OK, here’s what I have, I built this house in 95’when in-floor heat was all the rage in this area (Colorado Mountains). The system was thrown together with the basic conventional wisdom of so and so has this set up on his house and it works like a champ…. I know that’s bad. This setup has actually worked fairly well for 19 years but probably not very efficient. The dwelling is 3765sf total including 765sf attached garage. 2 story, slab on grade 1765sf (1000sf living, 765sf attached garage) lower walkout with IFC foundation walls, 2” rigid foam under 4” slab, 2 zones , 1 living, 7 loops@200Ft, 1 garage,5 loops@200ft and a 150 loop in the entryway manually controlled. All tubing ½” wirsbo on 8”IC. The upper main level, 2000sf, 2 zones, main living area,1000 sf, 7 loops@200ft 8”OC and Master Suite 1000sf, 5 loops@200ft wider OC than main living, all tubing on the upper level is in 1.5” lightweight concrete. The house has Corbond sprayed insulation giving it R20+walls and R50+ ceilings. I have completed many heat loss calculations using various programs and keep coming with around 108mbtu requirement using -20 for ODT. The current boiler is a Larrs Mini -therm II, running NG, rated at 186k btu/h (161.7k net I=B=R),(before altitude de-rating, 6700ft). That would make it way oversized than required which appears to happen a lot from what I can tell. 1 circulator (Grundfos 26-79F) I think that’s way too much pump) and 5 Honeywell zone valves (including DHW), There is a 80 Gal Amtrol WH-10 indirect water heater. I run programmable stats that basically fire the boiler from 1.5 to 2.5 hours in the early AM and the concrete and house stays warm without the boiler firing again until the next AM for say all but maybe 30 to 40 days in the winter or a DHW call. Piping was set up with a single circuit with a bypass per the Larrs IO manual. I experimented with the bypass early on and it seemed to get the best results with the bypass about ½ open. No matter where I adjusted the bypass I always ended up with a boiler DT of 11 degrees f no matter if 161 out and 150 in or 131 out and 120 back. It has been running 131 out and 120 in since installed. The Larrs ended up in bad spot the garage in order to provide for the vent which goes straight up through a upstairs closet and out the roof, I am recovering that space by going direct vent out the back wall with the wall hung modcon. I looked at the TT and there seems to be quite a few out there and the Lochinvar which seems to have more robust controls, liked them both. The Local supply house loves the NTI firetubes and claims they have the least amount of trouble with them(I’m sure their margins have nothing to do with their opinion) and doing a guts to guts comparison there was not a lot of stand out differences . I determined that a NTI TFT110 would be good even though my calculations indicate I could need as much as 108BTU, this TFT110 nets out at 99 (86 IBR). The NIT IO manual advises to De rate 12% at my elevation. The next size up puts me way over what’s needed and from what I can tell by reading on this site, I would be better off on the small side than the big side for efficiency’s sake. I felt that none of the heat loss calculators I used took into full account of my insulation Corbond + Fiberglass batt so the calculated 108mbtu requirement I think is on the high side . We have 300+ days of sunshine per year and I get good passive solar and have a Gas fireplace for the rare 1 time every 5 years it gets -20 a couple of days in a row. This house has always been warm due to the flywheel effect of the heated concrete, we have to open a door a lot even in the winter. I am convinced that I will be better off to stabilize the slab and house temps with a modcon maintaining 68 to 70 instead of bombing the heat and letting it cool off.
Here is the question, since I have already Hung and vented this NTI TFT110 on the back wall, the boiler is 10 pipe feet (7 ft horizontal and 3 ft up away from my manifolds and zone valves, I’m thinking I can create a primary loop from the new boiler to the existing piping and pump it with UPS 15-58, leave the zone valves where they are and pump the secondary with an Alpha 15-55 which in theory would increase flow if multiple zones call. I would run all the heating calls on low temp (130 max) and use another 15-58 pump for DHW at higher temp for my 80 Gal Amtrol and set it as priory. I anticipate there will be a need to tune the controls and maybe the piping, I’m just trying to assemble a starting set up. I have been keeping in mind Chris’s Universal hydronic formula of GPM=btu/hr / (delta T x 500) but I’m completely sure how to apply it to my situation.
I was an auto technician by trade, similar to HVAC, i.e we have to know mechanical, electrical and plumbing in our work. I built this house in 1995 and been remodeling and upgrading ever since. I considered letting a HVAC pro do this upgrade, but after getting a few quotes and listening to the wide range of opinions as to what boiler to use and how to set it up I could not find anybody that I was comfortable with. I am semi retired and have the time to mess with this and really enjoy the challenge. The professionals that contribute here are really appreciated and thank you in advance for any input.