Weil Mclain GV4 series 2 Condensate Question

[Fletch1]

This is a 23 year old non-condensing boiler. Recently it has begun to create condensate all the time, no matter what the return water temperature is. This boiler runs 180F degree water to baseboard radiators. Flames on at 150F so what's happening with the condensate issue?

 

[Dana]

Flue condensation is one thing, condensation on the heat exchanger plates another.

Where are you seeing the condensation?

Is this the correct model?

 

[Sponsor]

 

[Fletch1]

Flue condensation is one thing, condensation on the heat exchanger plates another.

Where are you seeing the condensation?

Is this the correct model?

Yes that's the beast. I see the condensate drain dripping water all the time. Sometimes you can see water vapor coming out of the drain as it drips water.

 

[Dana]

If I understand it correctly, the condensate drain on this boiler is designed to prevent flue condensation from draining back and collecting inside the boiler jacket. If it's venting into an oversized chimney on an exterior wall or an improperly sized liner there could be more condensate, especially during colder weather. If the flue is obstructed in any way slowing down the stack velocity, that could be a contributing factor as well. The manual specifies a full length liner when installed in a masonry chimney. After 23 years it's quite possible that the liner has failed.

 

[Fletch1]

If I understand it correctly, the condensate drain on this boiler is designed to prevent flue condensation from draining back and collecting inside the boiler jacket. If it's venting into an oversized chimney on an exterior wall or an improperly sized liner there could be more condensate, especially during colder weather. If the flue is obstructed in any way slowing down the stack velocity, that could be a contributing factor as well. The manual specifies a full length liner when installed in a masonry chimney. After 23 years it's quite possible that the liner has failed.

Exhaust vent and air intake are through the wall. Short run less than 6' with no obstructions. When water temp 140F or above there should be no condensate. (At least I don't think there should be as this is cast iron boiler and condensate will eat away at the heat exchanger)

 

[Dana]

A 140F return water temperature does not produce condensation on the boiler plates, but a 140F return water temp doesn't prevent condensation in a flue. Flue condensation is common in gas boilers with combustion efficiencies north of 83% or so. This boiler's AFUE is north of 87%, which delivers VERY cool exhaust temperatures, making it extra prone to flue condensation. Condensing on the heat exchangers begins at about 88% combustion efficiency- this one is right on the edge. But the condensate drain is only there to manage the flue condensation, a necessary feature due to the high efficiency/low exhaust temp.

I assume you're saying it's side-vented, with no vertical stack?

Since yours is set up for direct vent/sealed combustion, did you check to verify there are no mouse nests or other build up on on the air intake piping restricting flow?

 

[Fletch1]

A 140F return water temperature does not produce condensation on the boiler plates, but a 140F return water temp doesn't prevent condensation in a flue. Flue condensation is common in gas boilers with combustion efficiencies north of 83% or so. This boiler's AFUE is north of 87%, which delivers VERY cool exhaust temperatures, making it extra prone to flue condensation. Condensing on the heat exchangers begins at about 88% combustion efficiency- this one is right on the edge. But the condensate drain is only there to manage the flue condensation, a necessary feature due to the high efficiency/low exhaust temp.

I assume you're saying it's side-vented, with no vertical stack?

Since yours is set up for direct vent/sealed combustion, did you check to verify there are no mouse nests or other build up on on the air intake piping restricting flow?

Correct, no vertical stack. No nests in air intake or flue. There were 3 live crickets at the base of the air intake just behind the side panel jacket. In the flex hose that leads to blower. Thanks for your help with this matter Dana. I am more comfortable with the condensation now. Odd that I don't recall seeing it past years.

 

[Dana]

At 23 years this boiler is nearing end of life, and it doesn't hurt to have figured out the range of replacement options ahead of time. At 92,000 BTU/hr of nameplate DOE output the GV-4 is 2-3x oversized for most houses in CT, and if the heating system is broken up into zones it's probably ridiculously oversized for the amount of baseboard on any single zone.

Typical 99% design temp heat loads for average 2000-2500' houses in CT are in the 25,000-45,000 BTU/hr range, depending on age & condition. 3x oversizing is an all too common condition in our region, which ends up hurting both efficiency and comfort. AFUE testing assumes a single zone and 1.7x oversizing. ASHRAE recommends no more than 1.4x oversizing. So if your actual heat load at the 99th percentile temperature bin is 35,000 BTU/hr, you're better off with a boiler with an output of 1.4 x 35,000= 49,000 BTU/hr, not 92,000 BTU/hr. It'll have enough oversizing factor to cover the record low temps with margin, and have reasonable recovery times from overnight setback.

A cast iron boiler needs a minimum of 5 minute burn times to near hit near it's nameplate AFUE efficiency (10 minutes is even better.) Try monitoring burn times under a number of load conditions (all zones calling for heat, one zone only, etc.) If it turns out that it's short-cycling it may be worth installing a retrofit economizer controls to mitigate that. If it's 3x oversized and short-cycling you could see a double-digit percentage reduction in fuel use with a retrofit economizer control. But as long as it's working reliably and not leaking there's no rationale for retiring it early. If it's getting detectable flue condensation that means it's probably still hitting at least 84-85% combustion efficiency (steady-state) despite being old enough to have voted in the last national election. (Hopefully it's not registered to vote. )

A mid winter gas bill, the exact meter reading dates & fuel use, and a zip code (for weather data and outside design temperature) would be enough to put an upper bound on the actual heat load, unless you're supplementing the with a wood stove or something, or spent a week in Belize with the thermostat turned down to 50F while you were away.

Other considerations for the replacement would be the number of zones, and the amount of baseboard on each zone.

 

[Fletch1]

At 23 years this boiler is nearing end of life, and it doesn't hurt to have figured out the range of replacement options ahead of time. At 92,000 BTU/hr of nameplate DOE output the GV-4 is 2-3x oversized for most houses in CT, and if the heating system is broken up into zones it's probably ridiculously oversized for the amount of baseboard on any single zone.

Typical 99% design temp heat loads for average 2000-2500' houses in CT are in the 25,000-45,000 BTU/hr range, depending on age & condition. 3x oversizing is an all too common condition in our region, which ends up hurting both efficiency and comfort. AFUE testing assumes a single zone and 1.7x oversizing. ASHRAE recommends no more than 1.4x oversizing. So if your actual heat load at the 99th percentile temperature bin is 35,000 BTU/hr, you're better off with a boiler with an output of 1.4 x 35,000= 49,000 BTU/hr, not 92,000 BTU/hr. It'll have enough oversizing factor to cover the record low temps with margin, and have reasonable recovery times from overnight setback.

A cast iron boiler needs a minimum of 5 minute burn times to near hit near it's nameplate AFUE efficiency (10 minutes is even better.) Try monitoring burn times under a number of load conditions (all zones calling for heat, one zone only, etc.) If it turns out that it's short-cycling it may be worth installing a retrofit economizer controls to mitigate that. If it's 3x oversized and short-cycling you could see a double-digit percentage reduction in fuel use with a retrofit economizer control. But as long as it's working reliably and not leaking there's no rationale for retiring it early. If it's getting detectable flue condensation that means it's probably still hitting at least 84-85% combustion efficiency (steady-state) despite being old enough to have voted in the last national election. (Hopefully it's not registered to vote. )

A mid winter gas bill, the exact meter reading dates & fuel use, and a zip code (for weather data and outside design temperature) would be enough to put an upper bound on the actual heat load, unless you're supplementing the with a wood stove or something, or spent a week in Belize with the thermostat turned down to 50F while you were away.


Other considerations for the replacement would be the number of zones, and the amount of baseboard on each zone.

I and a friend installed this. I could have bought a the next size down, but I wanted to be sure I had a big enough one for this 1600 sq ft house. my 1st mistake. So yeah, lots of nut in this boiler. 2nd mistake , went zone crazy, if you count the indirect there are 7 zones. Currently only 4 zones are being used and only 3 of those heavily. Zone 5 will soon be placed in service (bathroom) high heat loss due to skylight and fan, very small zone only 6 ft of Runtal radiator but it will only be occasionally and when the other zones are on so I don't think it will cause short cycle. No supplemental heat source here. I think when the time comes I will replace this boiler with another cast iron one like the WM GV90+. I've done well with my current boiler, it owes me nothing.

 

[Dana]

A typical 1600' insulated 2x4 framed house in CT with clear glass storm windows (no low-E) will have a heat load of ~22-25,000 BTU/hr if the foundation is insulated, maybe 30-35,000 BTU/hr without foundation insulation. A 1600' house built to IRC 2012 code min will have a heat load of less than 20,000 BTU/hr. Even the GV-3 is more than 2x oversized for the whole house load, and is insanely oversized for the radiation on the individual zones.

When you micro-zone the hell out of it any one zone is going have far less radiation output than boiler the boiler is dumping into the system, leading to a high potential for short-cycling, even if the total amount of radiation in the house can deliver the full boiler output. Time the burns- I'd be surprised if it's averaging more than 2-3 minutes per burn, and it's probably doing a dozen or more burns per hour. If you're keeping the boiler for a few more years, a retrofit heat-purging economizer will likely deliver more than 10%, possibly more than 15% fuel savings, by maximally utilizing the thermal mass of the boiler to lengthen the minimum burn times, and reduce the raw numbers of ignition cycles.

At your whole house heat load if you keep the micro-zoning you'll probably be much better off changing the system topology, and go with a "reverse indirect" buffering the boiler rather than an indirect operated as a separate zone. Slave the boiler to serve only the tank's call for heat, and letting the zone thermostats draw heated water from the buffer, not directly from the boiler. Even the smallest reverse indirects have about an order if magnitude more thermal mass than a 2 or 3 plate boiler.

If your current indirect fails before the boiler does, that would be a good time to consider reconfiguring the system to deal with it.

Some of the new mid-efficiency cast-iron boilers already come with heat-purging controls. The Burnham ESC-3 and ES2-3 are ~50K output boilers with heat-purge control, and they're internally plumbed to be tolerant of cool water return (down to 110F) from radiation without excessive condensation.

If you're going for a condensing boiler like the GV90+ it really has to be run at condensing temperatures (return water temps of 120F or less) to get the benefit, which makes the micro-zoning aspect even more problematic. A central buffer tank kept at a much lower temp would be necessary to keep it from short-cycling at condensing temps, with a separately zoned indirect for serving up the domestic hot water.

 

[Fletch1]

I did not realize GV90+ was condensing boiler. I did not research it since I hope replacement is still 2 years away. I don't want a condensing boiler. Only assumed as cast iron it would not be. Started with 66 degree main living area and set thermostat to 70F. First burn 7 min 30 seconds 2nd burn 4 min 30 seconds. House gains temp at 1 to 1.5 degrees per hour in the larger open spaces. Current indirect is new, but when boiler is replaced I will go with a stand alone unit. I was thinking of reverse pipping the upstairs and downstairs bath together but I don't think I want 2 baths on one thermostat. I would need a pro to come and look it over to see the best way to reduce the zone number. Each zone is a home run back to boiler. Everything is buttoned up so changes won't come easy. I've had a few pros out here but it seems they want to sell me a boiler, and always around the same size as I have and always at a must be magic number of 10 grand. Hard to get them to talk about cleaning up my past mistakes. That's why I'm thinking to buy just a regular cast 80% 85% iron boiler and slip it in myself to my existing zone valve array. I could do a smaller boiler to make it work harder, maybe get at least somewhat more efficient. This was a conversion from hot air furnace to hydronic 23 years ago. I replaced all the zone valves 2 years ago and installed shut off valves to make servicing them easier. I understand most of your drawing but not sure what from radiant to radiant means?

 

[Dana]

The initial burn is bringing the thermal mass of the boiler fully up to temp, and with a bigger temperature difference between the water and air near the floor the heat emitters put out more heat than in a steady-state. How much baseboard or other radiation is there on that main living area zone?

With smaller zones (in terms of zone radiation, not floor area) the burn times will be much reduced from that 270 second burn.

Zoning an upstairs room with a downstairs room almost never works well. Zoning whole floors or large portions of floors together can work well if the radiation per room is proportional to the heat losses of the rooms. Keeping the upstairs zones upstairs, and the downstairs zones downstairs is the way to go.

The side-vented sealed combustion 3-plate Burnham ESC-3 has smart enough to controls to be able to get the most out of the thermal mass without buffers. At 52,000 BTU/hr out it would take about 80'+ of fin-tube baseboard to balance boiler output to radiation output with no cycling during calls for heat, but as long as there's at least 40' per zone it's not going to be a short-cycling disaster when utilizing heat purge controls.

There are smaller dumber 2 plate cast iron boilers out there with ~25-35K of output that might possibly work, but most of those are atmospheric drafted, not sealed combustion side-vented.

If you figure out on your own what you need/want you can just specify it and put it out for competitive bid.

The "From Radiant" and "To Radiant" in the Ergomax schematic indicates a lower water temperature zone re-circulating through a thermostatic mixing valve (looks like an inverted T in the diagram, and is not labeled.) It's really just a crude hack of a schematic to demonstrate how it might be used, even in a multi-temperature heating system.

If you did a room-by-room I=B=R spreadsheet type heat load calculation and compared the amount of radiation each of those rooms has, those with comparable load to radiation ratios (within 15% of each other) would usually zone together nicely.

 

[Fletch1]

The initial burn is bringing the thermal mass of the boiler fully up to temp, and with a bigger temperature difference between the water and air near the floor the heat emitters put out more heat than in a steady-state. How much baseboard or other radiation is there on that main living area zone?

With smaller zones (in terms of zone radiation, not floor area) the burn times will be much reduced from that 270 second burn.

Zoning an upstairs room with a downstairs room almost never works well. Zoning whole floors or large portions of floors together can work well if the radiation per room is proportional to the heat losses of the rooms. Keeping the upstairs zones upstairs, and the downstairs zones downstairs is the way to go.

The side-vented sealed combustion 3-plate Burnham ESC-3 has smart enough to controls to be able to get the most out of the thermal mass without buffers. At 52,000 BTU/hr out it would take about 80'+ of fin-tube baseboard to balance boiler output to radiation output with no cycling during calls for heat, but as long as there's at least 40' per zone it's not going to be a short-cycling disaster when utilizing heat purge controls.

There are smaller dumber 2 plate cast iron boilers out there with ~25-35K of output that might possibly work, but most of those are atmospheric drafted, not sealed combustion side-vented.

If you figure out on your own what you need/want you can just specify it and put it out for competitive bid.

The "From Radiant" and "To Radiant" in the Ergomax schematic indicates a lower water temperature zone re-circulating through a thermostatic mixing valve (looks like an inverted T in the diagram, and is not labeled.) It's really just a crude hack of a schematic to demonstrate how it might be used, even in a multi-temperature heating system.

If you did a room-by-room I=B=R spreadsheet type heat load calculation and compared the amount of radiation each of those rooms has, those with comparable load to radiation ratios (within 15% of each other) would usually zone together nicely.

 

[Fletch1]

About 56 ft of base board in the upstairs living area. Master BR has 12' . Downstairs zone is 23' of radiator. All 3 zones were on during the 1st burn and probably the 2nd burn. The Ergomax 23 cost is about $1450, that does not sound too bad. . The 2 bedrooms that are on their own zone are the same size so one idea is to disconnect electrically one zone valve and leave it manually open so that when the master bedroom calls for heat the other BR will also heat. What ya think? . New problem though boiler has locked me out twice tonight.

EDIT 01/19 07:38 AM... Boiler ran OK through the night with no lockouts.

 

[Dana]

I've seen the E23 priced under $1000 in recent years as well as it's nearest equivalent the Turbomax T-23 . I picked up a scratch & dent E44 for about $700 when shopping around after deciding to micro-zone my place. Everhot EA 8-50 is comparable, typically around a grand.

Without the full schematic of the system it's hard to say what the easiest way to combine zones is, but it sounds like you're on the right track.

On a zone with 56' of zone baseboard that's emitting maybe 30-35,000 BTU/hr and a boiler that's putting 92,000 BTU/hr in it's definitely going to cycle. Setting the temperature differential on the aquastat controls as high as possible and bumping up the output temp will increase the minimum burn times, reducing the number of burn cycles. With heat-purging economizers you can set the programmed low temp to 130F with a boiler like this, and let it run the high-limit to whatever the safety max on the boiler is, which is usually a much bigger swing than you can get with aquastat controls. Heat purging economizers also "learn" to predict the end of a call for heat and cut the burners early, letting the stored heat in the boiler finish the call for heat to reduce standby losses (the boiler loses less heat when it's parked at a lower temp during idle), and purges heat from the boiler on a new call for heat until it reaches the programmed low-limit.

 

[Fletch1]

I've seen the E23 priced under $1000 in recent years as well as it's nearest equivalent the Turbomax T-23 . I picked up a scratch & dent E44 for about $700 when shopping around after deciding to micro-zone my place. Everhot EA 8-50 is comparable, typically around a grand.

Without the full schematic of the system it's hard to say what the easiest way to combine zones is, but it sounds like you're on the right track.

On a zone with 56' of zone baseboard that's emitting maybe 30-35,000 BTU/hr and a boiler that's putting 92,000 BTU/hr in it's definitely going to cycle. Setting the temperature differential on the aquastat controls as high as possible and bumping up the output temp will increase the minimum burn times, reducing the number of burn cycles. With heat-purging economizers you can set the programmed low temp to 130F with a boiler like this, and let it run the high-limit to whatever the safety max on the boiler is, which is usually a much bigger swing than you can get with aquastat controls. Heat purging economizers also "learn" to predict the end of a call for heat and cut the burners early, letting the stored heat in the boiler finish the call for heat to reduce standby losses (the boiler loses less heat when it's parked at a lower temp during idle), and purges heat from the boiler on a new call for heat until it reaches the programmed low-limit.

The aquastat on this boiler is a fixed 30 degree swing, I always thought it should at a 40 degree. I think probably the best thing to do is leave things as they are though this winter. Cozy warm here even if were not the most efficient house on the street. The Burnham you mentioned seems to have a nice footprint and may be the way to go. If I were to go with a boiler such as the Burnham, would pairing it up with the Ergomax be a good way to go? Or would that be overkill? I'll do the research and replace the Weil McLain before it craps out. Probably late summer. Thanks for all your help. I really do appreciate your sage council.

 

[Dana]

With a 52K output boiler and 56' of baseboard the burn times would be reasonably long, especially since it comes equipped with heat purge control.

But if the other zones are all 20 footers (or shorter) it would still benefit from having more thermal mass to work with.

Seriously, since you have plenty of time, build yourself a spreadsheet, and run your own room by room heat load numbers based on construction, and see if you can't consolidate some zones. For a primer on how that's done, try this bit o' bloggery. For purposes of figuring out the ratio of radiation to load high precision is not required. You can just use +10F for the outside design temp, and 70F for the interior design temp (a temperature difference of 60F), and ignore the infiltration losses. If you shared a bit with how your walls are constructed & insulated, the window types (including storm windows), and attic insulation etc, I could cook up reasonable U-factors to use for the calculation. The basic calculation for each exterior surface type is:

U-factor x square feet x temperature difference = BTU/hour.

Add up the square feet of window in the room, run the arithmetic, the total square feet of wall area (subtracting out the windows & doors) , run that arithmetic, the total amount of top floor ceiling, run the numbers, and add it all up. Then divide the room total BTU/hr by the linear feet of baseboard in that room.

For instance, say you have R30 in the attic (a U-factor of about 0.04), and 2x4/R13 walls (U-factor of about U0.10) and wood sash double hungs with clear glass storm windows (about U0.50) . A 10 x 15 corner room with 9' ceilings and three 10 square foot windows has 30 square feet of window, 195 square feet of wall, and 150 square feet of ceiling, and let's say it has 14' of baseboard.

Window losses:

U0.50 x 30' x 60F= 900 BTU/hr

Wall losses:

U0.10 x 195' x 60F= 1170 BTU/hr

Ceiling losses:

U0.04 x 150' x 60F= 360 BTU/hr

Add it all up the total conducted loss comes to: 2430 BTU/hr

Load to baseboard ratio: 2430/14= 174 BTU/hr per foot of baseboard.

If other rooms have similar ratios, with the highest being within 15% of the lowest, they will tend to track OK when zoned together. So if that 174 is the middle number, rooms with ratios between roughly 160 BTU/hr per foot and 190 BTU/hr per foot would work OK operated as a single zone, but a room that came out at 280 BTU/foot-hour would run cold, and a 120 BTU/foot-hour room would run warm if lumped into a zone with a ratio of 175 BTU/ft-hr.

Sometimes it's worth adding or subtracting a bit of radiation from a room to make it work well. Most people prefer the bathrooms to be a bit warmer, and bedrooms a bit cooler, and that can be factored in a bit too.

For a 52,000 BTU/hr output boiler like the Burnham ESC-3 it's worth having at least 50' of baseboard per zone if you can, and more is definitely better. If That's simply not possible otherwise you can go with a Turbomax or something kept at 160-180F and keep the micro-zoning. Unless you have a monster-sized spa to fill, a 28-30 gallon reverse indirect kept at 160F+ with 52K of burner behind it would be good enough for most homes. (I have a 48 gallon Ergomax, which is somewhat marginal on tub-filling hot water performance due to the fact that I'm running it at ~125F, not 180F. But in combination with a drainwater heat exchanger it is enough for effectively endless showering capacity, even with all zones calling for heat.)

 

[Fletch1]

I don't recall telling you about windows. But I have all fairly new Anderson new construction type windows (not storm windows) and probably more like R40 in the attic. A new bow window in the living room. No fancy gases and just the double pane glass. 8' ceilings. The downstairs zone is 22' radiator and the downstairs bath when complete will add about 6' (28') upstairs there are two 12' zones which is why I asked if you thought it would be a good idea to just manually leave one zone valve open so that zone would heat whenever the master bedroom heated? I'll try to do the calc's but will get back to you with measurements .

 

[Dana]

Clear glass double panes don't meet current code minimums in CT, but almost any low-E double pane does. If they're new windows you probably have (or can look up) the manufacturer's specified U-factors in the documentation somewhere. If low-E, presume U0.35 as the worst-case which has been code-min in CT since at least a decade ago. (Current code is U0.32 max). If it's truly uncoated non-low-E clear glass wood or vinyl assume U0.50.

When you say "...22' radiator...." is that some large chunk of cast iron with some real water volume, or are you talking fin-tube baseboard? (It makes a difference on burn times due to the substantially higher thermal mass.)

What's the material stackup of the walls, from the interior paint to the exterior paint, including the insulation thickness & type, and the siding type?

R40-ish blown insulation in 2 x 12 joists with 16" o.c. spacing it's about U0.026. If 24" o.c. spacing make that U0.025.

If it's 2 x 10 joists and the joists are buried by a couple of inches call it U0.022 (at either spacing).

If 24" o.c. trusses with 2 x 4 bottom chords use U0.018.

 

[Fletch1]

Sorry I was not clear, the windows are low E double pane vinyl clad over wood frame. Attic is fiber glass batts between 24" OC trusses and then another layer ran in along the length of attic space to R38 or better. House built in 1964 is 2x4 walls R13 fiberglass.. Ceder shingles over some sort of creosote black material and some sort of brown matting. This house baseboard radiator throughout. Downstairs where the 22' of base board is below grade by varying amounts. Cement block foundation R13 fiberglass. The composite bow window met the $1500 energy credit that was around a few years back. It is Okna by Starmark. Sliding 8' French door Anderson, same low E double pane. Aprox 3'x5' low E casement in kitchen. Each of the 3 bedrooms has 2 double hung 2.5' x 3' low E windows. Downstairs 8 older double hung low E windows. Just slightly smaller than the upstairs windows. The 2 bathrooms when set up the way on want them will have 6' baseboard radiator one will be a Runtal useing 1/2" HE pex back to the zone valve. Not quite sure how much trouble that adds to the mix. . On the plus side the downstairs bath will have it's 6' of rad tied into the 22' making for 28' of baseboard. This house is a much tighter house than when the boiler was put in service 23 years ago. Oh yeah, the bow window is 56" x 90".