Update 100 year old high mass gravity system with ModCon Boiler

[PC7060]

I have a 1928 house with original expansion tank and piping in a series-parallel configuration (2" primary and 1" and 3/4" radiator feeds). The system was last updated 30-40 years ago when a 145K BTU New Yorker gas boiler replaced an oil fuel boiler and a circulatory pump was added on the return side of the boiler. The boiler is plumbed with a direct In/Out configuration without a by-pass loop causing the boiler to routinely crash during calls for heat.

I mitigated the crashing by adding a Micro Controller (MC) in line with the thermostat low voltage heating call wiring; the MC cycles the pump off and / on based incoming water temperature to ensure the boiler temperature never goes below 140 degrees F.

The heating requirement for the house is 75K BTU based on a heat loss / load analysis of the house performed as part of the to the current renovations. The house has large radiators and heats very well at radiators temperatures of 100-120 degrees on coldest days. All radiators have been updated with Honeywell Brauman TRV.

Requirement: Remove and replace boiler, circulator pump and expansion tank.
ModCon Boiler with outdoor reset and target baseline water temperature of 120F (currently 160F).
Low flow circulator pump configured in a pumping away configuration with expansion tank. Prefer to use a Taco’s ECM high-efficiency 0015e3 or similar.

Optional: Secondary loop for DHW.

Question: looking for recommendation on boilers and equipment configuration.

Concerns: Given the age of the system the new boiler must be able to handle/mitigate "dirty" water.
Thanks in advance.

 

[Fitter30]

So the pipe and radiators are 92 years old. Never had problem with nipples hold the sections of the radiators ,leaking,
valves? How long do you think your piping will last? Pipe rot usually starts at the thread of the nipples and have worked on alot of old piping can't think of any that old. My two concerns is if the system gets flushed dirt and corrosion might move around causing a leak. Second more flow in the system will do the same. The only reason piping has lasted this long is no water leaks, very little fresh water added to system and a low flow rate with the added pump for the gravity system. As for as the new boiler system it isn't so much the brand but does the company put many of these in and are parts locally available. How many hot water system do they install and references. One word not going to mention as bes tos. Hot water would want to know is your have a big tub or large use shower.

 

[Sponsor]

 

[Dana]

I have a 1928 house with original expansion tank and piping in a series-parallel configuration (2" primary and 1" and 3/4" radiator feeds). The system was last updated 30-40 years ago when a 145K BTU New Yorker gas boiler replaced an oil fuel boiler and a circulatory pump was added on the return side of the boiler. The boiler is plumbed with a direct In/Out configuration without a by-pass loop causing the boiler to routinely crash during calls for heat.

I mitigated the crashing by adding a Micro Controller (MC) in line with the thermostat low voltage heating call wiring; the MC cycles the pump off and / on based incoming water temperature to ensure the boiler temperature never goes below 140 degrees F.

The heating requirement for the house is 75K BTU based on a heat loss / load analysis of the house performed as part of the to the current renovations. The house has large radiators and heats very well at radiators temperatures of 100-120 degrees on coldest days. All radiators have been updated with Honeywell Brauman TRV.

Unless it's a fairly large and uninsulated house with leaky single pane windows, a design load of 75K is pretty unlikely at VA's 99% outside design temps.

Manual-J has some fat built in, but a sloppy Manual-J can easily overestimate the real load by a factor of two. If you have a heating history on the place, run a fuel-use based load analysis on (wintertime only) fuel bills. Even if the renovations occured after the winter, with a 90+ year old house, even if the renovations increased the square footage of the conditioned space, the heat load is more likely to have decreased than increased, since the new exterior walls/windows/ roof /foundation would have met current code minimums, with significantly less heat loss per square foot of exterior surface area.

The fact that you have sufficient radiation to heat the place with ~120F peak radiator temps is another clue pointing to a much lower heat load. With that information another way to ballpark the real load is to measure up the "equivalent direct radiation" of all the radiators. At an average water temp of 120F the rads emit only about 50 BTU/hr per EDR' (see the nomograph on p.2 of that document.)

Optional: Secondary loop for DHW.

Question: looking for recommendation on boilers and equipment configuration.

Concerns: Given the age of the system the new boiler must be able to handle/mitigate "dirty" water.
Thanks in advance.

Filters and sediment traps with magnets to pick up any ferrous sludge from the old rads & iron plumbing are a good idea, and readily available.

Fire tube heat exchanger boilers are more forgiving of gunk & crud and can handle higher flow rates when pumped direct than water tube condensing boilers, with much lower pumping head (comparable to the pumping head of small cast iron boilers). Lochinvar's KHB (or WHB) series fire tube boilers would fill the bill. With a max DOE output of 79,000BTU/hr KHB085 is probably overkill for the likely heat load, but with the 10:1 turn down ratio it would still modulate just fine with load yielding very long duration/highly efficient burns when controlled with outdoor reset. A similar and usually cheaper/ easier (often DIY-able) solution is HTP's UFT series. The smallest in series UFT-080 is enough boiler for 95 out of 100 homes in the US, and like the Lochinvar KHB has a 10:1 turn down. It has fewer programming bells & whistles than the KHB (most of which you wouldn't need), and comes pre-plumbed internally with a secondary port & controls to support an indirect water heater.

There are others...

 

[PC7060]

@Dana - Thanks for the detailed and well written response. I apologize for the delay in responding, the boiler update is part of a large renovation and addition and dropped the ball on this thread.

I've attached a system design which includes a Caleffi SEP4 hydraulic separator between the primary and secondary.

The folks at heatinghelp.com (@mattmia2 @hot_rod) provided similar advice regarding the use of a Fire Tube type boiler. I've looked at both the HTI UFT and the Lochnivar Knight; both in the 80K range as you also recommended. I'm currently leaning towards toward the HTI UFT over the Knight, primarily because of cost.

Also received a recommendation to consider the HTI TRX, a water tube boiler with large diameter HX tubing. The TRX looks like a nice unit but couldn't locate a source in Virginia. I'm considering in a Water tube type boiler in addition to the Knight and UFT because of the higher HX reliability and ease of maintenance.

Have you experienced any reliability issues with the UFT? I noticed the Knight has had a couple recent recalls, along with Triangle Tube and Viesmann (must be something in the water).

I appreciate your help!

PC7060

 

[Dana]

HTI??? It reads like you're combining or conflating NTI with HTP, two very different companies. There is generally better support for NTI in Canada and some of the nearby bordering US states. HTP is a US company that also sells many of the same boilers through Westinghouse. Westinghouse labeled HTP boilers have been distributed through the big orange box store. It's the same equipment, different part number, different label, different warranty support, but the Westinghouse tech support line rings at HTPs headquarters in MA. The Westinghouse WBRUNG080W is exactly the same boiler as HTP's UFT-080W

So far the record on the UFT series boilers is pretty good. I personally don't have enough experience to be statistically significant, but a hydronic designer I respect in Maine (who had previously been a Triangle Tube fan) has been specifying dozens of them per year for several years now without negative feedback.

Unless the gpm rates need to be very high for your high mass rads you don't need the hydraulic separator. Almost all single zone UFT systems can be pumped direct with no problem, even former gravity-feed systems, as long as the outdoor reset control is dialed in reasonably. If the "series parallel" configuration is actually monoflow tees it may necessitate higher flows than typical, but also maybe not. The WBRUNG/UFT-080 has a minimum specified flow of 1.3gpm, but only presents 3.1 feet of head at 7.6gpm according to Table 11 on p.29 of the manual.

Also note, there is already a separate internally pre-plumbed port & controls on board the UFT boilers for supporting the indirect coming out the bottom of the boiler, with the heating side port coming out the top. It doesn't have to be teed in externally as shown in your diagram. See the multiple example system plumbing details regarding the indirect starting on page 20 of that manual.

 

[PC7060]

Westinghouse labeled HTP boilers have been distributed through the big orange box store. It's the same equipment, different part number, different label, different warranty support, but the Westinghouse tech support line rings at HTPs headquarters in MA.

HTI! HTP is correct! Thanks for the tip on Westinghouse. I checked big orange, they currently only carry the 199K and 140K size units. Huge units!

Unless the gpm rates need to be very high for your high mass rads you don't need the hydraulic separator. Almost all single zone UFT systems can be pumped direct with no problem, even former gravity-feed systems, as long as the outdoor reset control is dialed in reasonably. If the "series parallel" configuration is actually monoflow tees it may necessitate higher flows than typical, but also maybe not. The WBRUNG/UFT-080 has a minimum specified flow of 1.3gpm, but only presents 3.1 feet of head at 7.6gpm according to Table 11 on p.29 of the manual.

I have standard two pipe configuration with each radiator coming back to the main distribution lines. Planned on using the SEP4 both as separator and to clean up the water. Realize it may be overkill.
So to paraphrase, you are recommending removing the SEP4 and the second loop pump so the primary pump moves all the water through the single zone. This is pretty much how the current system is piped except the old CI does not love the cold return water like the MODCON would. I can add a DIRTMag air separator to clean to up the return water in place of the SEP4. This will certainly simplify the piping.

Is the ability to pump direct a benefit of the low head of the Fire Tube Desing or is it a unique capability of the HTP UFT?

Also note, there is already a separate internally pre-plumbed port & controls on board the UFT boilers for supporting the indirect coming out the bottom of the boiler, with the heating side port coming out the top. It doesn't have to be teed in externally as shown in your diagram. See the multiple example system plumbing details regarding the indirect starting on page 20 of that manual.

Yes, I had dropped the HTP UFT in for a Rinnai I090SN and didn't update the drawing with the connection details. Thanks for pointing me to the installation manual piping examples.

 

[Dana]

HTI! HTP is correct! Thanks for the tip on Westinghouse. I checked big orange, they currently only carry the 199K and 140K size units. Huge units!

Those are probably the combi-units, right?

I have standard two pipe configuration with each radiator coming back to the main distribution lines. Planned on using the SEP4 both as separator and to clean up the water. Realize it may be overkill.

Any air-purging device with a dirt separator (eg Spirotherm) is fine- it doesn't need to be a hydraulic separator. Hydraulic separation is only needed if the system's flow requirements are higher than what the boiler can tolerate, which is usually the case with water-tube heat exchanger type boilers, but only rarely with fire-tube or cast-iron boilers.

So to paraphrase, you are recommending removing the SEP4 and the second loop pump so the primary pump moves all the water through the single zone. This is pretty much how the current system is piped except the old CI does not love the cold return water like the MODCON would. I can add a DIRTMag air separator to clean to up the return water in place of the SEP4. This will certainly simplify the piping.

Yes, it's both simpler and higher efficiency to pump direct. With a hydraulic separator in the mix the supply water going out to the radiation is lower, and the entering water temp at the boiler is going to be higher, resulting in less condensation (=lower raw combustion efficiency).

Is the ability to pump direct a benefit of the low head of the Fire Tube Desing or is it a unique capability of the HTP UFT?

Most fire tube heat exchangers can tolerate 5 gpm+, which is usually more than adequate for residential systems. Most water tube boilers present a large pumping head at those higher rates (chewing through more pumping power), and have a lower maximum pumping rate. (Over-pumping a water tube boiler generates internal erosion of the internal piping, and a shorter lifespan on the heat exchanger.)

With either heat exchanger type there are minimum pumping rates to pay attention to as well- under-pumping results in flash-boil (which is noisy, and reduces the heat exchange efficiency for lower combustion efficiency), and potentially excessively high delta-Ts. Being able to control the boiler's flow rate independently of the radiation flow to guarantee the minimums are always met is another reason to go with a hydraulic separator. Under pumping is unlikely to be a problem on your system since your fat radiation plumbing has low pumping head. If pumped direct (no separator) setting a smart pump to to a constant flow usually works just fine. With the fat-piped distribution loop of your series-parallel system the TRVs will have very little effect on the pressure (unless the pumping rates are pretty extreme), so a constant pressure feedback approach won't really do much.

 

[PC7060]

Under pumping is unlikely to be a problem on your system since your fat radiation plumbing has low pumping head. If pumped direct (no separator) setting a smart pump to to a constant flow usually works just fine. With the fat-piped distribution loop of your series-parallel system the TRVs will have very little effect on the pressure (unless the pumping rates are pretty extreme), so a constant pressure feedback approach won't really do much.

Again, very nice explanation, thank for walking me through the details. Re the constant flow versus constant pressure, the Taco 0015e3 is a constant pressure differential ECM pump (datasheet). Are ECM pump configurable for min (e.g. 2 GPM) and max (e.g. 5 GPM) flow rate?

 

[PC7060]

Updated the design to specify Expansion tank and circulator. Selected Grundfoss ALPHA2 in constant flow mode; lowest setting due the the very low head of the fat pipes in my system. Can set adjust if required; ALPHA2 has a variety of modes.

Added a DISCAL DIRTMAG, probably need to move before the circulator.

Question: Does the DHW require an expansion tank?

 

[PC7060]

Getting ready to order the Indirect Water heater tank.

1. looking at the WM Aqua-Plus 45 and the HTP SSU-45 Indirect Tanks. Both are stainless steel units and look to be very similar in price and performance. Am I missing any key differences?

2. What type of circulator pump is typically used for the indirect water side of the system? Seems like a standard constant rate pump in the 8-12 GPM range is acceptable.

3. Pg. 53 of the HTP UFT I&O Manual discusses the setting for the Indirect Sensor type AquA or SEnS as aquastat or indirect sensor.

How do these two sensor type differ in performance? The HTP SSU manual (pg. 14) describes where to install thermistor but doe not provide a part number.

Thanks!

 

[Fitter30]

Dirt magnet should be piped on suction side of pump to protect pump

 

[Fitter30]

Page 61 table 33 has part numbers for sensors and their resistance

 

[PC7060]

Dirt magnet should be piped on suction side of pump to protect pump

Agree, updated drawing.

 

[PC7060]

Current selecting the DHW circulator to meet the 8-10 GPM flow from the HTP UFT80 through the HTP SSU45 Indirect tank.

I've looking at a 3-Speed Circulator such as the Grundfos UPS15-58FC, however having some difficulty determining what speed selection is optimal since GPM varies with head.

The Pressure drop table on pg. 10 of the the "HTP SuperStor IO&M Manual lp-83" lists a head of 8.3 at 6GPM and 11.3 at 7GPM.

The recommended flow rate listed in HTP SuperStor IO&M Manual Part 2 "B. Performance and Sizing Guidelines" listed head of 6-9 and a recommended GPM of 8 GPM for a 84000 Boiler size.

Based on this the mid level speed of the UPS15-58FC seem like the best option.

Does this seem reasonable? What is the "typical circulator used for this application?

 

[PC7060]

Hi all,

The old boiler is out and have the boiler wall set up and ready for hardware.
I'm planning to connect the Boiler to the existing stainless steel lined chimney locate 4' to right of the boiler (see attached).
I'm having difficulty locating a adapter from 3" PVC to the liner. Any recommendations?
This is a listed historic property which is why I'm using the lined chimney rather then horizontally venting with PVC through front wall of house.

 

[Fitter30]

Flue liners have to be rated for condensing boilers/ furnaces. Google flue liners and condensing boilers. You tube has some videos also.

 

[Dana]

As long the flue isn't being used by other appliance it can (in most cases) be used as a flue-chase for PVC venting. The even if it has a stainless flue liner rated for condensing equipment that flue looks many times oversized to use for a modulating condensing boiler. Even with the forced draft there would be convection loops and excessive condensation inside the flue and too much potential for backdrafting into the house at low fire.

 

[PC7060]

@Dana & @fitter30 - thanks for your information. I've updated design to use side wall vent for flue gas, simpler than running discharge line up 30' of flue.

 

[PC7060]

Wiring is complete and am currently going through the installer configuration settings. Most items I am leaving at defaults but had a couple questions on Boost mode and Anti--Cycle time:

HTP UFT IOM page 51
What is the intended purpose for Boost mode?
----
9:bt
Boost Function:
When Outdoor Temperature Mode is used, Boost Function increases the CH set point temperature by the Boost Degree temperature at time intervals (Boost Interval). Boost continues until the boiler reaches the maximum supply temperature set point based on the outdoor reset curve. The boiler will return to normal operation after the thermostat is satisfied.
Range: 0 - 120 min

-Boost Degree:
Sets the temperature added to the boiler target set point based on the Outdoor
Temperature Mode reset curve. Range: 5 - 15F Default: 10F

-Boost Interval:
Sets the interval time when the boiler will increase the temperature by the Boost Degree. Ex: Initial Boost: 10F. After 20 MIN Interval: Boost will increase CH set point temperature another 10F. After another 20 MIN Interval: Boost will increase CH set point temperature another 10F. This will continue until the boiler reaches the maximum supply temperature set point based on the outdoor reset curve, or until the thermostat is satisfied.
Range: 0 - 120 MIN Default: 20 MIN

----
The default Anti-cycling time is minimal, under what conditions would adjust this time up?
16: Ft CH Anti-cycling time: Default 1 minute

 

[Dana]

Wiring is complete and am currently going through the installer configuration settings. Most items I am leaving at defaults but had a couple questions on Boost mode and Anti--Cycle time:

HTP UFT IOM page 51
What is the intended purpose for Boost mode?

BOOST can be useful for people who prefer to set back the temperature by 5F or more overnight for sleeping comfort. When the BOOST kicks in it shortens the recovery ramp bringing the house back up to temp, without sacrificing efficiency by raising the entire reset curve temperatures to make recovering times reasonable.

In situations where the thermostat approach is "set it and forget it" BOOST doesn't really do anything useful.