Replace Zone Valve or Whole System + Help Spec a New Boiler

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Reicherb

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I have a Well-McLain Series 3 P-D--7 boiler that I believe to be original to the house which was building in 1968. It's not very efficient and I learned this morning that one of the zone valves is stuck open causing the circulation pump to run constantly (I beleive it's actual been this way since we moved it. No wonder our electrical use is so high...) It's the baement zone which we don't use much for living space so I've disconnected the zone valve for now.

My question is. Do I replace the valve or do I make it to warmer weather and replace the whole system? I don't know how much more efficient new system are nor Do I know exactly what a new system would cost. The only maintenance history I see is that the two working zone valves were replaced in 2008.

I have enough plumbing and electrical skill that I could do the installation once I assessmbled the appropriate part list.

So, do I replace the valve or replace the whole system? Please let me know what information I'm leaving out that would help answer my question.

Thanks,

Brad
 

Tom Sawyer

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Lol, than replace the zone valve head. Have the boiler serviced by a professional that understands how to optimize its performance. Truthfully, though that boiler is 50 years old, Weil McLain still manufacturers boils that are pretty much the same as yours with updatd burners and smart controls.
 

Reicherb

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Ok, let's try this a different way...

Is the added efficiency of a boiler that is basically the same but with updated burners and controls (doesn't that make it totally different?) worth the cost to replace it?

I had the boiler inspected 18 months ago and was told that it was working fine but should be replaced because it's so ineficient.
 

Dana

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Replace the zone valve now- it's comparatively cheap, and will probably still be used in the system even if you swap out the boiler.

Any boiler on the verge of being old enough to be receiving it's own AARP solicitations is worth thinking about replacing. Before heading down that road it's important to get a handle on your actual heat load at the 99% temperature bin (probably 0-5F in your location, even though it's sometimes well into negative digits there) so that you don't end up with something so ridiculously oversized that it impacts efficiency or longevity. When new the Well-McLain Series 3 P-D-7 has (or had, when new) a steady-state output of 120,000BTU/hr, which is about 3-4x the design heat load of a typical 2000-2500' 1960s vintage houses in US climate zone 5 (that's you), assuming at least some updates to the windows (got storm windows?) and maybe some retrofit insulation since the house was built. It's probably more than 2x the heat load it had to serve before any upgrades.

This level of oversizing would be bad for efficiency even with a brand new boiler, and the last thing you'd want to do is replace it with a boiler of the exact same output. People worry about undersizing, but 2x oversizing would mean you're still good for temps of -60F or lower, a temp not seen in Linden MI since the last ice age. Right-sizing it (to something only 1.25-1.5x oversized) would deliver both higher comfort and less wear & tear on the system components, and would still have sufficient margin for the Polar Vortex events.

If you have a mid-winter gas bill with exact the meter reading dates and the amount of fuel used, we can use the 80% nameplate efficeincy of the beast to determine a firm upper-bound on your heat load. To do this we need a ZIP code to look up the heating degree-day data on the nearest weather station at degreedays.net. With fuel-use per heating degree day it's 5th grade arithmetic to come up with a output-BTU per degree-hour constant. Multiply that constant times the difference between 65F (the heating degree-day base), and your 99th percentile temperature bin, and you end up with the BTUs per hour you need to stay warm at that temp. This is fairly crude when done on a single month- maybe a 10-15% error. But since the boiler isn't really achieving getting 80% efficiency after 47 years of service (and you probably use gas for other things like hot water), it's really an upper bound. Oversizing from there by 25% would be plenty of margin.

Don't be surprised if the fuel use against HDD calculation tells you that you only need 30-40,000 BTU/hr of boiler output. Older (or even newer) boilers that are 3x oversized for the load are (sadly) pretty typical.

From there we can discuss other system factors of note, such as the total number of zones, the amount of radiation on each zone, etc., which are important factors for figuring out exactly what to replace it with.
 

Reicherb

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Thanks Dana!

We have a 2400 sq/ft home (according to the realily people).

Here is a chart of meter reads.
Read Type
Date
Meter Read
Estimated Feb 2, 2015 3653
Actual Jan 2, 2015 3396
Estimated Dec 1, 2014 3184
Actual Oct 31, 2014 3059
Actual Oct 1, 2014 2999
Actual Sep 2, 2014 2965
Actual Aug 2, 2014 2942
Actual Jul 3, 2014 2918
Actual Jun 4, 2014 2888
Actual Jun 3, 2014 2888
Actual Jun 3, 2014 2888
Actual May 2, 2014 2839
Actual Apr 3, 2014 2752
Of course they estimated the use most of the winter...

We do have a gas hot water heater and gas dryer.

We have 3 zones. 1 per floor. The heating system is entirely baseboard fin tube. do I simply measure the number of feet of fin tube on each floor?

Thanks again!

Brad
 

Dana

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I assume those readings are the CCF read right off the meter, not actual usage. They probably have the BTU/CCF buried somewhere in the fine print (it varies by natural gas source), but a typical average would be 102,500 BTU/CCF.

Between 1 October and 2 January you used (3396-2900=) 397 CCF, times 102,500= 40,692,500 BTU

If we generously assume that the thing is delivering 75% combustion efficiency even at this age, that's 0.75 x 40,692,500 = 30,519,375 BTU that went into the heating system plumbing (the rest went up the flue.)

If we use the Howell, Livingston County Airport weather station data to make a daily HDD spreadsheet, down load it and add up the HDD from 1 October through 1 January (not 2 January, since it wasn't done yet when they took the reading), it comes up with 2505.1 HDD.

30,519,375 BTU /2505.1 HDD = 12,183 BTU/ HDD

So using 24 hours in a day, that 12,183 BTU/24= 508 BTU/ degree-hour.

If we use Flint's 99% outside design temp of +3F, from a base-65F balance point that's 65F-3F= 62 heating degrees.

Which implies a heat load of about 508 BTU/degree-hour x 62F degrees= 31,496 BTU/hr @ +3F. If by some miracle the thing is actually delivering 80% efficiency the implied heat load is still only 31,496 x (80/75 )= 33, 596 BTU/hr, not a big difference. Your real load is probably closer to 30K @ +3F (unless you spent December in Cancun with the thermostat set to 55-60F rather than living in the house for that stretch. :) )

And that's pretty much an upper bound: You were also using gas for hot water (with a stand-alone tank, or something else), the dryer, etc. and the thing may actually be delivering less than 75% AFUE type efficiency. But if you up-sized it from there by 1.25x to about 40K, you'll have PLENTY of margin against extreme coolth. At that output you would be covered for 40,000 BTUh /508 BTU per degree-hour = 79 heating degrees, so it won't even think about losing ground until it's 65F - 79F= -14F .) The original boiler's 120K output when new is about 4x oversized for your actual load.

As a sanity check, 31,496 BTU/2400'= ~13 BTU/hr per square foot of conditioned space. That's credible for a reasonably tight batt-insulated 2x4 framed house with decent storm windows or code-min insulated glass replacement windows and R30 in the attic. A lot of houses that size might come in at 15 BTU/ft, a totally leaky house with single-panes and almost no insulation might come in at 20-25BTU/ft.

So, go ahead and measure up how many feet of baseboard you have on each zone, by zone, and we can run some different napkin-math there.
 

Reicherb

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You're awesome!

We replaced all of the windows this summer and added insulation to the attic. The walls have blown in insulation added after the house was built so I'm sure it's not perfect. I'll get you some baseboard measurements as well.

One note is that there is an addition on the first floor that isn't very warm probably because it doesn't have enough baseboard and probably because it's over a crawl space. We'll be remodelling that area at some point. It's a mud room and bathroom. I may consider adding infloor radiant heat.

Measurements to come.

Thanks for all of your help!

Brad
 

Reicherb

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The basement has 28' of baseboard and a 10x10 room has none so I'll eventually add some where.

The 1st floor has 60' and already described what needs to be added in the addition. The kitchen also has none as the outside walls all have cabinets on them. I'm not sure if I should add anything there. It's not cold.

The 2nd floor has 80' and seems to be appropriate.

Each floor is on it's own zone.

Thanks,

Brad
 

Dana

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So you currently have 168' of fin-tube for 120,000 BTU/hr of total boiler output, or ~715 BTU/ft-hr. (See typical fin-tube output tables for reference.) The heat emission output from the fin-tube balances with at an average water temp (AWT) of ~200F, so even with the whole-house operating as a single zone the radiation is slightly undersized for the current boiler. The 28' zone is CRAZY undersized for the boiler, and it's burn cycles will be numerous & brief while serving that zone only, cutting into efficiency and putting wear & tear on the boiler.

If you dropped back to a direct-vented 3-plate cast iron 85% efficiency beastie like the Burnham ESC3 with 60K of output you'd still be close to 2x oversized for the actual heat load, but at ~36o BTU/ft the whole-house radiation would balance with the boiler output at an AWT of about 140F which is fine. For just the single 28' zone calling for heat you're looking at about 60,000 BTU /28'= 2140 BTU/ft, which is still in crazy short-cycling territory. The 60' zone is at 1000 BTU/ft, which doesn't really balance, but it probably won't go nuts on short cycles when serving that zone only, since there is at least some thermal mass to the system. The 80' zone is at 750 BTU/ft, which would balance at ~2o5F AWT, which pretty much balances if you set the high-limit on the boiler to 220F.

There are some mid efficiency 2-plate atmospheric drafted boilers like the Weil McLain CGa25 with 44K of output. The whole-house radiation would be 44,000/168'= 260 BTU/ft, which balances at an AWT of 130F. That could work, but you would need to be sure to install a bypass branch at the boiler to keep the water entering the boiler at 130F or higher to avoid damaging condensation on the boiler plates. You would also need a narrowing stainless liner to the flue to avoid destroying the chimney with condensation. It would balance at reasonable temps on the 60' & 80' zones, but at about 1600 BTU/ft it would still short-cycle on the basement zone, but not nearly as badly as the current boiler does.

If you stepped up the efficiency to a ~95% AFUE modulating condensing boiler, a 50K-in/47K-out unit like the Peerless PF50 could work. (There are at least a half-dozen other similar sized pretty-good mod-cons in that range that could work). The min-fire output of that thing is about 15,000BTU/hr. One the 60' zone that's 250BTU/ft, which balances at an AWT of 125F, which means it will operate in the condensing temperature zone (= sub-125F return water entering the boiler) without short-cycling, as would the 80' zone. On the 28' zone you're still looking at 535BTU/ft, which would only balance at ~170F AWT, well above the condensing zone, but as long as it isn't short-cycling on all zones, that's probably going to be OK. If need be you may be able to fix short cycling on the basement zone with more radiation (another 30' of fin-tube is pretty cheap, if there's room for it) or by higher-mass radiation. The min-fire output of the thing is about your average winter load, so if you use the outdoor reset temperature controls (which raises & lowers the output temp of the boiler in response to the outdoor temp), once you tweak-in the temperature curves it would run in condensing mode almost all the time, and won't short-cycle (much).

Under outdoor reset you would max out the efficiency by dialing in the curve so that the burns are at a nearly 100% duty cycle whenever it's cold out, and dispense with thermostat setback strategies, since setbacks require higher water temps (= lower efficiency) for the recovery ramps. That would also almost guarantee that calls for heat from the basement zone would overlap calls from the other zones, limiting the amount of short-cycling you would see.

If going for a mod-con it's important to look at the min-fire output, since that determines the short-cycling potential. Anything with a min-fire input much higher than about 16,000 BTU/hr would not be appropriate for your radiation & loads, since it's output would be more than your average winter load, and it would put you in short-cycling territory on your smaller zone.

With any new boiler it's worthwhile considering adding an indirect-fired hot water tank as an other zone, since that increases the duty-cycle on the boiler (which increases it's AFUE), and when operated as the "priority zone", the water heater would have higher performance than most standalone tanks even with a tiny ~50K input/82% 2-plate cast iron boiler. The net hot water heating efficiency will be higher than any non-condensing tank water heater too.
 

Dana

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If opting for a high mass gas-fired system w/ domestic hot water I'd take an HTP Versa over a System 2000. An HTP can't short-cycle on any sized zone, and has higher combustion efficiency and even lower heat-stranding than the Sys2K, and takes less space. (If oil-fired the Sys2K is about as good as it gets though.)

after.jpg
Versa Flame

Cindy%27s%20system%202000.JPG
System 2000
 
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