There is no way hot water heat could be a fire hazard. It is much less than the temperature of boiling water! Even the most flammable of gasoline soaked carpets would have to be around 500f to ignite. We have hydronic heat under regular maple hardwood (15 year old system) and it is zero problem. Your mileage may vary depending on your system, but think of it this way -- the water under our floor is like max 100f (the floor only gets up to 80f), and our house gets close to 100f on the hottest of sunny days (no AC up here in Canada although I came close to the breaking point this summer). So I can't really see how the heating is more harmful to the floors than everyday life. Slightly related: my uncle was chiding me for the 'safety hazard' of letting my curtains drape over my hot water radiators. I was like 'What are they going to do, slightly warm my curtains to death like a gentle beam of sunlight?' Well, I was more polite in person. But seriously. This post was edited by robotropolis on Mon, Nov 25, 13 at 22:41

RCMJR & misoilman, tnx for your replies. RCMJR: LDJ appears to have been in business since 1999. According to the LDJ website they claim the boiler is "Great for radiant floor heat systems". I'd be interested in talking to existing users to see how they are getting on with the the system. I took a closer look at their page about the corn boiler and they claim it's thermostat controlled, perhaps it's able to be dialed down. The picture of it looks like a water heater with a hopper sitting next to it. I'll post the url for the corn boiler. The capacity of the water heater portion is eighteen gallons. They also have an option that would allow the boiler to provide hot water for "domestic" use. So would be able to heat water for shower's, washing dishes etc. Right now the utility room has two gas fired water heaters sitting in it, one for the floor heat and one for domestic use, I think. We'd have to talk the heating and plumbing guy that took over from the H&P guy that had been maintaining the system for many years. The retired fellow is still in town and we might be able to talk him into coming over and orienting us with the systems. misoilman: Having the seller comfirm the moisture content of the corn would be the first thing I would insist on when purchasing the corn. I do know from talking with the folks at the elevator, they will not accept corn that is more than 15 percent moisture. I also need to check with the city to make sure there isn't an ordinance that would preclude me from having a small gravity box sitting next to the carport. If the gravity box is small enough, I'd even consider backing it into the carport. Alas, there is no basement on this dream house. Just a thick concrete slab...:-) So We'll probably use a couple of five gallon buckets for transfer of fuel from the box to the hopper. I'd just consider it a form of exercise...:) We're also a bit concerned about the age of the plumbing in the floor as it is original to the house. The impression I got from the house inspector was that the in floor plumbing was put in place then had the concrete poured over it. I'm going to have to have someone that has better eyes than me and know's what they're looking for, look at the blueprints and see if we can find out how thick the concrete is. Luckily, we've secured a "home warranty" from the seller for at least the first year (at their expense), and there is a possibility of extending it through the second year. I should also probably state that the corn boiler is not a done deal as we are still in the early part of the research stage. Although, a friend of ours has suggested we check the website of the Governor of Illinois and see if there are any grants or other incentives that we might be elgible for. Governor Blagojevich (Bla-goy-a-vich, what a mouthful) is very interested in promoting alternative fuels and energy use in Illinois. Here is a link that might be useful: LDJ's Corn Boiler page

Your HVAC expert who is designing the system should explain the requirements that the manufacturer has for their particular system. In general, in your situation, you will need lower temperature loops closer together rather than the traditional higher temperature loops further apart. The whole system has to be designed for the water temperature that you will need, as well as the PEX placement distance. Floor coverings also has to be taken into account in the plan. Rubber and carpet actually have insulative power (R values), and are not conductive to easily passing the heat through into the home. That has to be calculated when designing the system, and it will increase the lag time to temperature changes, which is already radiant's biggest drawback.

Since you have chosen warmboard over gypcrete, what was your reasoning behind it besides responsiveness? I am sorry for the confusion. I didn't build a house with Warmboard, I had it in a house where original owner had installed it. It wasn't a house I built. I used it in the sense that I heated the house with it. I looked at the Gypcrete system and somehow feels uneasy about it. Doing a concrete pour over first and second floor does not sound structurally sound to me. Gypcrete has positives and negatives but shouldn't be overlooked because of structurally sound. I think a competent and knowledgeable designer is much more important than which type of system you use. So if you don't have a lot of experienced local people, you have to find experienced people who can help design at a distance. I would start with Radiant Engineering (talk to many companies though). A long somewhat unbiased discussion of radiant: First, it should be noted that radiant heat isn't an efficiency discussion. As people have pointed out many times hydronic radiant systems rarely have a positive payback. They are simply too expensive to install and they never payback if you are installing central air. However, every decision in your house isn't about payback. There are many decisions, such as paint color, cabinet color, cabinet design, many fixtures, etc., that are about your enjoyment of your home. No one has a pool installed because they want it to add value to their house. Radiant fits soundly into that category. Next: A discussion of trade-offs between the different systems. It is important to note that ALL radiant floor systems will provide a comfortable environment to a home that other heating methods struggle to achieve. There are basically five considerations in radiant heat (1) installation costs, (2) operating costs, (3) responsiveness (4) allowable customization and (5) noise (as hot water passes through cold aluminum plates it makes noise). If we look at the different systems we can typically see how they handle each of these things. Warmboard is (1) very expensive to install, (2) it has a low operating cost as it is a warm water system rather than a hot water system, (3) incredibly responsive for radiant heat (able to heat a structure in hours rather than days), (4) low customization and (5) low noise. Underfloor transfer plate systems are (1) moderately expensive to install, (2) low operating costs as they are also warm rather than hot water systems, (3) are somewhat responsive (4) highly customizable and (5) have more expansion noise. Gypcrete overpour is (1) moderately expensive (still cheaper than the two above), (2) have low costs as,they too are warm water systems, (3) not responsive at all, (4) are highly customizable and (5) eliminate almost all noise. Staple up systems are (1) pretty cheap (2) high operating costs as they are a hot water system, (3) not responsive at all, (4) limited customization (they are more limited by physics than design), and (5) are pretty noisy. So looking at Warmboard vs. similar systems - the only real concern from using any aluminum covered plywood system is the noise. Warmboard eliminates expansion noise because of the "special" glue they use to adhere the aluminum to the wood. I can't really tell you how special their glue is, I feel confident they will say super special and their competition will disagree. Warmboard type systems vs. underfloor transfer plate systems - Warmboard is quieter but the loops are not really customizable. Loops are 8" apart with Warmboard, so you can choose not to put warmboard in places but you can't get the loops closer together. With transfer plate systems you can customize the heat of a room by simply moving the loops closer together. This means that you can make the floor right outside the shower warmer than the floor beside the toilet (not many people spend a lot of time standing beside their toilet), but there is more expansion noise. Warmboard is a bit more responsive than transfer plates. Warmboard vs, gypcrete overpour - Gypcrete overpour gives you almost unlimited customization without the noise associated with aluminum transfer plate systems. However, it is not at all responsive. Staple up systems - They are more expensive to operate than any of the above systems but are cheaper to install and easier to maintain. You are not likely to nail through a staple up system with a nice thick transfer plate. Also easier to remodel with staple up systems. TL:DR In the end, if I was ranking a radiant system today - I would probably rank it - underfloor transfer plates > gypcrete > Warmboard. But it is a three way photo finish so it wouldn't take a lot to change the order. Also noisy houses don't bother me at all.