Residence (mine), mod-con boiler, 2 zones Zone 1 (main zone) is converted gravity, cast iron, heating most of the downstairs and all of the upstairs. Second (smaller) zone is RFH under tile, covers kitchen and adjacent small addition. Open floor plan so these rooms do get some heat from zone 1. Each zone has a thermostat and a Taco SR501 relay. No mixing from the boiler, runs between 110 - 135 F. Three pumps on the system: a return pump upstream of the boiler, one pump for radiator loop, one pump for RFH loop. No outdoor reset (I know ...). Overall happy with this system, in our second winter now, got lots of help here along the way. :thumbup::thumbup: When the RFH is calling but the rads aren't, the boiler tends to short cycle because the RFH gpm draw is low, so boiler quickly overshoots temp and shuts down. But RFH loop keeps calling, so that soon the temp in the primary loop drops and the boiler cycles again. Most often happens because the RFH is calling to up the slab temp, not because room temp is low. To help minimize that short cycling I want to try running the RFH loop whenever the rads are running, to boost the floor temp up in that zone when the boiler is already running (and condensing), but also maintain the ability for the RFH to call and run separately from its own stat. I expect this will boost the floor temps higher than we have them now but that is OK and I want to try it out. So, current setup: Main stat calls ==> boiler called, pump for radiator loop kicks in Addition (RFH) stat calls ==> boiler called, pump runs for RFH loop desired setup: Main stat calls ==> boiler called, pumps run on both loops Addition (RFH) stat calls ==> boiler called, only RFH loop pump runs (as before) How to do it? Can I do this with existing relays? I considered taking the RFH pump off its relay and running it from the orange wire on the boiler, but then would the RFH pump continue to run when the boiler is called but temp is already up? I'm thinking no, but I dunno ... Sorry for the long post. Current controls diagrammed in images, p2 is "radiator pump" and p3 is "RFH pump." [IMG]http://2albatross.dyndns.org/EV%20items/boiler/boiler%20wiring%20822%20Brookridge.ppt-1.jpg[/IMG] [IMG]http://2albatross.dyndns.org/EV%20items/boiler/060801VolbrechtFinal.pdf%20%28page%203%20of%203%29-1.jpg[/IMG]

Firstly, I have to say THANKS to all the regulars on this forum. I've been reading for days and days, trying to educate myself as much as possible. Today I registered to ask some q's. It's going to be a long 1st post - trying to get it all in here... Intro: [LIST=1] [*]I'm in Milwaukee, WI. Design temp: -4 deg F [*]1400 sq ft 1.5 story bungalow. Built 1924. [*]Wall composition: Brick exterior, air space, sheathing, stud framing, lathe, plaster. I'd say about 1/3 of the exterior walls are insulated - only what we can reach from inside the attic. [*]LOTS of windows: 29 single pane double-hungs w/high quality storms. I've rebuilt and re-weatherstripped all sashes. We're keeping them for charm - the uppers have orig leaded panes. [*]Cast iron radiators on 1st and 2nd floors. [/LIST] Existing boiler: natural gas Burnham "Series 2" 205 From the data plate:[LIST=1] [*]Mfg Date: 1983 [*]DOE Htg Cap: 107,000 BTU/hr [*]Net IBR: 93,000 BTU/hr [*]AGA Input: 130,000 BTU/hr [/LIST] Burnham says their current 205 is 80% AFUE ... I doubt my 26 year-old is still that efficient, if it ever was. I'm guessing the house was originally steam. The piping is gigantic, and has reducers to mate with our existing boiler. I DIY'd a heat loss calulation using the Build it Solar online calculator. I *think* what these calculators want is 1) surface area having unconditioned space on the other side, and 2) the R-value of these surface assemblies. My combined 1st & 2nd floor heat loss came to about 113,000 BT/hr. Since I don't know what's inside some of my walls & ceilings, I estimated low on R-value for those assemblies. Like many home owners, I'm interested in the federal and state tax incentives for the purchase of high-efficiency heating and DHW-heating systems. Though they're both old, my existing boiler and hot water heater are working fine. But, if I replace them now I get $1500 back. If I wait for them to die there may not be such incentives. I do not expect new appliances to ever "pay for themselves" in reduced heating costs. But new appliances *should* make the house more sell-able than 20+ year-old equipment, when we need to sell it (within the next 5 years). Additionally - and this is what started this dream/project - our chimney is disintegrating and leaks slightly into our attic. I've got it temporary patched together, but it's a time bomb. Our current boiler and water heater vent into the chimney. Instead of paying for a chimney rebuild, I'd rather replace the boiler and water heater with direct-vent appliances and just remove the chimney. I recently got a quote for a Buderus GB142/45 + indirect DHW system. It was more expensive than I was expecting, though not un-affordable. After reading a lot it seems the Buderus is a very high quality boiler, and the quote was fair. However, I question the /45 model sizing. The dealer measured the dimensions of our radiators - which, from reading this site, is not the correct sizing method. Did not do a heat loss calc. Our current 80% (at best) efficient boiler is a 130k BTU/hr input boiler. Does moving to a 92%+ efficient 160k BTU/hr boiler make any sense? I would have thought we've move to a lower input boiler... Maybe the extra because of the indirect DHW? Also, based on lots of reading here, I'm starting to question the aluminium mod/cons. It seems like too much is left to the installer's ability, and I'm extremely risk-averse! I'm waiting to hear back from TT on who installs them in the MKE area. I'm certainly more comfortable with stainless. But, honestly, I'm thinking a nice cast iron boiler might just be in my future instead of a mod/con. I'm looking closely at the Burnham Revolution and Weil-Mclain GV. I'm going to call around for quotes on the Revolution and GV. I'll ask for rates on a pro heat-loss calc as well. Anything I should be considering that I'm not? Again - THANKS for such an awesome resource!