RE: "Ideal boiler temp"..I was concerned about Legionaires someone said 55f=degree (c) +

Sorry Jonr,

jbaron got me all stirred up.

Convection is a factor in radiant floors at typical design temperatures but not as great as was presumed in early studies. The latest calculates closer to 30% at design temperatures.

As the design water temperature for a SIP in S.Cal is probably very close to ambient convection is probably negligible. I see many using the "cold floors" argument against radiant floor heating for SIP and ICF construction but the fact remains that when there is a load the floors are not cold and the condensing boiler is operating at 98% thermal efficiency.

Most unheated floor temperature can be measured in the the mid-sixties when room and outdoor temperatures are below 70°. This is a cold floor to the bare foot.

Comfort is the absence of discomfort and warm floors are a luxury. An ERV may help create a beneficial load if applied with in conjunction with ODR.

Badger:

Good points..I left out ..we do have an ERV .This house is amazing the SIPs keep it at 70 deg +/- 1 without anthing on unless the dip is <50 or >100 degrees ambient... We wanted to do Geo pumping but our city wanted $$$ ofor permits and a few months to drag our inspections and approval= (Their definition of green is charging exorbadant fees - KleptoBurerocrats!)

It is easy to get boilers and domestic water heaters mixed up. Even more confusing when a condensing boiler coupled with an indirect water heater is one of the best domestic water heaters available.

Though I believe the hazards associated with Legionella are for the most part exaggerated for self-promotion (a subject in which I have some familiarity) I set my combination water/space heaters at 140°F and mix the radiant design temperature down from this accepted "safe" water storage temperature.

At least one foreign and one domestic condensing boiler company offer boilers with indirect water heaters that have a sanitation mode, which raises the indirect DHW tank temperature to a minimum temperature for a minimum time limit. A nice feature, but as indirects are very well insulated and the boilers very efficient, savings from this feature are negligible.

I do believe, Legionella is a considerable threat to the elderly and the infirm.

I feel your pain...on the permit issue.

Gov't. should facilitate, not procrastinate.

I think there may be a general misunderstanding of the appliance you have, Laars Mascot?
The heating loop Primary loop is isolated from the domestic water.
You have a condensing appliance, you can run the heating side "cold" 90 degrees, your fuel efficency will increase the colder you run the appliance, and it may help keep the slab at a 'not cold" state longer as it will not be subject to the steeper swings in temp.
As to the domestic side, the side arm tank you have should have a heat exchanger internal if the system is proper. You can set the domestic at 120 or 145 from the boiler controls. This is separate from the heating. with higher stored water temps I would suggest a 3 way mix valve on the domestic H20 outlet.
When there is a call for hot water the boiler will ramp up and direct all its energy to the potable side arm tank only. When the hot water tank is satisfied the boiler will ramp down the to the heating loop temp and be fully condensing.
You are not heating out of the hot water tank.
Dan

Posted By John in the OC on 29 Dec 2010 01:07 PM
The Thermostats are LuxPro (1 seems defective) the boiler is a Laars Mascot HT1.330 and reseve tank

The LuxPro series T-stats aren't very appropriate for most radiant floors (could be used for low-temp panel radiators though), and WHOLLY inappropriate for slab radiant systems due the inability to compensate for the lag-time issues of high mass radiation.  SFAIK all LuxPros are set up to operate with a hysteresis around a setpoint, and expect a highly responsive heating/radiation.  T-stats that sense at least rate of rising/falling temperatures (to a fraction of a degree), and anticipate the setpoint will tend to work better.  It's probably worthwhile spending a few bucks on the appropriate T-stat, even though that won't much affect how warm the floor feels during light & variable heat load conditions.  With the right T-stat you'll maintain more even room temps, and you'll have less of an over/undershoot when conditions change quickly, as when a weather front moves through.

I skimmed the thread, didn't see if you specified the type of radiant floor you have (only that it was designed by a web-vendor.) But the fundamentals outlined by others is true: If you don't have a significant heat load, the floors will never FEEL warm, even while heating the space.  They shouldn't ever feel  ICE COLD, but it might only be a degree F or so above the room temp under low heat loads.  You can still  get that warm cozy floor in a house & climate where the heat loads are NEVER very substantial by designing it for radiant only under part of the floor (spots where you might sit or lie on the floor would be more appropriate than under beds, etc.).  That raises the water & floor temp requirements for meeting the load, but allows you to sit/stand/lie where the temps are most comfortable for you.  This approach isn't well suited to design-by-web-forum or generic web-vendor designs though.

Dana's idea is an interesting one. I, for example, have three loops in my heated concrete, and I could easily stop or truncate some of the flow out of one of the loops, though I'd have to be careful about which one to be sure that it wasn't the one near the slab sensor. I'm lucky in that my loops follow a fairly serpentine pattern. You might be able to do the same, if you have more than one loop.

In the same vein, you could also insulate or cover some of the floor with carpeting or area rugs. That would then raise your water temperature requirements a bit, and lower your efficiency a bit, but it would then require the remainder of the floor to be warmer to provide proper heating. It might not have too much of an effect, but if you are looking for a degree or two, it might provide enough of a bump for you.

Jeff

We have a heating demand year around, it can snow in July. For a very well insulated house even here underfloor radiant is overkill as the demand is so low.

Great feedback, thanks!
Dana:
RE: "The LuxPro series T-stats aren't very appropriate" any work around suggestions?

Posted By John in the OC on 04 Jan 2011 10:18 AM
Great feedback, thanks!
Dana:
RE: "The LuxPro series T-stats aren't very appropriate" any work around suggestions?

Is this a slab, or is tubing between floor joists? (If below the floor, does it have heat spreader plates? Suspended-tube? Stapled-up in contact with the floor but un-plated?)

Is it 140 degrees F to kill legionella?

140F does kill legionella, and is behind many local code requirements for setting hot water tanks to a minimum of 140F. (Some codes call out 120F min. though, a temp at which legionella colonies won't grow, but won't necessarily die off once established.)