Another tankless water heater replacing boiler thread

[OurTown]

85 return is too much with the units set at 120F. I bumped it back down to 80 and lowered the on temp to 60. Also I lowered the unit output temp to 110 so that they run longer.

 

[Roz]

How old is your system?

Have you tested your glycol to see the rating?

You might benefit from new glycol and perhaps a stronger dilution. We test our glycol and change it if necessary every few years.

Our mixture is good to zero deg perhaps slightly below zero as the extra cost for the glycol is nothing in comparison to having to close or having ice issues. Glycol costs have tripled since 2020 pandemic but are now starting to come down slightly.

 

[2Biz]

85 return is too much with the units set at 120F. I bumped it back down to 80 and lowered the on temp to 60. Also I lowered the unit output temp to 110 so that they run longer.

I set mine up at 32° or there abouts...At 32° after it normalizes and heater set to 105°, my cycle times are 15 minutes on/15 minutes off with a 15° differential from 55° to 70°. Glycol going to the bays is 90°. At 15° OAT, the system automatically adjusts and on time is about 18 minutes/off time is 12 minutes. At zero OAT, cycle time is about 22 minutes on/8 minutes off or close to that...At 15° bgelow zero it still has capacity and cycles off. Just can't remember how long.

Maybe you could also lower your heater temp so it stays on longer...I think you need at least 15-20 minutes on cycle (at these temps) to soak the slab to keep it from freezing. And then again, maybe your tubing is buried deeper than mine like I mentioned dearlier. There are a ton of varaibles that youll just have to figure out what works best for your installation. The big variable betwee nyour and mine is the zone pump...You are running a lot bigger pump, and also you have two heaters giving you double the volumn....Its heating a smaller thickness too quickly causing it to cycle off too soon....

 

[OurTown]

I set mine up at 32° or there abouts...At 32° after it normalizes and heater set to 105°, my cycle times are 15 minutes on/15 minutes off with a 15° differential from 55° to 70°. Glycol going to the bays is 90°. At 15° OAT, the system automatically adjusts and on time is about 18 minutes/off time is 12 minutes. At zero OAT, cycle time is about 22 minutes on/8 minutes off or close to that...At 15° bgelow zero it still has capacity and cycles off. Just can't remember how long.

Maybe you could also lower your heater temp so it stays on longer...I think you need at least 15-20 minutes on cycle (at these temps) to soak the slab to keep it from freezing. And then again, maybe your tubing is buried deeper than mine like I mentioned dearlier. There are a ton of varaibles that youll just have to figure out what works best for your installation. The big variable betwee nyour and mine is the zone pump...You are running a lot bigger pump, and also you have two heaters giving you double the volumn....Its heating a smaller thickness too quickly causing it to cycle off too soon....

I adjusted the temps so that the next cycle took one hour and 40 minutes ON and 15 minutes off. Scrubbing about 22 degrees off at the time I looked at the gauges. After that, I didn't look at what it normalized to. It seemed to work much better so I opened the SS bays. The sun came out and warmed up outside about 10 degrees. Then about 5 o'clock I noticed the slabs freezing so I shut the bays back down. I'm pretty sure we wouldn't have this issue on days like this with our old 627K boiler if I turned up the slab stat enough. One thing I noticed is that the heaters' GPM is only about 11 total no matter what the rise is, so I will clean the inlet screens again. (probably for the 10th time)

 

[OurTown]

How old is your system?

Have you tested your glycol to see the rating?

You might benefit from new glycol and perhaps a stronger dilution. We test our glycol and change it if necessary every few years.

Our mixture is good to zero deg perhaps slightly below zero as the extra cost for the glycol is nothing in comparison to having to close or having ice issues. Glycol costs have tripled since 2020 pandemic but are now starting to come down slightly.

The heating units and pumps are new and half of the in-slab tubing is new. The ethylene glycol (not propylene glycol) is old and tests to -45F freeze temp and about 9.5 pH.

 

[2Biz]

I adjusted the temps so that the next cycle took one hour and 40 minutes ON and 15 minutes off. Scrubbing about 22 degrees off at the time I looked at the gauges. After that, I didn't look at what it normalized to. It seemed to work much better so I opened the SS bays. The sun came out and warmed up outside about 10 degrees. Then about 5 o'clock I noticed the slabs freezing so I shut the bays back down. I'm pretty sure we wouldn't have this issue on days like this with our old 627K boiler if I turned up the slab stat enough. One thing I noticed is that the heaters' GPM is only about 11 total no matter what the rise is, so I will clean the inlet screens again. (probably for the 10th time)

Something is not making sense...At the beginning of the cycle, mine scrubs off 35°, from 90° out to 55° return...I get right at 5.9-6.0gpm with one heater. Its been that way for 10 years without touching a thing or cleaning the tiny filter. I'm out of suggestions for you except keep raising the on/off temp to where the slabs don't freeze. Basically doing the same thing as what you did with the boiler.

 

[OurTown]

Something is not making sense...At the beginning of the cycle, mine scrubs off 35°, from 90° out to 55° return...I get right at 5.9-6.0gpm with one heater. Its been that way for 10 years without touching a thing or cleaning the tiny filter. I'm out of suggestions for you except keep raising the on/off temp to where the slabs don't freeze. Basically doing the same thing as what you did with the boiler.

I bumped the heater output to 120 and the stat to 65/85. It's about 10 or so degrees warmer than yesterday so I'm sure that will help. It seemed to work better weeks ago with that cold snap so something has changed. Just opened my gas bill and it is $750. That was Dec 7-Jan 8. Can't wait for the next one.

 

[2Biz]

Did you ever run a 5 micron filter inline to get all the crud out? My current duke bill is half yours, but understandable! I'll take it. I couldn't afford to run the old boiler that was in there. $150.89 is just additional rider fee's! Last month total was $268.34...

 

[OurTown]

Did you ever run a 5 micron filter inline to get all the crud out? My current duke bill is half yours, but understandable! I'll take it. I couldn't afford to run the old boiler that was in there. $150.89 is just additional rider fee's! Last month total was $268.34...

View attachment 12581

I ran the glycol through a 5 micron whole house filter when filling. Then I circulated it a little longer but I think you ran yours for a day or two IIRC. I needed to get it up and running right away so I didn't run it that long but probably should have.

 

[2Biz]

You are right. I ran it through the 5 micron filter for at least a day using a sump pump in a 15 gallon soap drum.

 

[2Biz]

I ran the glycol through a 5 micron whole house filter when filling. Then I circulated it a little longer but I think you ran yours for a day or two IIRC. I needed to get it up and running right away so I didn't run it that long but probably should have.

This winter is putting your new floor heat through its paces! Reminds me of 2014 just after I got mine installed only it was actually worse then... Just checking to see if you have it dialed in yet? We are in for another winter advisory for tomorrow and Wednesday here in Southern Ohio...Models show we could be in the 4-8" range! I hope they are wrong. I sure will be glad when it warms up. Next weekend looks promising!

 

[OurTown]

This winter is putting your new floor heat through its paces! Reminds me of 2014 just after I got mine installed only it was actually worse then... Just checking to see if you have it dialed in yet? We are in for another winter advisory for tomorrow and Wednesday here in Southern Ohio...Models show we could be in the 4-8" range! I hope they are wrong. I sure will be glad when it warms up. Next weekend looks promising!

It works okay if I crank it way up on the aquastat when it gets cold. It would be nice if I could figure out how to get some type of thermostat to work that measures the slab surface temp.

 

[2Biz]

I'm just wondering if my lines are closer to the surface of the concrete than yours are and making a difference? Mine has been set the same way for over 10 years and don't have to touch a thing? The return aquastat should be all thats needed, but I understand the reasoning about having a slab stat. But a slab stat only tells you what that square foot of concrete is doing, not the whole slab....Do you have your zones throttled based on distance from the ER? If you look at my manifold in the ER, the furthest valve is to my truck bay, its wide open. The nearest valve is the trough loop, it is closed the most....Are you getting even heating acoss all slabs/zones?

 

[OurTown]

I'm just wondering if my lines are closer to the surface of the concrete than yours are and making a difference? Mine has been set the same way for over 10 years and don't have to touch a thing? The return aquastat should be all thats needed, but I understand the reasoning about having a slab stat. But a slab stat only tells you what that square foot of concrete is doing, not the whole slab....Do you have your zones throttled based on distance from the ER? If you look at my manifold in the ER, the furthest valve is to my truck bay, its wide open. The nearest valve is the trough loop, it is closed the most....Are you getting even heating acoss all slabs/zones?

My old tubing is under 8" of concrete but the new tubing is about 4" under the surface and has insulation under the 6" slab. All valves on the tubing manifolds are full open. Based on the original Super Wash tubing layout drawing that I have they may all be similar length runs. When ice does form it's in many areas but it's much more of an issue on the old slabs. I could probably throttle back the new runs a little bit. I'll see if I can get good return temp readings on each tubing return with my infrared thermometer first before messing with the valves.

 

[2Biz]

My old tubing is under 8" of concrete but the new tubing is about 4" under the surface and has insulation under the 6" slab. All valves on the tubing manifolds are full open. Based on the original Super Wash tubing layout drawing that I have they may all be similar length runs. When ice does form it's in many areas but it's much more of an issue on the old slabs. I could probably throttle back the new runs a little bit. I'll see if I can get good return temp readings on each tubing return with my infrared thermometer first before messing with the valves.

Its been too long ago, but I remember checking each bay slab with an infrared gun and making manifold adjustments based on surface temps. But I might have also checked the return temp of each bay/zone with the infrared gun to tweak...Sounds like you are on the right track, just need to throw more heat to the zones that need it! Once you balance the whole system asfar as surface temps, thats the best you can do as far as efficiency....Then its a matter of setting your aquastat differential and output temp of the wall heaters.....

 

[OurTown]

I just opened my latest gas bill and it was $1,266.

 

[2Biz]

Ouch! Mine was $362....Even with $160 in additional fee's because its classified as commercial! Don't you have an automatic too?

 

[GoBuckeyes]

I just opened my latest gas bill and it was $1,266.

Are you happy with that compared to the past?

How many MCF's was that for and what all is using gas? Refresh us on the wash layout....number of bays, auto etc. What are you paying per MCF for gas?

We're getting some of the largest bills we've had in quite a while. I'm paying $3.95 per MCF.

For comparison:

We have a 4/1 that has two equipment rooms with forced air gas heaters, infrared back up heaters, an 80 gallon hot water tank for the auto, a raypack hot water heater for the self serve, and two raypack floorheat boilers. Last month it used 175 MCF (29 days) and the bill was $1,110.

We have a 5/2 with one equipment room, forced air gas heater, infrared back up, 80 gallon trough heat, big raypack hot water boiler, and raypack floorheat boiler. Last month it used 218 MCF (32 days) and the bill was $1,382.

January was also a very busy month.

 

[OurTown]

Ouch! Mine was $362....Even with $160 in additional fee's because its classified as commercial! Don't you have an automatic too?

Yes. Heating the glass building but nothing else on the new auto.

 

[OurTown]

Are you happy with that compared to the past?

How many MCF's was that for and what all is using gas? Refresh us on the wash layout....number of bays, auto etc. What are you paying per MCF for gas?

We're getting some of the largest bills we've had in quite a while. I'm paying $3.95 per MCF.

For comparison:

We have a 4/1 that has two equipment rooms with forced air gas heaters, infrared back up heaters, an 80 gallon hot water tank for the auto, a raypack hot water heater for the self serve, and two raypack floorheat boilers. Last month it used 175 MCF (29 days) and the bill was $1,110.

We have a 5/2 with one equipment room, forced air gas heater, infrared back up, 80 gallon trough heat, big raypack hot water boiler, and raypack floorheat boiler. Last month it used 218 MCF (32 days) and the bill was $1,382.

January was also a very busy month.

It is the highest bill I have ever seen and we used 1,372 CCF. With the previous set up we had a $1,100 bill once but most of the time it was more like $500 or so but I'm not sure what the usage was. We used to have a typical Super Wash with 3 SS bays and 1 autos with a total of 1,050,000 BTU equipment. Now we have 3 SS bays and one much larger auto, and we have 827,000 BTU input, but we are now heating a glass building. Three 95% efficient 199K tankless water heaters (two for floor heat, one for DHW), two 100K infrared tube heaters in the 20' X 65' glass building, and a 30K infrared heater in the pump room.