Finding BTU rating for hydroair coil

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Old 11-10-20, 09:32 AM
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Finding BTU rating for hydroair coil

My boiler sized properly when all four heat zones in my house run simultaneously. Unfortunately, if 3 zones or less call for heat, the system short cycles.

Two zones are hydroair while the third is a two kickspace heaters with blowers and the fourth is tube-fin baseboard. What's the easiest way to determine the BTU rating for my hydroair unit's coil? Is it printed inside the blower housing? I was hoping they are standard ratings tied to the blower unit model so I can avoid having to dig my way to the system and open it up.

Thanks.
 
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Old 11-10-20, 08:43 PM
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The coils should be labeled but the label may be hard to locate.
It would make sense to be incorporated in the air handler's model number if they were bought as a system.

What is the model number ?
 
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Old 11-11-20, 08:35 AM
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Thanks, PJ. The first airhanlder is the Trane TWE018C140B0 (we were talking about this same unit regarding a 2/3 speed blower motor). The second air handler is a Rheem RBHA-17J00NHDA.

My end goal is to calculate the loads for all of my zone separately and combined to get a better feel for how oversized my boiler is and what are the best approaches for preventing the short cycling that is costing me $$$.
 
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Old 11-11-20, 05:40 PM
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A 4 zone/element system should not short cycle because one is not removing heat.

Would help to see pictures of system along with description of what thread starter defines as "short cycling".
A common definition is run of less than 4 minutes.

Actually, shorter cycles are more efficient. Look at any boiler chart, efficiency falls off after reaching "steady state".An easy way to reduce fuel costs is to lower firing rate with smaller nozzle.
 
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Old 11-11-20, 05:49 PM
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As far as I can tell...... both of those units are generic A/C air handlers for heat pump or electric heat use. Neither shows a heating coil as factory installed. So someone installed them after the fact.
 
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Old 11-12-20, 01:51 AM
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The heating coil capacities aren't an indication of heating requirement, merely what the installer guessed was safe or what was on the shelf at the supply house that day (Do I have an attitude or what?). Please provide some info so we can estimate your home's heating requirement:
1. Size and age of home
2. Nearest city.
3. Any improvements to make the home more thermally efficient (replacement windows, additional insulation, etc.)?

It'd be good to have the boiler make and m/n too. Another thing to consider: Resetting boiler temperature based on outside temperature might lengthen run times.

 
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Old 11-12-20, 08:16 AM
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hi, all.. thanks for the feedback. Here are the details:

House: I purchased it in the end of 2018. It is 1850 sqft, shoreline CT, new haven county. Original structure was about 1100 sqft. Garage was converted to livable space in 1990s and a 500 sqft (2 story) extension was added in 2000. Every part of the house feels well insulated, except the extension. That room is drafty (working on resolving that in another thread), but I often isolate that room so its not constantly driving my boiler to run with calls for heat. On the colder winter days, even when stat is set at 50F, the extension room drop 3F degrees within an hour and call for heat. The house has a mix of old and new windows. All the older windows have a storm pane I keep in place to help insulate. Most of the house is above a 4 ft basement/crawl space. The converted garage sits above slab. All hotwater for the house (heat and DHW) run under that floor so the coldness of the slab isnt felt. The extension room is on slab, which i feel acts like a heat sink pulling all the heat out.

Equipment:
Boiler- Weil Mclain WTGO-4 w/ tankless coil for DHW. about 125k btu i believe. The previous owner did gas conversion in 2018.
Zone 1- two quiet one powered kickspace heaters in series (i think about 8k btu each but i will have to check). this was added in the garage when it was converted to living space
Zone 2- slant/fin baseboards. maybe about 40 ft. covers 2 rooms downstairs.
Zone 3-hydroair (trane unit mentioned above). added solely to heat/cool the downstairs room (leaky room on slab described above) in the extension (a 300sqft room). this zone is over kill and has a super obnoxious wind tunnel effect.
Zone 4- hydroair (the rheem unit above) this primarily heats and cools upstairs. At some point, previous owners added central air and single ducts were added to several downstairs rooms. This supplements the kickspace and slant fans (zones 1 and 2) for heat but, i suppose, was primarily done to get cool air downstairs.

The set up:
Boiler is controlled by a hydrostat 3250 plus. Zones are controlled by Taco SR504-exp relay panel. There are 3 circulators. Zones 1 and 2 have their own dedicated circs near boiler. Zones 3/4 share a circ near the boiler. About 50ft away in a crawl space, two zone valves separate zone 3 and 4. This was how they got heat to the extension hydroair (zone 4). Boiler was relocated to a utlity closet after the basement flooded years ago before me. As a result, the runs to all zones are long and through unconditioned space. The boiler is under glycol antifreeze (i will have to check the % later).

What I am certain of:
- boiler was installed in 2008, gas conversion was 2018
-In summer, 155F is needed for DHW. In Winter, 165F is needed.
-185 has always been sufficient for heating on coldest days
-ODR isnt worth it until i go cold start, ie get rid of tankless coil (i believe?)
-Everything is wired correctly. I know because I removed all the old relays (which were done wrong) and rewired it all myself (lots of thanks to this forum)
- boiler temps (analog, aquastat and FLIR measurements agree) are accurate and pressure is normal.
- expansion tank is good
- There is no return or system bypass so this boiler gets hit with cold crawl space water when circs first start up. Once runs have normalized, return temps are steady and have 20-30F drop from supply temp.

My experience of the cycles:
If all 4 zones kick on together (usually happens to warm the house in the morning after its allowed to cool while we sleep), I clocked the boiler burner going for 15 minutes (until two zones were satisfied). The whole time, it hovered at 178ish, and 180F was my high cut off. This was only one test trial so more need to be done to confirm.

With 3 zones, its about a 5 minute burn followed by about 5-10 minutes off. This repeats until call was satisfied.

If any single zone is running, the burn is about 3 minutes on 3-5 minutes off, except the kickspace heaters which are very low BTU. They will cause a burn for 3 minutes to get to 180F but then rest for maybe 20 minutes or so.


The results:
- horrible gas bills. When I first moved in, during the winter, we were paying near $400/mo when we didnt even live there and heat was set to 50F. Thats when I found zones 3/4 were wired wrong and couldn't fire the boiler to high temp. The installers solution? set the lower limit to 190F and high to 210F. Resolving that helped get the bills down but they still seem a bit high. Also, I do see condensate on the flue for the boiler, indicating the burns are too short to get stack temperature high enough. Im concerned the boiler is slowly killing itself by condensing. While I want to redo all the system at some point, I would rather spend 2k with a fix for the this, especially since the boiler isn't old, then 10k for a whole new system.

I will try to take some pictures this weekend when I get back to the house.

sorry for the long post but here are all the details i can think of right now. thanks all.
 
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Old 11-13-20, 08:58 AM
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Boiler size is frequent question on DIY.com For older homes easy and accurate way to find boiler size is gathering data on existing system.

Pbct2019 raised similar issue on thread in February. His high fuel costs may partially be due to excessive, unneeded high gas firing rate.

Start with Doughess Post #4 and then others on https://www.doityourself.com/forum/b...ing-cycle.html

Rather than getting mired down in system complexity, pbct2019 might start by learning his run time on 0 F design temperature days.

In USA run time of 6 hours a day, 25% of time, is common . Mine is 8 hours/day or 33%.

A current link for timers is:

https://www.ebay.com/sch/i.html?_fro...unter&_sacat=0
 

Last edited by doughess; 11-13-20 at 09:15 AM.
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Old 11-13-20, 04:29 PM
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I know from 70's and 80's Energy Crunch experience heating DHW with a boiler in warm weather is HUGELY expensive. Buy a gas or electric HW heater and then arrange the CW piping to first go through the tankless coil, and for your cast iron boiler to fire only on a call for heat - AND THEN subject to outdoor reset, preferably from a sensor IN the boiler outlet piping as opposed to a strap-on type. The outdoor sensor must be in a shaded location subject to wind movement, of course. The work will be a good investment with a GOOD return. You might want to provide valving to bypass the tankless coil for maintenance, etc.
 
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Old 11-14-20, 04:06 AM
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7F outdoor design for 63F TD. 3,000 to 3,500 SF heated space. Some newer windows with good U factor and some old windows with storms @ U = 0.54. Reasonably well insulated, but some infiltration. Sound about right? If so, maybe 60 to 80 MBH heat loss. Your boiler's IBR rating (that includes an allowance for piping and pickup) is 126 MBH, so it could be twice what's required.
 
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Old 11-16-20, 08:11 AM
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Hi, Ferd. Some of your terms are over my head there. lol. Do you mind explaining the 7F and 63F TD? 7F is the 99% value calculated for my area? Is 63F the target to maintain?

The house is about 1800 sqft of heated space. Windows and insulation sound reasonable.

Thanks.
 
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Old 11-17-20, 12:37 AM
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7F is Manual J 99% value for New Haven, CT. Manual J indoor design is 70F, so the "TD" (temperature difference) between outdoors and indoors is 63F. So the 1,800 or 1,850 SF INCLUDES garage and 500 SF two story addition?

If that's the case, your heat loss is more like 40 MBH and your boiler is about triple what's required:
20MBH (new DE homes @ 52F TD) x 63/52 x 1.5 for existing construction = 36+ MBH

Was the extension slab edge insulated?
 
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Old 11-17-20, 06:52 AM
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Yeah, 1800-1850 sqft includes all of the livable space. The original houe was ~1000 sqft. The attached single car garage was converted into the kitchen (+300sqft) and then an extension was added off the side (+500sqft).

My gut says the slab was not edge insulated on the extension. That room is coldest; on cold days (~30F) around here, the room drops 2 degrees and needs to reheat within an hour. I have my FLIR camera and now, with it cold outside again, I am going to snap some images. The slab is above grade though, not sure if thats good or bad. On the back, you see exposed foundation, on the front and side of the room, you come out onto a deck sitting just above ground level. Ill post some pictures (FLIR and regular) later today.

Side note: I have been sitting here working not far from my boiler and I can here it cycle. With 3 zones and then just 2 zones running (one zone being the low btu kickspace heaters in both scenarios) The boiler burns for 3-4 minutes, rests for 14-15 minutes, and repeats. I have heard it do this consistently for three cycles (cycle one had 3 zones, cycle two had just the two zones running).
 
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Old 11-17-20, 10:06 AM
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Short cycling is an arbitrary concept that creates endless issues.

Typically US heating systems run 25% of time ( 8 hours/day) at design temperatures of say 0F. At 32 F outside temperatures runtime would be 4 hours/day= 240 minutes = 20 minutes hour

Based on quotes from this thread below PBCT2019 runtime data (no outside temperature) is consistent with boiler size. Since at lower run time efficiency is highest, fuel cost lowest why change things?

Quote #1 Your boiler's IBR rating ... is 126 MBH, so it could be twice what's required.

Quote #! The boiler burns for 3-4 minutes, rests for 14-15 minutes, and repeats. I have heard it do this consistently for three cycles (cycle one had 3 zones, cycle two had just the two zones running).

Final note: Do not recall seeing any DIY posts on downside of short run times.

 
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Old 11-17-20, 11:15 AM
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Thanks, DougHess. Its currently 45F and I have been working at the kitchen table where I can hear the boiler cycle; I can certainly say I am averaging more than 10min per hr but probably not 20 min per hr. During earlier morning heat up of the house, I was averaging around 15 minutes burn time per hour (15min off, 4 min on). Once that call was satisfied I probably burn 5-6 minutes per hour (maybe two cycles). I will need a timer like you suggested to be certain.

Regarding ideal burn duration:
I always operated under the impression that boilers are more efficient the longer the burn goes; ie, one 10 min burn is more efficient than two 5 min burn with a break in-between. More so, I am concerned that the short burns and more frequent cycling will result in the boiler not reaching sufficient temperatures (and sustaining them) to burn away condensate, leading to an early death of the boiler. Maybe I have been wrong?

Manual J Calc:
I did just use loadcalc.net to do a bulk manual J for my house. Its pretty rough estimates but my calculation came out to 65,000 btu, pretty close to Ferd's. Dimensions were rough and insulation rating was a guess ( I chose R19)
 
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Old 11-17-20, 11:43 AM
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"Typically US heating systems run 25% of time ( 8 hours/day) at design temperatures of say 0F"

D: Please explain. It looks like you're saying typical systems are oversized by a multiple of four. Is that your experience?

P: My first estimate was based on 3,200+ SF, but I revised it down to 36MBH when I realized the home was only 1,800+.
 
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Old 11-17-20, 04:57 PM
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The 20% or 25% is commonly mentioned number. Another is 85% of USA heating system are twice size needed.

Many boilers were sized and installed in lower cost fuel times year ago.

Many of those homes have since been insulated, new windows installed lowering heat load resulting in over sized boiler.

Doughess experience: Fifty years ago used 1800 gallon of oil per year. Last season used 600 gallon.
Burner is now retention head, 40% smaller nozzle, out-door rest, new windows, lots of insulation, etc.

Here in New York city area 4,300 DD is average. Could not find annual DD for SF but issues are different.
 

Last edited by doughess; 11-17-20 at 05:15 PM.
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Old 11-17-20, 05:57 PM
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Short cycling is an arbitrary concept that creates endless issues.

Typically US heating systems run 25% of time ( 8 hours/day) at design temperatures of say 0F. At 32 F outside temperatures runtime would be 4 hours/day= 240 minutes = 20 minutes hour.

PBCT2019 runtime data (no outside temperature) in quote below is consistent with his boiler size. Since a lower run time efficiency is highest, fuel cost lowest why change things?

Quote #1 Your boiler's IBR rating ... is 126 MBH, so it could be twice what's required.

Quote #! The boiler burns for 3-4 minutes, rests for 14-15 minutes, and repeats. I have heard it do this consistently for three cycles (cycle one had 3 zones, cycle two had just the two zones running).

Final note: Do not recall seeing any DIY posts on downside of short run times.

 
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Old 11-18-20, 11:33 AM
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@Doughess -- Interesting. In my limited, but fairly thorough research, I have always read that boiler efficiency is improved with run time and that short cycling is bad for equipment and efficiency. I certainly could be wrong here but I would be interested to hear others takes on this.
 
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Old 11-18-20, 07:29 PM
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pbct2019: There is no “Ideal run time”. Boilers run because heat was removed and aquastat started it. Outdoor temperature varies, changing run times over the season. in San Francisco where there is little temperature range over the year there is small run time variation.

There is no connection between condensation which occurs at 133F and cycle time. Because most boiler minimum temperate is set above 133F, condensation is not an issue, no matter how short the cycle. So there is nothing to burn off.

The Short cycling “thing” is an arbitrary concept that creates endless issues for novice DIYers

If my boiler ever cycles less than 2 minutes will have to think about it. Till then, will deal with more pressing issues in life.

.

 

Last edited by doughess; 11-18-20 at 07:58 PM.
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Old 11-19-20, 03:10 AM
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It's interesting that posts must have a minimum number of letters. I tried to just say "Right".
 
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Old 11-19-20, 10:12 AM
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Doug, your opinion is quite clear (as is normally the case). As I stated, I am looking to hear others because there is a wealth of information out there that contradicts what you are claiming and no references are given for what you claim are typical run times and sizing.

As well, I am more so referring to condensation in the flue as the burn may not be long enough to reach a sufficient stack temperature. Maybe this is just another "myth" used to trick "novices". But then again, condensate coming down my flue says otherwise.
 
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Old 11-19-20, 02:51 PM
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Flue temp is definitely an issue, and I had to drop a SS liner into the deteriorated clay liner of my 1933 chimney due to condensation created by low boiler temperatures resulting from outdoor reset and cold start when we sold the home. There was nowhere to horizontally discharge because of the close property line along the side, but It was still worth it.

FYI: I rarely see 4X oversized heating equipment and very few locations in CONUS have a 0F outdoor design temperature, and those that do rarely stay 0F 24/7 because of that big, bright orb in the sky.

D: It would be good to see the documentation of your 8/24 claim, please post a link; hoping to learn something.
 

Last edited by ferd42; 11-19-20 at 03:20 PM.
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Old 11-20-20, 10:41 PM
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Lesson #1: Design temp is not 24/7. Degree day, mean temperature is common reference:

https://www.engineeringtoolbox.com/u...ity-d_296.html

I live in 0 F New York city area. Last winter it went to -6 F.

Wilmington, DE which is 0 F which may be enlightening news to DIY posters who live nearby.
 
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Old 11-22-20, 12:04 AM
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The operative Standard is ACCA Manual J, not Engineering Tool Box. Wilmington, DE is therefore 14F. Haven't used 0F in decades.


 
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Old 11-23-20, 01:30 PM
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Charts are tools, some good, others not. The leading professional global source of heating/cooling data is “ASHRAE” the American Society of Heating, Refrigerating and Air-Conditioning Engineers https://www.ashrae.org/

ASHRE New York Laguardia Airport data: ( 10 miles from DH home)
https://www.doityourself.com/forum/b...ml#post2874513

A good over view of heating is: US Dept Energy link: https://www.energy.gov/energysaver/h...es-and-boilers

Below is data from DH system supporting 24/7:
Collected data from outdoor thermometer, degree days, boiler and oil purchases then try to optimize setup.

House 1957 wood frame split level, 1600 sq ft , 2" builders insulation, original oil fired boiler. Reduced oil usage from 1970 1800 gallons @ $0.15 to 2020 600 gallons @ $2.00.

Oil crisis in 1970's was great motivator. Cost of improvements less than $5,000. Annual cost savings $2,400 = 2 year pay back .

Occupied room temperature 72 F. Run on time 0 F day = 8 hours/24 hour day, 33% of time. Boiler fired at 66% of rated BTU, stack temp 350 F, 86% efficiency.
 

Last edited by doughess; 11-23-20 at 02:00 PM.
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Old 11-23-20, 02:42 PM
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Yes, the ultimate Authority is "ASHRAE", ASHRAE 99% Values are what Hank et al use to develop ACCA Manual J design temperatures. I see Wilmington's design is now "17.7"F and Laguardia's design is now "15.9"F in the ASHRAE 2017 "Fundamentals" Handbook. I assume ACCA will catch up that in their next Manual J update.

Please let me know if you'd like me to post the applicable ASHRAE pages.

Moderator(s): Is this getting away from OP's question?
 
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Old 11-23-20, 06:08 PM
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Thread Starter pbct2019 opening words are about boiler size:

"My boiler sized properly when all four heat zones in my house run simultaneously. Unfortunately, if 3 zones or less call for heat, the system short cycles."

Short cycling is a hot topic for some that leads to many goose chases.

That is why Doughess Post #4 suggested learning adequacy of his boiler: “Rather than getting mired down in system complexity, pbct2019 might start by learning his run time on 0 F design temperature days. “ From that data he can learn run time at any outside temperature day and appropriate cycle time.

Unfortunately, as often happens on DIY.com things went of on tangents like “design temperature”
 

Last edited by doughess; 11-23-20 at 08:00 PM.
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