Taco 1" zone valve reduces to 1/2" internally

wmarler · July 2023

I have a 1" pipe line to a sidearm hot water heater and I bought a 1" Taco zone valve (Z100T2-3) to control flow to it. The valve BODY is 1", but internally the diameter reduces to 1/2". The same is true for a 3/4" Taco zone valve (Z075T2-3). I don't want this; I want the full flow rate 1" and 3/4" pipe provides.

Did I buy the wrong valves? Are Honeywell valves the same?

Thanks,

mattmia2 · July 2023

look at the Cv before you buy. honewell has higher Cv valves, I think caleffei does too. the taco heat motor valves that sort of look like a metronome also have a higher Cv

mattmia2 · July 2023

it was discussed here:
https://forum.heatinghelp.com/discussion/192825/taco-zone-sentry-question

STEAM DOCTOR · July 2023

Don't think so. You need to check the CV rating for the various zone valves.

Big Ed_4 · July 2023

I agree , why use a zone valve ? The full port model never made sense to me either ... Better to use another circulator if you want full btu.....

EdTheHeaterMan · July 2023

Most Hydronic zone valves are reduced internally. This is not a problem in most cases. You need to remember some basic laws of physics as they apply to water flow. For example, in order to keep the flow of water from making too much noise you will want to keep the Gallon Per Minute GPM slow enough so that you don't hear the water moving through the pipe. For a 1" pipe that would be about 8 gallons per minute. For a 3/4" pipe that might be about 4 GPM and for 1/2" pipe that might be 1.5 GPM. If you allow the water to flow faster, 5 GPM thru a 1/2" pipe for example, you will hear the water flowing thru the pipe quite well. Try opening the bathtub faucet on the second floor and listen to the water flow thru the pipe in the basement. That water flow will be noisy.

The reason we don't want to have the water flow that fast in a heating system is because we don't want to hear that type of noise whenever the thermostat calls for heat. So we keep the water moving slowly in that plumbing system. The potable water system noise is acceptable because we control that noise with a manual valve that we open and we expect to hear the water flowing.
Now that we understand the reason for the GPM in a 1” pipe should be limited to 8 GPM, we also know that 8 GPM at a 20°∆T we can get 80,000 BTU of heat to flow from the boiler to the heat emitter or indirect water heater with 1” copper pipe.

Now we can look at the valve in this 1” pipe and determine that if the valve has a ½” opening in the valve body that there will be a restriction of flow for less than ½” of the travel through that portion of pipe. Now consider that for that very small distance the water flow thru that ½” section of valve the water flow will be 8 GPM at a very fast speed then almost instantly the flow slows down to speed of 8 GPM in 1” pipe. The amount of time and distance that the water flows quickly thru the zone valve is so small that you don't get a large reduction of flow and toy dont get a large amount of noise either.

There may be a small decrease in the flow from 8 GPM to maybe 7.7 or 7.8 GPM but that is usually not enough to make you purchase a full port zone valve at a higher price. That is what the Cv rating is all about. Full Port Motorized Ball Valves are available but they may not be necessary.

EdTheHeaterMan · July 2023

There is a motorized ball valve from US Solid that offers a 1" valve for sale at a reasonable price. I'm not sure how many operating cycles there are in this product. I used them on an irrigation system. They have far fewer cycles per day (1 or 2 per day) than you might find on a Hydronic heating zone (2 to 5 cycles per hour) so I can't say that they are the better choice over a Zone Valve that is specifically designed for Hydronic system use. https://ussolid.com/u-s-solid-motorized-ball-valve-1-stainless-steel-electrical-ball-valve-with-full-port-9-24-v-ac-dc-2-wire-auto-return.html

I have found that zone valves of different diameter pipe connections have the identical internal dimensions for the 1/2", 3/4", 1", and 1-1/4" valves from Honeywell, Taco, Erie and others. This always made me wonder about that restriction however later on I was told about the restriction making the water flow faster thru the restriction for a very, very small portion of the travel from point A to point B and how there is very little actual reduction in flow.

But having that 1/2" orifice on a 1-1/4" pipe has to be more restriction than say a 1/2" orifice on a 3/4" pipe. This is where you need to know what GPM you actually need, what your pump will deliver thru that piping system and what the Cv rating of the valve restriction will actually offer you in the way of actual GPM allowed thru the valve. There is mathematics that will tell you the answer. @Hotrod is well versed on this. He will be able to direct you to a publication that gives you the answers you need.

wmarler · July 2023

TREMENDOUSLY useful @EdTheHeaterMan ty!

This makes me want to configure a variable-speed system, where different pump motor speeds are commanded by the zone controller based on which zones are calling for heat. If one of zones 1 or 2 are open, which have 3/4" pipe then 4gpm; if only the hot water heater is calling for heat then 8gpm. If 1&3 or 2&3 are calling for heat then 12gpm ... And if all zones are calling for heat then open it all the way up to 16gpm.

I'm guessing that's pretty overkill for the modest house I live in :-p. I'll likely use the valves I've got, understanding that although flow is indeed restricted through the 1/2" port, it doesn't restrict flow enough to matter, given the low flow rates in question (8gpm max). I understand that I'm able to get that full 80,000 BTU of heat xfer from boiler to hwh -- which really is my concern -- regardless of whether I use a full port ball valve or a restricted port ball valve.

Thanks again

mattmia2 · July 2023

wmarler said:
TREMENDOUSLY useful @EdTheHeaterMan ty!

This makes me want to configure a variable-speed system, where different pump motor speeds are commanded by the zone controller based on which zones are calling for heat. If one of zones 1 or 2 are open, which have 3/4" pipe then 4gpm; if only the hot water heater is calling for heat then 8gpm. If 1&3 or 2&3 are calling for heat then 12gpm ... And if all zones are calling for heat then open it all the way up to 16gpm.

I'm guessing that's pretty overkill for the modest house I live in :-p. I'll likely use the valves I've got, understanding that although flow is indeed restricted through the 1/2" port, it doesn't restrict flow enough to matter, given the low flow rates in question (8gpm max). I understand that I'm able to get that full 80,000 BTU of heat xfer from boiler to hwh -- which really is my concern -- regardless of whether I use a full port ball valve or a restricted port ball valve.

Thanks again

Delta p circulators do that automatically if you set up balancing valves to balance the zones. Caleffi and Honeywell definitely have valves with a Cv in the 10-12 range. You can also use valves with a Cv of around 3 for the smaller zones.

wmarler · July 2023

mattmia2 said:
Delta p circulators do that automatically if you set up balancing valves to balance the zones.

=-O

Well, I'm certainly glad I reached out for help. That seems like a great suggestion, I'd never have discovered this on my own. Thanks!

hot_rod · July 2023

Assuming the valve manufacturer actually flow tested a valve, the Cv number should = the number of gpm the valve will flow with a 1 psi pressure drop across it.

if the valve were on a domestic water system with 60 psi incoming pressure, when you are flowing 8 gpm thru a 8 Cv valve the pressure would be 59 psi on the outlet of the valve.

In hydronics the speed or velocity that water flows should be limited to 4 or 5 fps feet per second, to keep the system quiet and still get turbulent flow for good heat transfer.

So 3/4 type L copper flowing at the speed of 4fps would equate to about 6 gpm. So really no need to have a valve with a higher Cv than 6-7 for zoning 3/4 copper circuits.

In some cases you can run up to 8 fps in 3/4 copper on cold domestic piping, so about 12 gpm. A high Cv valve would be best if in fact you were to run those high flow rates thru an on off zone valve.

A valve used on those whole house automatic leak detection systems would want to be a high Cv valve. A ball type zone valve can shut off much higher pressures say 150 psi, another reason to use it in a domestic water piping system.

With the most common spring return type zone valves Honeywell, Caleffi, Erie, WR, and others, the spring tension is what closes off the flow, so typically up to 75 psi shut off in spring return, low Cv valves, a 1- 2 Cv for example.

A very common 7- 8 Cv spring return zone valve would shut off 15- 20 psi. Which is plenty for residential zoning applications both Cv and shut off rating.

mattmia2 · July 2023

I think they want to use it for an indirect.

HomerJSmith · July 2023

This may come as a surprise to many, there was a time when cars had a device called a carburetor. The purpose of the carburetor was to put a mist of gasoline in to the cylinder of car motors. The thought was that if you ignite that gas mist in the cylinder you might turn that into power to drive the motion of the car. Many thought it was surely a pipe dream. The theory of the carburetor was based upon the venturi effect. However, physics has shown that the effect is real natural phenomena. Perhaps, that might explain wmarler's observation.

Simple!

hot_rod · July 2023

Yes, same principle at play in hydronics, a speed increase as flow goes through a restriction

put your finger over the end of a garden hose to see the concept at work. Restrict the opening and the water sprays further. Velocity has increased.

However too much restriction can lead to cavitation.

When you kink a garden hose almost closed, that crackling sound you hear is cavitation

hot_rod · July 2023

Depends on the indirect as far as piping and zone valve selection.

Here is an example of two different 40 gallon tanks and the coil flow capacity.

Really no advantage to using more than a 3/4 zone valve and 3/4 piping on the one, as the manufacturers suggests. 5 gpm @ 10' head.

The other, with much larger coil can handle 14 gpm @5.7' head. 1' or 1-1/4" piping depending on the piping length and fitting count for that tank. If you want full performance and have the boiler to drive it.

If you have 80K of boiler, no need to pipe larger than 1" to the tank, even with the large coil indirect.

mattmia2 · July 2023

We need to know the boiler size and size of the hx in the indirect to know if a bogger zone valve would make a difference.

wmarler · July 2023

Thanks for taking this question and running with it! I earned a degree in mechanical engineering way back in 2004; I'm no longer in that profession, but the engineering mindset persists... which is to say, I like to do the math. Unfortunately I do not fully understand in hydronics how it all fits together.

It seems some background on my project would be useful here. My house was built in 1959, and in 2017 we had the boiler replaced. We contracted the work, and I wasn't very involved; at the time though we shifted from having a standalone gas-fired hot water heater to an indirect model (HF-50). Our new boiler is a Lars Minitherm VJS075NDIIU2 (Manual here), which is 75,000BTU. The first winter it was installed we had to call the installers back b/c the boiler couldn't keep the house up to temp; they came back and changed something
-- I can't say for certain, but I think they switched the internal temperature maximum from 180F to 210F -- and we were alright. I didn't pay a lot of attention at the time.

2-3 years ago I started noticing that the baseboard floor radiators would get hot in the middle of summer. I believe I have one of several conditions occurring: 1) a leaking zone valve to the rest of the house (not a problem with the actuator; the actuator did in fact fail, and was replaced, in 2021), and 2) an improper bypass connecting the supply-side to the return-side when the zone valves are closed; there is a partially-closed ball valve in a leg connecting the boiler output to its supply.

Last but not least, we are planning an addition to the house, adding another floor (going from 3k sqft -> 4k sqft).

SO "yadda yadda yadda" I have since learned about hydronics, and how my house stays warm. And coming from that engineering background, and generally being interested in understanding how things work and wanting to learn new things, I thought I'd tackle fixing things. Here are my goals:

Fix the problem of heat coming through the baseboard units when the HWH calls for heat
Split the 2-zone configuration I have now [DHW + house] into 3-zones [DHW + upstairs + downstairs] (I should mention: I can clearly see where the piping goes under the slab and comes back out, as well as where the piping goes into the ceiling and comes back out, as well as where the two supply & return legs come back, and where there is a single valve before they split on the supply line), with the ability to add a 4th zone easily in the future.
Install a pair of unions where the supply & returns connect to the boiler, so the boiler can be swapped in the future more easily
Install a proper connection between the supply and return legs with a differential-pressure bypass valve rather than a ball valve
Install easy-to-use-and-operate purge ball valves (my purging system now leaves something to be desired; there's essentially a single ball valve for the entire system. There are some gate valves that look to be original to the install, which I'm afraid to use, expecting that they won't seal shut once I open them)
Replace two of my baseboard floor radiators with staple-up, between-joist radiant heat in a section where I have ceiling access from the basement.
Add some temperature probes so I can easily know my ΔT across the boiler & radiant heat loop
Make intelligent engineering-based decisions around the components.
Make it a thing of beauty to behold and be proud of, that will last for 30 years and be easily & well-understood by a future service tech on a call

I drew a schematic, available here and also attached to this post.

My radiant heating loop is approximately 200' long. My HWH is an HF-50, and has 1" inlet & outlets; I was going to use 1" type K (less than 10' worth) and I anticipate 4 elbows in the indirect loop. My downstairs baseboard loop is 3/4" type K, it's approximately 100' long with approximately 24 elbows. My upstairs baseboard loop is 50' of 3/4" type L and 30ft of 3/4" oxygen-barrier PEX-A, with approximately 13 elbows (not counting the 3-way diversion valve or the branch going to the water-water heat exchanger). My boiler has 1-1/4" inlets & outlets.

A also sketched pictures to better understand the change in the upstairs zone; see current upstairs heating run and intended upstairs heating run. The ~30' of PEX-A is how I'm removing 2 baseboard radiators from the loop.

I'm not going to say "cost is no object," but I am less sensitive to cost than I think a typical customer receiving a quote from a contractor would be. I like to have nice things; I like my things to work well.

So that's the backstory

.

I'm somewhat amazed to see how my question of "1-inch pipe reduces to 1/2-inch in a zone valve, ****?" has blossomed and grown. The answers have all been extremely interesting and informative, and I thank all of you for your help. At the end of the day, I'm satisfied by the answer of "Taco and Honeywell (and others) use the same orifice inside of their 1/2", 3/4", and 1" zone valves because at the intended flow-rates of residential hydronic systems, the cross-area reduction through the valve has no effect on the rate of flow through the valve, and the negative acoustical impact is minimal. While the size reduction does cause noise, the length of the reduction is small enough that the noise is at worst barely noticeable, and likely entirely mitigated by virtue of being in a mechanical room. By using the same size internals, these companies can bring their costs down in a competitive market." These aren't valves like lawn sprinkler valves where maximizing flow through the valve is the concern and nobody spends a moment's thought on acoustics.

Now that I've shared the backstory and schematics though, if anyone has any feedback for me, please feel free to share. In hindsight I'm thinking I should have reached out sooner! (and if this topic has diverged far enough to be more appropriately placed in a different forum, I am not offended if a moderator were to move it : ).

EdTheHeaterMan · July 2023

That is a good start. Separate zones for the upstairs and the downstairs will surly solve the trouble you have with the inability to heat on very cold days using one continuous loop for both upstairs and downstairs. The radiators farthest from the supply will be getting cooler water compared to the first radiators on the loop. This problem is actually addressed on page 6 of this book. https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf

You may not need the heat exchanger for the radiant loops in your kitchen. Starting on page 24 there is an explanation of how to get two temperatures from one boiler. The lower temperature loops will be on their own zone and will have a separate pump to move the low temperature water thru the floor tubing. No zone valve is necessary if you connect the piping this way.

Also, if you use an ECM variable speed pump that operates on a pressure differential. Then you can eliminate the pressure differential valve.

This is very close to the diagram I have for my son's home. I know this works because I designed it when I lived in that home for over 30 years. The only difference is that in my home, the baseboard zones are actually Hydronic duct coils. That adds a whole new set of controls that you don't need.
I have an easy way to control the system with Wifi Thermostats and zone control panels if you need those plans also.
EDIT: I thought that the check valves could be relocated to the supply side of the baseboard loops. This will control summer overheating caused by gravity flow in a riser pipe. Sometimes it is called "Ghost Flow" and it is briefly explained on page 12. Since you have a zone valve on the return side, you don't need 2 Flo-Control valves. As a matter of fact you don't need one on the water heater loop or the radiant floor loop. I don't even think you need them of the baseboard loop, but it can't hurt in order to solve the overheating issue.

Mr. Ed

hot_rod · July 2023

You only have about 63,000 btu/ hr output to work with. Less if you are above 5000’ elevation

So no part of the system needs more than 1” piping, 6 gpm

All the common zone valves in the 7 Cv range are adequate also

Those copper tube boilers do not like micro, small zones They also need return temperature protection if you have a low temperature zones

Id like to see a primary secondary piping on that boiler to assure adequate flow under low gpm zone conditions. The manual should show the minimum flow requirement for the boiler

mattmia2 · July 2023

The restriction of the zone valves also helps you balance the system.

Note that the id of 3/4" pex is more like 5/8" copper pipe.

The bypass ball valve on the lars is part of the piping diagram from lars and is to protect against low return water temps. A thermostatic valve is better but you need something especially on conventional water tube boilers.

SteveSan · July 2023

@wmarler Please see the attach that explains why the Cv is lower for the 1" Zone Sentry than the 3/4" Zone Sentry valve.

Taco does manufacture Full Port valves for it's Leak Breaker and Potable Water Zone Sentry but that's for open loop systems.

If you have any questions, please give Taco Technical Services a call during normal business hours Mon-Fri 8am-5pm EST 401-942-8000

wmarler · July 2023

EdTheHeaterMan said:
That is a good start.

Thanks! And I really appreciate your notes on my schematic.

hot_rod said:
You only have about 63,000 btu/ hr output to work with. Less if you are above 5000’ elevation

Oh, interesting. We're in Denver so right about 5k' elevation, and according to the model number we have the "I = (5,001 - 8,000) Natural and Propane" model boiler. How did you arrive at the 63k BTUh figure? It sounds like I might have to look at the next size up boiler sooner rather than later :-/.

EdTheHeaterMan said:
Separate zones for the upstairs and the downstairs will surly solve the trouble you have with the inability to heat on very cold days using one continuous loop for both upstairs and downstairs. The radiators farthest from the supply will be getting cooler water compared to the first radiators on the loop. This problem is actually addressed on page 6 of this book. https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf

Thanks for the confidence boost that separate zones will help. I never actually measured temperatures on the returns last winter, which maybe I should have. However, I don't have a recollection that the heating elements at the end of the loops were noticeably cooler than at the start.

... and that's because, I think, that my total length of baseboard heaters in the house is 62'. I had never thought to measure before reading the Zoning Mad Easy Reference Guide :-/. Anyway, I have 28' of 3/4" baseboard elements upstairs and 34' of baseboard elements downstairs. So by the rule of thumb calcs, the system *should* have been capable of delivering 40k BTUh into the house.

Of course if the HWH were calling for heat then I would expect the lion's share of the boiler's output to be going to it. The HWH would have been capable of taking 80k BTUh from the boiler via its 1" connection (and ya, I get that it didn't take 80k BTUh from a system that could only output 63k; what I'm saying is that it probably took 75% or 80% from the boiler, leaving 25%-20% to go to the baseboards). That still doesn't explain why the system could run all night and not get the house warmer than 62° though :-(.

Is it typical for systems to be so undersized? Ultimately what seems to be happening here is that most of the time it's fine, but on those really sustained cold periods, the boiler just isn't big enough for the baseboard runs + HWH together.

And then there's this bit:

mattmia2 said:
The bypass ball valve on the lars is part of the piping diagram from lars and is to protect against low return water temps.

Yea, I read that in the manual. It actually says that a "full-sized 1-1/4" bypass with balancing valve is required when the boiler is installed without primary-secondary piping in a multiple zone system or when the return water temp can be expected to be lower than 120°F," and that "all precautions must be taken to ensure that a maximum temperature rise through the boiler does not exceed 30°F."

But I didn't really absorb it. I had thought the bypass valve was more to do about not having a circulation path if the pump were on but none of the zone valves were open, so I thought I had covered my base using the differential pressure bypass switch.

In retrospect I'm not really sure why I thought that, it says right there in black and white this is a boiler-temperature concern :-/. Anyway, now I'm wondering what my ΔT across the boiler was on my really cold days.

I also think I understand how this ball-valve bypass should have been tuned: on the coldest day of the year right after someone ran a bath & took a shower (so the heat load on the boiler is at it's maximum), I (or my installers) should have looked at the ΔT across the boiler and closed/opened the valve until the diff was 30°. Is that right? [I know they didn't do that, and neither did I].

Could you explain a bit more how to use a thermostatic valve and/or suggest one for me to use? I think I understand the concept: the hot water supply is connected to the cold water return via this thermostatic mixing valve, and a temperature-sensitive element in the valve controls the degree to which the two sides mix. But practically speaking I'm stumbling as I work this out in my head. I found this Thermic Valve? but it seems to operate based on a fixed-value thermostat. Wouldn't I want a mixing valve that opens based on the temperature differential between the hot & cold inputs?

Does someone make a motorized thermostatic valve that opens at an arbitrary ΔT (you know, 30°) taken between two arbitrary points (e.g. temperature sensing units strapped to the boiler inlet & boiler outlet), and closes at another arbitrary ΔT (say, 10°) -- something akin to how a well-pump is controlled by a pressure-sensing switch (e.g. 60/80 Square D?

EdTheHeaterMan said:
Also, if you use an ECM variable speed pump that operates on a pressure differential. Then you can eliminate the pressure differential valve.

Oh, yes, actually my drawing includes an old part number for the circulator. I actually ordered a Taco VR1816 variable speed pump. Do you think it'll work? (Brochure page is here; it has the pump curves).

I'm still not wholly understanding flow rate and head :-/. Here are the Rule-Of-Thumb values for head for my zones:

upstairs baseboard (only, no radiant heat exchanger): 4.8ft (guessing probably 6ft if I include the heat exchanger, but I haven't checked)
downstairs baseboard): 6.0 ft
HWH: 6.6 ft

I think I understand that I want to set the pump to "constant pressure mode" but I'm not sure what pressure differential it's measuring. Does it have a pressure sensor on the discharge side as well as the inlet side, and the difference between the two is the differential? (This would make sense to me). In that case, if I want to design for the maximum flow situation of 16gpm (4 through the 2x 3/4" zones, 8 through the HWH), what setting would I put the pump on -- 5ft, 10ft, or 15ft? I feel really dumb that I'm not getting this, but my first thought was that the 10ft setting is what I'd need to overcome the head requirement of my HWH zone (the zone with the highest head), but this "differential" is twisting me up. If the pump were to supply 10ft of head at its discharge port, and the water flowed just through the HWH loop, then the pump would see 3.4ft of head at its inlet (right? 10ft - 6.6ft = 3.4ft differential). How could the pump ever see 5ft, 10ft, or 15ft of head differential? I think I must be understanding the math here wrong.

... But I'm still glad to hear I can eliminate the pressure differential valve with an ECM pump; I thought that still had to be there to prevent pump burnout if the pump were energized without the zone valves being open, something I thought that could still happen even with the ECM pump.

In order for the ECM pump to work properly do I need to use zone balancing valves like 3/4" NPT QuickSetter Balancing Valve w/ Flow Meter (and the 1" version for the 1" pipe) to make sure only 4gpm go to my 3/4" zones 8gpm goes to the HWH?

EdTheHeaterMan said:
You may not need the heat exchanger for the radiant loops in your kitchen. Starting on page 24 there is an explanation of how to get two temperatures from one boiler. The lower temperature loops will be on their own zone and will have a separate pump to move the low temperature water thru the floor tubing. No zone valve is necessary if you connect the piping this way.

You know, when I was first conceptualizing this I had thought about using a mixing valve to create a my 120° radiant heat zone, but I hadn't thought about using ball valves to restrict flows. I think I'm going to hold with my heat-exchanger idea (I'm probably influenced by the fact that it's already on my work bench and partially plumbed :-/).

EdTheHeaterMan said:
EDIT: I thought that the check valves could be relocated to the supply side of the baseboard loops. This will control summer overheating caused by gravity flow in a riser pipe. Sometimes it is called "Ghost Flow" and it is briefly explained on page 12. Since you have a zone valve on the return side, you don't need 2 Flo-Control valves. As a matter of fact you don't need one on the water heater loop or the radiant floor loop. I don't even think you need them of the baseboard loop, but it can't hurt in order to solve the overheating issue.

I'm pretty sure my current summer overheating problem is not caused by ghost flow -- my baseboard elements both upstairs and downstairs get hot when the HWH calls for heat.

wmarler · July 2023

EdTheHeaterMan said:
Id like to see a primary secondary piping on that boiler to assure adequate flow under low gpm zone conditions. The manual should show the minimum flow requirement for the boiler

Oi, another thing I haven't properly considered

.

Looks like the size-75 Minitherm has a minimum flow rate between 4.8 and 8 gpm, depending on the temperature drop across the boiler. 4.8gpm if the ΔT is 25°F, and 8gpm if the ΔT is 15°F.

Thanks for pointing this out.

I don't know how to proceed at this point :-/.

dko · July 2023

wmarler said:

I don't know how to proceed at this point :-/.

Install primary secondary?

hot_rod · July 2023

It would be good to know what your heat requirement is on a design day. A heat load calculation could help zero in on that number.

You asked:
Oh, interesting. We're in Denver so right about 5k' elevation, and according to the model number we have the "I = (5,001 - 8,000) Natural and Propane" model boiler. How did you arrive at the 63k BTUh figure? It sounds like I might have to look at the next size up boiler sooner rather than later :-/.

Two things to consider in Denver, altitude, less oxygen. And the fuel value of the NG.

For altitude I have always used the industry standard of 4% for every 1000' above 2000' elevation.

So Denver would be a 12% derate.
So 75,000 boiler input X 12%= 66% for the altitude.
The Laars manual should have the derate for altitude number included.

Long time Denver boiler guru Mark Eatherton has a different approach based on the heat load. See attachment.

Assume you have a 66,000 heat load 66,000 divided by .64 = a boiler with a seal level rating of 103,000 btu/ hr.

Timmie @Tim McElwain is our resident gas expert, maybe he will chip in about derating for altitude and watered down NG.

EdTheHeaterMan · July 2023

hot_rod said:
You only have about 63,000 btu/ hr output to work with. Less if you are above 5000’ elevation

Oh, interesting. We're in Denver so right about 5k' elevation, and according to the model number we have the "I = (5,001 - 8,000) Natural and Propane" model boiler. How did you arrive at the 63k BTUh figure? It sounds like I might have to look at the next size up boiler sooner rather than later :-/.

A little at a time we keep getting more information. The altitude issue is something I would never have thought of, I always worked near the coast. Eastern PA., South Jersey, never had to calculate for altitude.

There are 3 BTU number associated with boilers.

1. The input (of 75,000 in your case) is how you size the gas pipe.
2. The Gross output (of 62,000 shown on the chart as heating capacity MBH) is how much heat is available to leave the boiler. Think of it like this: a heater has a 100,000 BTU input. That input happens as a result of a 2000°F flame. The exhaust gas temperature at the outlet of the boiler heat exchanger is 400°F (Just before it goes up the chimney). That means the water in the boiler absorbed 1600° for the available 2000°. That would make the heating appliance 80% efficient. (oversimplified but you get the point). So the gross output is 80,000 BTUh. This number was created in the 1970s in order top make boiler (Water and Steam) and furnace (Warm Air) appliances have a common way to compare efficiency using the AFUE rating (which is based on combustion efficiency and some other factors that make allowances for on and off cycling inefficiencies).
3. The last number is the NET output (52,000 in your case) that only boilers have (not furnaces). This is an arbitrary number of 15% for hot water boilers and 30% for steam boilers to allow for the amount of heat lost by the piping between the boiler and the radiator. This number was selected over 100 years ago by the Institute for Boiler Ratings (I=B=R) which has gone thru several name changes, consolidations and mergers that is now part of the GAMA division of AHRI. (Not important but nice to know where the number comes from). This I=B=R NET number is now shown as NET AHRI on the ratings plates on all boilers manufactured today for sale in USA. This is the number you need to use to compare the actual heat loss with the boiler rating.

After looking at your boiler and seeing that it is actually able to offer you 52,000 BTUh at sea level, then take into consideration the Denver Altitude and what Denver Gas's BTU rating is, you may only have a little over 40,000 BTUh available. And if you can look up the actual BTUh of the Baseboard radiators you have (in leu of using a Rule of Thumb) you may find that your boiler may not handle the addition. A load calculation is needed to determine that. As you mentioned previously, just because a pipe can move 80,000 BTUh does not mean that the 75,000 BTU boiler will make 80,000 BTUh. Same goes for the actual load calculation. If you only require 40,000 BTUh then you don't need to install a larger boiler. If your load calculation shows you that the home with the addition requires 55,000 BTUh, then you will need to account for the cost of a new boiler in your total addition budget.

Taco 1" zone valve reduces to 1/2" internally

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