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Circulator pump too fast? Lot's of info

The_teacher Member Posts: 8
edited November 2019 in Radiant Heating
Hi all, I've been lurking this forum for the last year. Thanks for all the info. I've spent a lot of time on different forum and I can say they help a lot.

I live in New Brunswick Canada (close to Main and just over the pond from the U.K.) We get cold long winters. -20 C (-4F) plus windchill in normal in December, January and February

We bought a house (bungalow) 38' x 60' with a 30' x 30' attached garage. So the basement is 38' x 60' as well.

The garage and the space under (30' x 30' X2) is not heated. (cold room and fire wood storage)

House was built in 1996 with 2x6 framing with a 8 ft foundation. House is really well insulated with being all outside brick walls. There's currently around 10'' of blown insulation in the attic (Will be adding an other 8'' soon). No leaking windows... Last year we ''heated'' the house with a 15000 btu heat pump up top and a wood stove (good for 3000 sq ft) in the basement. I say ''heated'' because we we're still cold (64f) in some area of rooms.

House has radiant infloor heating with slab. Main floor has 1.5-2.0 inches of slab and basement in unknowed (probably 4'' or even more). Dont know if its insulated on the bottom. Garage and under has been drained and isolated.

So the house was running with wood boiler, but I replaced with a propane boiler from NTI (FTV150C) combi model 95% eff. CO2 is set to 10.4% at max and 9.6% at min modulation. Modulation ration in 10:1 so the lowest input is 15 000 BTU's. Running open manifolds, no zone actuators. Flow have been set to regulated temperature in each room. Not ideal but seems to works good. Bedroom are about 65-66F, living room kitchen bathrom are around 67-68 F (this is all air temps). Slab is usually 1-2F max warmer than air.

Current setpoint at 0 f is 93F output. ODR seems to work fine. It was 28 F this morning and 84F water was comming out the boiler. I dont have any overshooting problems. I use a Honeywell/Aube TH135-01B non programmable thermostat. I have it set for 68F and its running classic mode with anticipation. Boiler may run for 3 hours at a time every 20 hours or so...

This boiler condensates like crazy. Dripping really fast. Almost a stream.

So before I ask some questions, here are some guide points.

I'm not after a 24/7 hot slab. We wear slippers and love touching each other with cold feet Hahaha. I see this system as one big radiator, not toasty warm feet machine. But I would like certains time of day to have warmer feet. Like wake-up time and supper?? time (5pm). I'm looking for maximum $$ saving and warmth when I need it.

Boiler- NTI 150C with combi DHW
Piping is primary/secondary loop. Boiler has internal pump and secondary loop is run by Armstromg astro 280CI at 167 W (this is one of my concerns)
Boiler piping in 1'' cooper to the manifolds.
Pex looks to be 1/2 I.D. but I have to double check.
Pex Spacing next to windows is probably 6'' (it runs hotter) and middle of room is probably 12''
System runs at 15 PSI.
First floor is running 7 zones and loop are between 200-300ft
basement is setup with 7 zones (same lenth) but I'm only running 2 zones (rooms with doors) because it was costing me way too much propane.
System has been flushed with Fernox F3 and added fernox F1 treatment.
Open manifolds (no zone actuators)

So this morning the boiler was heating at 84F and water return temps was 78 in no time. Over the course of the heating cycle, the return temp rises and so does the output temps (I think boiler wants to achieve delta T of 8f and more). If I set the pump on speed 2 (its currently on speed 1) the return temps seems to rise faster than speed 1. Even to the point where it exceeds the heat curve set points. (with speed 2...)


Is that circulator pump too fast? (Armstromg astro 280CI at 167 W)
I'm aiming for long run times between heat need. 2-4 hours twice a day. (I'll adapt run time... not raise water temps manually

I have an other pump on hand B&G SSF-22 at 92W

QUESTION 2: I would like to have heat when I need it.

I'm not after a nightly set back (the house is too well insulated anyways) All I want is heat when I want it, not in the middle of the night as the temps drop below thermostat set point.

So would the honeywell/aube TH140-28 work?

I know I could use a slab sensor, but I would have to chip my concrete and the thermostat is in the middle of the living room. The only was I would use a slab sensor would be in combination with air temps sensor. But I'm sticking with air temp thermostat for now. Like I said, not looking for warm feet 24/7.

For exemple:

Start heating at 3AM to 6AM (warm feet(69-70F) for wakeup) probably set thermostat at 75F (It will never reach 75 but the floor will be warmer. Air temps will rise to 67-68F

Leave for work and sunshine does is magic. I would set minimum air temp at 67F

Start back heating(set at 75F) around 3 PM until 6 PM. Warm feet (69-70F). air temps should be close to 70 with the sunshine of the day plus the heated slab releasing it's energy during the day. Temps should drop slowly during the night.

All of this with the ODR to regulate water temps.

So basically, I'm aiming for a heating schedual instead of it being temperature based.

I know I will have to modify the start and stop time a few times a year but I do not mind.

I'm thinking this schedule would offset the "sunshine setback" of daytime sun heat.

I'm not a plumber, hvac nor a radiant specialist. I'm a shop teacher. I teach welding, machining, electricity and small engine. But I read, read and read. I ask questions and find answers.

I have gotten this far. Just looking for heat at good times during the day and $$ savings.

I have done all the plumping, wiring etc.

If you havn't notice, I'm french. So my writing is not the best.

I have included a lot of information. More can be included if needed.

No I have not had a heat lost analysis. But everything is already running...

Hope this post is not too long.


EDIT: my propane comsumption is still around 5 gallon of propane/day. 475 000 BTU's /day for around 2800-3000 sq ft. That's 6.59-7.07 BTU/ sqft/hr


  • hot_rod
    hot_rod Member Posts: 16,289
    Heating systems need to be dynamic, as then load on the building changes minute by minute. The system will need some feedback from the thermostat to prevent over or under-heating.

    Slab radiant, being a high mass distribution does not lend itself to setback operation. Ideally ODR, thermostats with slab sensing, and take the time to dial in themODR curve. You could get to a near constant circulation system where the boiler ramps up and down close to the load.

    A heat load always help with boiler sizing. How did you select the 150 size?

    You need to know more about the loop size and length and piping to assure you have the right circulator. Is it a multi speed?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    edited November 2019
    I understand what you would like to do. The hurdle is as pointed out high mass radiant. It just doesn’t lend itself well to forced temperature swings. Mass is slow to heat up, and Cool down. It takes hours, and not minutes.

    It sounds to me your radiant is functioning as designed. The system delta is dynamic. With a delta of 6 degrees you could slow pumping a little. It’s the animal of perfect circulator sizing.

    As it stands I would say your system is as efficient as it gets. You will spend as much heating up, and cooling down than maintaining temp. As you pointed out yourself set backs just don’t work. What you would like to do is localised setbacks.

    To achieve this you would have to implement some zoning. Which is doable.
  • Gordy
    Gordy Member Posts: 9,514
    You noted propane usage. Your domestic hot water, and any other propane appliances are in that total number.

    You have a combo boiler so it’s making your DHW also.

    Usage means little with out knowing your outdoor temps, or degree days for that period.
  • The_teacher
    The_teacher Member Posts: 8
    edited December 2019
    Size of 150 btu was to have the combi option. Calculation was based on 25 btu/sqft for a design day. No real heat lost was made. Design days might see 16 btu's at the most and I'm feeling out the system. But I wanted the combi system... we have big 60 gallon water heater (electric) that we rent from out electric company. So I want to scrap that... we dont use much hot water...

    When I wrote this it was before the first "3-4 days cold snap" we had(-1 F). Before the cold snap, I was experiencing the "shoulder season" I think its called. Slab heats up, and cools down before air temp changes. Return water was 71 and would rise to 75 and finish around 80-82F. Must of been hard on propane..

    Floors were at 68-69all day long with air temps around 68 (15000 heat pump puffing once in a while). I bet I did not use 1 cup of propane more than I did while in 20-30F wheater... with more run time, return temps are higher (starts at 80 and finishes at 85-87F when t-stat is satisfied) and the blower RPM is running way lower (20000 btu vs 40000 btu during 20-30F weather)

    I Switch circ pump. Less noise, less waste but pretty much the same speed. Cant go wrong. Only has 9 loops of 250-300 ft of 1/2 pex. I calculated the head lost and both pumps are close at the given intersection of the curve.

    Water output is at 91F and is juste perfect.

    The little th-135 non programmable hydronic is really good with its anticipation. When it calls for heat it adds .6C so that the air temps only needs to raise 0.5C before it cuts out. At 91F at useally end up at 19.2C. Take around 1.5 hours before you feel warm feet and 3hours for the air to reach t-stat set temp of 19C(67F). With the sunshine its perfect.

    But here is why the programmable t-stat would comme in handy...

    When it was 4 pm, we had a beatifull sunny day of -1F. Hydronic didnt come on from 9am until 4pm (when I turned it on). I could tell the sun was fading and the slab has given its heat(floor was at 66-67. So I turned it on from 4pm until 5 pm (20000 - 30000 btu's in put). Around 5:30PM out feet were warm and the air was still warm(68F) now at 10:15PM (t-stat says 67F) as well as floor temps.

    So I want the t -stat to make it start like I did... a few hours before real heat demands... So the temps swings im after are aroud 1-2F at the most. Ill report my propane usage in a bit. It was 5 gallon with 20F Wheater. Well see how it is with -1F.

    Btw its the only applice using propane.

    I also bought 100 bags of attic cellose insulation. Currently have 10-12" and adding 8-10" more. R50+.


  • The_teacher
    The_teacher Member Posts: 8
  • Gordy
    Gordy Member Posts: 9,514
    Nice kitty cat :)
  • The_teacher
    The_teacher Member Posts: 8
    > @Gordy said:
    > Nice kitty cat :)

    Hahah just did the top end en 'er. Has 0.2 miles on it haha. Also did and AGLT mod to it... so wide I have to reverse in truck bed haha. 46" center to center wide ski stance
  • The_teacher
    The_teacher Member Posts: 8
    Just notice my primary pump 15-78 was on speed 3 (130-140 watts). Probably to be safe that it would handle the 190f for fan coils... but for my low temp radiant system (91f set point) speed 1 (80w) is good enough. Return temps went down 3F and condensate starting pissing in the drain. Flue temps went down 2f also. Blower rpm when from 3000 to 2700. Basicaly a 6000 btu reduction. Crazy the amount of condensate it produces.. a 5 gallon bucket is not even an option lol.


    Btw propane usage hs droped from 2% to 1%. It updates everyday. Cant tell in 1 day (temps and sun was the same) that it helps... depends on tank update time of day. Its not a 50% saving thats for sure lol
  • The_teacher
    The_teacher Member Posts: 8
    Since switch the primary pump to speed #1 delta t are now almost start at 20 and finish around 15. House heats fine. Blower rpm is still 300 rpm lower than at speed #3. This should mean my boiler is running more efficiently be cause of lower return temps.
  • The_teacher
    The_teacher Member Posts: 8
    Propane usage is downnnnnn crazy! Glad I caught that
  • The_teacher
    The_teacher Member Posts: 8
    I have cut down my propane usage but 40% by slowing down the primary pump.

    Discussion closed