Looking for the \" best\" mod/con---RAY, Prestige,Baxi

Jim_167

Looking to install gas mod/con boiler w/ Turbomax indirect in a 4 family house with combination medium size cast iron radiators ( 12 ) one zone and 3 zones of slant fin H/O baseboard, NO radiant.

Is mod/con worth the price over cast iron direct vent since is going to be operating at a higher temp for the base board?

Anyone have any feedback on the RAY mfg. by Mestek? I figured since its cast iron AND mod/con its the best of both worlds with little worry about failed heat x's, even @ $ 3900. The other choices were TT prestige, and Baxi with very limited US information.

Brad White_200

Operating Temperatures

Jim- hold up a second!

There isn't necessarily a need to run higher temperatures in baseboard compared to cast iron. Radiation output potential compared to a room's heat loss means everything. Nothing else, well, few things else, matter.

May I assume that the house and radiation is existing? Let me do so.

Firstly, Know Thine Heat Loss, room by room. Then know each of your radiator's output at a given common temperature, say 170 degrees average water temperature (AWT; 180F in and 160F out for example as a traditional rating point.

Now, if you have a room using baseboard and the heat loss is, oh, 6,000 BTUH. You have 16 feet of element worth 600 BTUH per LF at 170F average water temperatures. That is 9,600 BTUH worth of output. You can get your required 6,000 BTUH, on the coldest day no less, using 142 F. AWT.

If your other radiators are similarly sized, they can use the same water temperature and if more generous, even lower temperatures.

Point being, as you understand, the highest water temperature will govern. A temperature requirement for radiation which is ten or so degrees cooler than your highest (boiler) temperature, should have a mixing valve to tailor it to need.

With cast iron radiators, or all in general, Thermostatic Radiator Valves are recommended for fine-tuning. One might find that the entire house, all kinds of radiation, using constant circulation and outdoor reset will be quite comfortable with this setup. You just will not control the low limit of any one area as with conventional zoning.

The other aspect is outdoor reset. Even systems entirely sized for 180 F supply water with outdoor design temperatures at zero or the single digits, can still condense over 80 percent of the time if reset is used aggressively. Dr. Butcher at Brookhaven National Labs did a study confirming this.

Of the boilers you mention, the best one is the one sized best to your heat loss (not radiation potential). The biggest savings is in MODULATION less so than condensing. Too large a boiler and you could find yourself in cycle-city, not a good thing. Small and tight to the actual heat loss is a good thing.

Now, if this is a new house or renovation, which I doubt, you can size the radiation to all use the same water temperature day-one.