Add radiant loop to gravity conversion

gsk3

Hi everyone,

First, thanks so much for The Wall. Dan’s books clued me in to this place, and I’ve learned so much here over the past year and a half I’ve been reading.

I’m a homeowner and at a point in knowledge and plumbing skills where I think I’m ready to take on a complex but non-critical project in the non-heating season: adding a radiant loop to my existing system.

The system is a Buderus G124 with Logamatic. Logamatic runs the circulator for a DHW pump directly, then there are two zones with Taco 00 circulatory and check valves, one which runs most of the house, and one which runs the baseboard fin tube in an enclosed porch. Those are controlled by 2 thermostats running into a Taco SR503, which has one zone unused.

Piping for the main house loop is an old gravity system that was converted to pumped (sealed expansion tank, pumping away, not P/S). Two parallel big mains run down basement with radiator piping taking off from those. Right after the micro bubble filter and expansion tank, there are T’s where the 3 current pumps connect, and a plug on the end of one—there’s room there to add but it would increase the head bump potential significantly and make it feel cramped,

The kitchen is cramped for space and has a woefully inadequate (about 26sq ft) radiator taking up some of that space. Consequently when it gets below 30, the kitchen is 20+ degrees below the rest of the house 🥶. We’re running an electric radiator in there and pumping another 1500W in all day (it’s below 20F outside) got the temp up to the low 60s with rest of house at 71 as requested on thermostat. There are a lot of heating losses in the kitchen as well, only some of which can be insulated better.

Fortunately the joists below the kitchen are easily accessed and run parallel to the kitchen, meaning with 9 joist bays worth of 15 foot long loops of PEX and AL fins and insulation I could heat the whole thing with radiant and make it really cozy.

My tentative plan (all advise/criticism welcome!) is:
- Tap in to the black iron 1 1/4” plug by the boiler with 1 1/4” street elbows and then convert with male NPT->crimp PEX fitting. Run a few feet of O2 barrier PEX 1 1/4” to a nearby wall I can mount plywood to.
- Hydraulic separator then mixing valve then pump then a small manifold gets mounted on wall
- Manifold is really for future proofing; has all outputs except one capped off. 

- 300’ loop of O2 barrier PEX or PEX-Al-PEX is insulated for 15’ run along ceiling to start of kitchen, then looped through bays, Al fins clicked over it, and back (insulated again) to return of manifold which connects via 1 1/4 PEX back to return into boiler,
- Control-wise, a new radiant-capable (floor sensor) thermostat gets mounted in kitchen, wired into the unused zone on the SR503. Pump control for that circuit goes straight to the new pump.
- I don’t believe I need a check valve or expansion tank on this loop (please call me an idiot and tell me if I’m wrong!)

Considering Caleffi 172 which gets me the separator/mixing valve/pump/manifold and other nice things like flow meter and control as well as zone valve options in the future if I add radiant zones (if this goes well I may do the whole first floor to reclaim space radiators are taking up).
Tekmar or similar for the thermostat.

What do you think? What am I missing?

Edit to add:
- Boiler seems to have plenty of capacity so I don’t think the extra circuit will tax it. Water temp of 160 on a 12 degree day (as cold as it ever gets) easily heats the house to 71F.

gsk3

Pics of 1) end of main loop, about where the kitchen is, and 2) 1 1/4” tee with plug I’d like to tap into. I have since tidied the insulation back up—it was pulled apart by the HVAC crew a year ago while looking for a leak.

gsk3

Would be a big help if someone sees this and thinks the plan is reasonable (or not) and left me a one line 👍 or 👎. Thanks for helping out a stranger!

Zman

What you are proposing sounds reasonable. There are little details like a check valve for the new loop, circ sizing, outdoor reset, pipe sizing (1 1/4" is pretty big and 300' loops are a bit long). and purge points to consider.
Posting a drawing of how you plan to pipe this will get you better comments. Conceptually this works.

gsk3

Thanks Zman. That’s really helpful to know I’m on the right track.

I can split it into 2x 200’. I assume the 300’ being too long is about resistance in 1/2” PEX being too high? 

I’ll work on a diagram so that items like check valve can get called out. I was assuming no check valve because it’s on same level as the boiler so no gravity circulation, but sounds like I need one.

I don’t understand why the outdoor reset matters for this loop? Logamatic runs one for the boiler as a whole. I assume the mixing valve for radiant circuit keeps a constant 110 or whatever?

EBEBRATT-Ed

@gsk3 I would split it into 3-4 shorter loops

Zman

You would need a check to prevent the other circs from pulling water backwards through the zone. You may have internal ones on the other circs.
I would split the loops if you can for more even heat.
I like outdoor reset because it prevents overheating the floor and space on warmer days. Opinions vary.

gsk3

Ah the zones balancing explanation makes so much sense, especially with the flow controls on the manifold.

Check also makes sense. The other zones all have check valves on them but I had assumed it was for gravity circulation, not to prevent each other.

Outdoor reset I still don’t get—the Tekmar thermostat has a floor sensor so between that controlling the pump and the mixing valve controlling the water temp I don’t see what outdoor reset would add or how it would be wired in. Boiler already has an outdoor reset and runs water temps of 110-125 until it gets below freezing outside. I’ll look more into outdoor resets for radiant loops so I can understand more.

Edit: Oh, I see. Like the Taco iSeries mixing valve with ODR? So that would run hotter water through the floor on cold days to get more radiation to the room if it needed it to get to temp?

Zman

Yes to the Iseries