Hmm... is there an obvious fault in my reasoning? For underfloor heating you have to heat up 10sq m x 70mm = 0.7cubic m of concrete before you can start heating up the air! (The over 1600kg of concrete is huge compared with the 31kg of air) The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Electric under-floating-floor heating 5Aug 25, 2014 9:39 pm ddarroch Electric underfloor can be VERY expensive to run. Much cheaper to run hydronic (hot water) underfloor, or panels, heated by a gas boiler or heat pump (which will only use about a 1/3 the electricity of electric underfloor). However the up front costs for a hydronic system will be higher. Thanks. That's what I was worried about. Can you run hydronic between the existing floor and a new floating floor? No nails may help? I can't see how though, unless I raise the floating floor above the existing one on bearers, but then I'm in trouble with the minimum 2.4m height in living areas rule? Re: Electric under-floating-floor heating 6Aug 25, 2014 9:49 pm bashworth mcarthur Hmm... is there an obvious fault in my reasoning? For underfloor heating you have to heat up 10sq m x 70mm = 0.7cubic m of concrete before you can start heating up the air! (The over 1600kg of concrete is huge compared with the 31kg of air) Ah, but the good part of my reno is that I'm not on concrete - I'm putting bamboo over an existing timber floor that's on bearers. So I'm not using concrete as thermal mass - hydronic - but rather radiant from electric and not using any thermal mass. I'd insulate between the bearers just to try help "push" the heat up into the room, and the heating sits on an insulating blanket that looks like foil which would help the radiant nature of the heat go upwards, so I'm hoping (!) that most of the heat truly goes into the bamboo and radiates into the air beyond. Of course there's a limit to how much one can heat bamboo, or any timber floor, but the manufacturer says about 25-27 degrees is fine. One question I need answered is how hot does the bamboo need to be so that the air temperature, at least at say head height, is acceptable (say 19)? Also, how hot will the feet be if the head is at 19? Re: Electric under-floating-floor heating 7Aug 26, 2014 3:11 pm I'm not too familiar with hydronic under timber. This site had a description, http://www.comfortheat.com.au/HydronicH ... imber.aspx Says they aim for 70M/sqm, would vary with location, house design & insulation levels. I've also read that the water must be around 30C, so you must be careful with timber choices, as it may warp. Re: Electric under-floating-floor heating 8Aug 26, 2014 6:50 pm ddarroch I'm not too familiar with hydronic under timber. This site had a description, http://www.comfortheat.com.au/HydronicH ... imber.aspx Says they aim for 70M/sqm, would vary with location, house design & insulation levels. I've also read that the water must be around 30C, so you must be careful with timber choices, as it may warp. Yes, that's one of the mob. It looks like I'll need to speak with some of the sellers and get the different opinions on electrical cost to heat, time to raise temperature, etc. If I get anything useful, I'll put it back into this thread for others to find later... Thank you everyone for reading! If anyone comes across more/new information, please add it... Re: Electric under-floating-floor heating 9Aug 27, 2014 11:36 am Mcarthur, For timber floors, there should be a floor temperature sensor that limits the timber temperature to 27deg C. That value is based on the timber flooring being quarter sawn, engineered timber with moisture content of 8%-10%. 70W/sqm is possible if the room temperature was set to 20deg C. In addition expansion joints within the slab should be extended to floor surface level and for any areas greater than 40sqm and between door ways an expansion joint profile is recommended. Mate, I do roughly 5 installs a month for retro-fit hydronic between timber joists. If you have access under your floor - that will save you having to rip the flooring out. But, if you are changing the timber flooring anyway, it makes sense to go hydronic. I recently removed electrical floor heating that was costing a customer $3000/quarter for a 200sqm home running on a timer for on average 3-4 hours per day. The heat output varies of electric systems between 150-200 W/m2 (but only in bathrooms!!!). For a 10mm timber board, my calculations (I'm a Mechanical Engineer) show heat outputs of roughly 100-120W/m2. I'd be glad to assist if required, feel free to give me a call. 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