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Originally Posted by MN Renovator
Don't get me wrong. I don't have much against radiant heat as a heat source. I'm not seeing your point about humidity or dust though.
Humidity control during a heating climate in a well sealed house is not needed but the most important part is that there is no difference between forced air and radiant heat in that respect. You don't remove or add moisture to the air in the enclosure with either method unless you install a humidifier or rehumidifier to the forced air system.
Dust control can't happen period without air movement, you need to pass the air through a filter to remove the dust. So I'm not sure where you were going with that either. Granted I'm not saying it's a big issue or anything, just trying to figure out where you were going there because a decent filter on a forced air system is going to clean the dust out of the air that passes through it. With the radiant system the dust will stay suspended in the air and precipitate out on surfaces and get kicked up by human activity. Either way you go it's probably better to avoid carpet versus making a decision over whether or not your heating system moves air.
With a low energy building you can centralize your heating and cooling and the entire structure will remain the same temperature. I've noticed that the further that temperatures deviate towards the outdoor temperature are the least insulated even to the point where I can block both return and supply vents from my most insulated room and have it warmer in that room than my least insulated room that has air flow. So you are right about not needing the hydronic floor plumbing everywhere if you are aiming for close to passive, or at least something around the R's of 5,10,20,40,60 with reduced glazing in the home design, although slab on grad you remove the R20 component and if going with R3ish energy star windows you'd need to reduce glazing to under 15% window to wall, IMHO. The only trouble you get into with that idea though is reduced ability to recover from large setbacks without either temperature differentials or long setback durations. I might be the only person with a 25 degree setback(for both away, sleeping, and often for entire 10 hour 4 day workweeks) though, oddly one that I'd probably want to keep even with a low energy building.
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Forced air does entrain the dust in the air far more than rads or floors do. It doesn't prevent dust from being produced but it does float around more which is why air cleaners are sold so much. You also notice the on/off periods which you don't with floor heating or cast iron/steel rads. Sound is also a lot more noticeable from a ducted system. Also, I can run a Grundfos alpha pump with 10w which is not possible with forced air.
The humidification issue is more to do with gas or oil burners that dry the air too much, which brings in the need for humidifiers of some sort. Of course this is less of an issue if an air handler is used off a low temp water supply. From a comfort point of view you need a higher minimum water temp to run an air handler than you do to heat a floor at the same outside conditions. I think the tighter the house the more we have to worry about excess humidity than adding it.
I would love to setback my house as much as you do but my spouse sometimes works from home and she is always cold so while I love the radiant heat, I won't get that level of control that warm air heat gives. I can live with that problem.
Drake wondered about my need to use a tank. If the control has a PID that looks at outdoor temp and/or humidity as well as indoor temps, the lowest water temps can be used to provide the heat and it can be designed to note when the passive is heating up the space at a fast rate. I use the floor tubing to distribute heat from over heated areas to less heated areas. I am all for multiple inputs to the tank but we have a hard time controlling the result with the tanks we have here. I wish we could get some of the European tanks but they don't meet our stupid pressure requirements.
But that is another topic.