Mod CON? Or Power vent 85%?

Suzook

Converting from oil to gas. Have a couple of options. I can get a burnham 94% mod con for $600 after rebates, or a power vent "old school" for $1000. Either one will have an indirect for HW. I have slant fin baseboard, which I have heard wont make the mod con condense properly. I still have heard good results though. I have 2 zones. 1st floor has 50k BTU of fin(100ft) and 2nd floor has 25k BTU of fin(50 ft). Thoughts??? I feel like going with the modcon as I believe it will condense at times, but even when its not, will still be at about 88%. Its also cheaper. Would like some honest thoughts....BTW, I am not reusing the old chimney, hence the power vent model.

GW

Old school is kinda simple, condensing units need more professional hands on for proper set up. Pros and cons for everything

gschallert

Suzook said:

I have slant fin baseboard, which I have heard wont make the mod con condense properly. I still have heard good results though. I have 2 zones. 1st floor has 50k BTU of fin(100ft) and 2nd floor has 25k BTU of fin(50 ft). Thoughts???

Baseboard not working with modcon's is a generalization that can't really be used as such. It depends on how much baseboard you have and if your emitter capacity exceeds your heat loss. You have 75k of emitter (roughly) so what is your heat loss? My in-laws went with a modcon and finned baseboard and it's heating their house no problem with 130 degree or less avg SWT and condensing almost all the time. They have about 30% more emitter capacity than their heat loss on design day. If you get down into the area where heat loss and emitter output are close you lose the condensing aspect (because you have to supply higher water temps) but you still have burner modulation which can be worthwhile on its own for fuel savings.

Suzook

gschallert said:

Suzook said:

I have slant fin baseboard, which I have heard wont make the mod con condense properly. I still have heard good results though. I have 2 zones. 1st floor has 50k BTU of fin(100ft) and 2nd floor has 25k BTU of fin(50 ft). Thoughts???

Baseboard not working with modcon's is a generalization that can't really be used as such. It depends on how much baseboard you have and if your emitter capacity exceeds your heat loss. You have 75k of emitter (roughly) so what is your heat loss? My in-laws went with a modcon and finned baseboard and it's heating their house no problem with 130 degree or less avg SWT and condensing almost all the time. They have about 30% more emitter capacity than their heat loss on design day. If you get down into the area where heat loss and emitter output are close you lose the condensing aspect (because you have to supply higher water temps) but you still have burner modulation which can be worthwhile on its own for fuel savings.

Heat loss is about 60K, I figure even if it doesn't condense all the time, its still slightly more eff than the 85% unit. Its also cheaper.

gschallert

With those numbers you could probably condense most of the heating season, all but design days and adding in modulation cost savings on top of installation cost savings.....seems like an obvious choice to me. I replaced an old Burnham CI boiler with a WM CI boiler last year but only because I needed to save money to install a mini-split system for A/C & shoulder season heating this year. If I didn't need the A/C I would probably have gone with a modcon and I'm a bit jealous of my in-laws who like you converted from oil to gas and went with a modcon combi. Their heating bills dropped by 75%.

HVACNUT

Do you have an existing gas service.
If so, do you need a larger meter and new piping throughout to compensate for the new boiler?
Permits?
I'm just a dumb oil guy, but a 3 pass high efficiency, cold start boiler, an indirect and ODR might be worth looking into. Soot and odor are things of the past with a properly installed system.

Suzook

HVACNUT said:

Do you have an existing gas service.

If so, do you need a larger meter and new piping throughout to compensate for the new boiler?

Permits?

I'm just a dumb oil guy, but a 3 pass high efficiency, cold start boiler, an indirect and ODR might be worth looking into. Soot and odor are things of the past with a properly installed system.

Nope, no existing gas service. They are bringing it in this month. I'm so done with oil, sorry, but its just a nuisance in so many ways. Gas is cheaper, and I expect to recoup my expenses in 6 or 7 yrs. Then its all gravy, along with none of the smelly, sooty, disgusting oil.

Zman

HVACNUT said:

Do you have an existing gas service.

If so, do you need a larger meter and new piping throughout to compensate for the new boiler?

Permits?

I'm just a dumb oil guy, but a 3 pass high efficiency, cold start boiler, an indirect and ODR might be worth looking into. Soot and odor are things of the past with a properly installed system.

You can run the numbers using your local rates and the attached spreadsheet.
In most markets natural gas is way cheaper than oil when compared as cost per Btu.

HVACNUT

Yeah yeah, I know.
My pillow is a Riello F5.
I love it and no, I'm not a dealer.

Zman

To the original question,I think you have good application for a mod con. If you want to figure out how often it will condense, do a heat loss calc for your design day, then change the outdoor temp to your typical day. You can then look at the output tables for your baseboard and find out what water temp you will need.

I don't have first hand experience with the Burnham mod con. I do like the design of the Firetube K2 over the Alpine.

Suzook

> @Zman said:
> To the original question,I think you have good application for a mod con. If you want to figure out how often it will condense, do a heat loss calc for your design day, then change the outdoor temp to your typical day. You can then look at the output tables for your baseboard and find out what water temp you will need.
>
> I don't have first hand experience with the Burnham mod con. I do like the design of the Firetube K2 over the Alpine.

What about the firetube do you like? I will be going with the xc series, which I believe is based on watertube.

Zman

The water tube is basically a coil of small diameter tubing. It requires a much larger circulator than the firetube. This increases energy consumption.
A system like yours would require an additional circulator with a water tube which would likely be un necessary with the firetube.

The design of the firetube also allows.it to self clean. They generally need less maintainance.

NY_Rob

What is the minimum turndown of the Burnham mod-con?

That 50' fintube zone might cause short cycling if the Burnam can't modulate down to a low enough fire rate... especially on warmer days where the ODR lowers the SWT below 120F.

- On a warmer day, with a SWT of 120F, figure an AWT of 110F... using 160BTU/ft of baseboard that 50' zone can only dissipate 8,000BTU's. If you use a high (10:1) turndown mod-con like the HTP UFT-80W you'll just be on the edge of short cycling, but a larger boiler or one with a lower turn down ratio with without a doubt short will short cycle.

Would combining zones work for you? That would solve any short cycling issues even with a larger boiler with less turndown.

Suzook

> @NY_Rob said:
> What is the minimum turndown of the Burnham mod-con?
>
> That 50' fintube zone might cause short cycling if the Burnam can't modulate down to a low enough fire rate... especially on warmer days where the ODR lowers the SWT below 120F.
>
> - On a warmer day, with a SWT of 120F, figure an AWT of 110F... using 160BTU/ft of baseboard that 50' zone can only dissipate 8,000BTU's. If you use a high (10:1) turndown mod-con like the HTP UFT-80W you'll just be on the edge of short cycling, but a larger boiler or one with a lower turn down ratio with without a doubt short will short cycle.
>
> Would combining zones work for you? That would solve any short cycling issues even with a larger boiler with less turndown.

It has a 5:1 turndown. I could consider combining zones, but worried the 2nd floor would wind up being too warm. Another thing to throw in the mix. Boiler and the indirect hw will be in an unheated garage. Anything to worry about with that?

Suzook

> @NY_Rob said:
> What is the minimum turndown of the Burnham mod-con?
>
> That 50' fintube zone might cause short cycling if the Burnam can't modulate down to a low enough fire rate... especially on warmer days where the ODR lowers the SWT below 120F.
>
> - On a warmer day, with a SWT of 120F, figure an AWT of 110F... using 160BTU/ft of baseboard that 50' zone can only dissipate 8,000BTU's. If you use a high (10:1) turndown mod-con like the HTP UFT-80W you'll just be on the edge of short cycling, but a larger boiler or one with a lower turn down ratio with without a doubt short will short cycle.
>
> Would combining zones work for you? That would solve any short cycling issues even with a larger boiler with less turndown.

Combing zones is doable, but I'm worried it would be too warm on 2nd floor. The Burnham has 5:1 turndown. Another thing to mention is boiler will be in an unheated garage. Not sure that matters?

NY_Rob

A 5:1 turndown isn't much.... what's it's BTU output?

The boiler placement in an unheated garage isn't significant (unless it goes below freezing in the garage).

Suzook

> @NY_Rob said:
> A 5:1 turndown isn't much.... what's it's BTU output?
>
> The boiler placement in an unheated garage isn't significant (unless it goes below freezing in the garage).

80k unit, garage has gotten below freezing, but I will enclose it in its own space, and insulate.

NY_Rob

An 80K BTU boiler with a 5:1 turndown modulates down to 16K BTU's. In order to not short cycle on calls from the 50ft zone- your SWT (Supply Water Temp) will have to be a minimum of 140F or above... and you'd never condense at that SWT.

You need to use a smaller boiler with a lower output or one that can modulate down lower, or combine zones to make one large zone. If you combine zones and are worried about overheating the upstairs zone- you can use a globe valve to throttle the upstairs zone a bit if needed.

Suzook

> @NY_Rob said:
> An 80K BTU boiler with a 5:1 turndown modulates down to 16K BTU's. In order to not short cycle on calls from the 50ft zone- your SWT (Supply Water Temp) will have to be a minimum of 140F or above... and you'd never condense at that SWT.
>
> You need to use a smaller boiler with a lower output or one that can modulate down lower, or combine zones to make one large zone. If you combine zones and are worried about overheating the upstairs zone- you can use a globe valve to throttle the upstairs zone a bit if needed.

The net ahri is 64k...Not sure that matters? I'm thinking maybe I should just go with the ci boiler.

gschallert

Suzook said:

Combing zones is doable, but I'm worried it would be too warm on 2nd floor. The Burnham has 5:1 turndown.

If it were me I'd convert to one zone but even if you didn't there are ways to mitigate short cycling on the smaller zone during the shoulder seasons. I've noticed that many modcons have some sort of built in anti-short cycling setting, you can use t-stats to control cycles per hour per zone and also use the ODR curve itself.

As far as overheating the upstairs zone if you were to combine them you can always close some of the convector vents. I have to do this with a second floor family room that has 50% more slantfin than the room needs so half of them are closed the whole season. Sometimes simple solutions can be quite effective. :-)

Suzook

> @gschallert said:
> Combing zones is doable, but I'm worried it would be too warm on 2nd floor. The Burnham has 5:1 turndown.
>
> If it were me I'd convert to one zone but even if you didn't there are ways to mitigate short cycling on the smaller zone during the shoulder seasons. I've noticed that many modcons have some sort of built in anti-short cycling setting, you can use t-stats to control cycles per hour per zone and also use the ODR curve itself.
>
> As far as overheating the upstairs zone if you were to combine them you can always close some of the convector vents. I have to do this with a second floor family room that has 50% more slantfin than the room needs so half of them are closed the whole season. Sometimes simple solutions can be quite effective. :-)

Ok, worst case scenario, unit short cycles....It's still running at 88%...Still better than the ci. And it's actually cheaper.

ChrisJ

The modcon requires more maintenance and is both more likely to fail and more costly to repair.

The modcon may not save you anything over ol' reliable in the long run. Will the modcon make it 25-30 years?

In my opinion the only thing the modcon has to offer is greater comfort. The savings is questionable if even existent. Greater comfort is something to consider, but is it what you're after?

There are many opinions out there, consider them all.

gschallert

Suzook said:

80k unit, garage has gotten below freezing, but I will enclose it in its own space, and insulate.

I wouldn't put any boiler in any unheated space that has reached or could reach freezing temp, but that's just me. I'm sure other people do and/or use glycol. Even with freeze protection built in with a modcon you have condensate to keep from freezing. Is your indirect DHW tank going to be in the same location? If you're building a mechanical room in an unheated garage that has gotten below freezing you might want to add some freeze protection into the room design and think about bumping up the insulation on your hot water tank.

Suzook

> @ChrisJ said:
> The modcon requires more maintenance and is both more likely to fail and more costly to repair.
>
> The modcon may not save you anything over ol' reliable in the long run. Will the modcon make it 25-30 years?
>
> In my opinion the only thing the modcon has to offer is greater comfort. The savings is questionable if even existent. Greater comfort is something to consider, but is it what you're after?
>
> There are many opinions out there, consider them all.

Comfort is fine. Just looking to finally get rid of my oil boiler and hw heater. Both are in my laundry room. I guess I will just go with the ci. It's a proven boiler, along with working as it is intended with my current situation.

Suzook

> @gschallert said:
> 80k unit, garage has gotten below freezing, but I will enclose it in its own space, and insulate.
>
> I wouldn't put any boiler in any unheated space that has reached or could reach freezing temp, but that's just me. I'm sure other people do and/or use glycol. Even with freeze protection built in with a modcon you have condensate to keep from freezing. Is your indirect DHW tank going to be in the same location? If you're building a mechanical room in an unheated garage that has gotten below freezing you might want to add some freeze protection into the room design and think about bumping up the insulation on your hot water tank.

Yes, indirect will be in same in heated garage. My plan is enclose it, and insulate. My other thought is a section of fin inside the room to keep it at least on the warm side.

NY_Rob

Suzook said:

... Ok, worst case scenario, unit short cycles....It's still running at 88%...Still better than the ci. And it's actually cheaper.

It's generally accepted that short cycling is one of the worst things you can do to a mod-con and will possibly lead to an early death of the unit.

If you can't/won't use a mod-con with a higher turndown (HTP UFT-80W) that will accommodate your short 50' zone without short cycling- then for the 3% loss of efficiency vs. a mod-con, you're probably better off going with a CI boiler that has some thermal mass to prevent short cycling and it will outlive an abused mod-con.

FWIW- You could use a buffer tank with a 5:1 turndown mod-con, that would solve your 50' zone short cycling problem... but it would $$ to the project cost.

Brewbeer

If the unit short cycles, it will be less efficient than published values.

gschallert

ChrisJ said:

The modcon requires more maintenance and is both more likely to fail and more costly to repair.

A generalization that I don't agree with. My CI boiler got inspected and cleaned annually with any necessary repairs made before heating season. Venting/exhaust inspected and cleaned, burners taken out and cleaned, combustion tested and tuned, etc. This was a regular fall maintenance cost upwards of $200 not counting any parts needing replacement. The same annual cleaning and safety checks need to happen with modcons. My heating company charges the same labor rate regardless of equipment.

ChrisJ said:

The modcon may not save you anything over ol' reliable in the long run. Will the modcon make it 25-30 years?

You're making an assumption that today's CI boilers are the workhorses that yesterday's CI boilers were. I've got my fingers crossed I get the 15 or 20 years I need out of the one I just installed but it wouldn't surprise me if I didn't. Things aren't made to last anymore, for a variety of reasons.

ChrisJ said:

In my opinion the only thing the modcon has to offer is greater comfort. The savings is questionable if even existent.

I would love to get the monthly fuel savings my in-laws are getting with their Vitodens 100, even allocating for different fuels and slightly lower heat loss I estimated I could save 35%+ or more if I had gone with a modcon instead of cast iron. I'll get that fuel savings next season but only because I spent another few grand to install a mini-split with heat pump for the shoulder seasons and supplemental to CH on design days. Suzook's upfront cost after rebates puts the modcon at a lower price point than the CI, combined with annual fuel savings that's hard to beat when CI's no longer have the reputation of lasting several decades before needing replacement.

ChrisJ

@gschallert You'll find few people do that with cast iron boilers, yes, even modern ones. Most get neglected until there's a problem and even then it's easily repairable.

Neglect a modcon and see what happens.

I'm curious, why do you think you won't get 15 years out of a cast iron hot water boiler?

Ah, the magical "30-40% savings" number pops up again.
Spend the money on tightening your envelope and insulation, you'll save more that way.

Of course, that's just my opinion. Doesn't mean I'm right.

JUGHNE

Will you need to elevate the ignition source/burners 18" above the garage floor? If enclosed then outside combustion air needed for CI?

ChrisJ

JUGHNE said:

Will you need to elevate the ignition source/burners 18" above the garage floor? If enclosed then outside combustion air needed for CI?

@JUGHNE brings up a good point, combustion air.
I also missed that you said a power vented CI boiler.

With those things on the plate, I think you should go modcon.

gschallert

@Suzook, the example given in this article by Dana Dorsett is fantastic for explaining modcon efficiency and short cycling and teaches you how to analyze for yourself what equipment is best suited for a particular scenario. It's what I used to ensure that my in-laws 37k low fire modcon wouldn't short cycle. 16k wouldn't even give me a moments pause in your case.

http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/sizing-modulating-condensing-boiler

@ChrisJ, research. I spent six months researching cast iron boiler replacements. Looking at warranties (which can be used in a general sense for how much confidence companies have in their products longevity), failure rates, manufacturing changes from quality of materials (castings) to manufacturing origin. I picked the best of the worst and hope that my adherence to service and monitoring of water quality issues gets me at least past the 10 mark. Had I not planned on installing a mini-split this year I would have gone with a modcon myself. IMO, the only justifiable reason for going with CI over modulating or modcon is price. When CI was significantly lower in cost it definitely made sense if cost was a major factor in the decision. With prices dropping drastically, factoring in energy rebates and enticing warranties on many modcons you have to come up with a compelling technical reason to stay with older technology that may have the reassuring comfort of name but not the same quality of manufacture.

My own opinion is that the HVAC industry is moving toward a strategy of planned obsolescence and that might be a good thing. With us being on a precipice of energy resource transformation maybe it's smart to have 10 year lifespans built into the technology.

Suzook

> @JUGHNE said:
> Will you need to elevate the ignition source/burners 18" above the garage floor? If enclosed then outside combustion air needed for CI?

Yes, I will. Not a big deal though.> @ChrisJ said:
> Will you need to elevate the ignition source/burners 18" above the garage floor? If enclosed then outside combustion air needed for CI?
>
> @JUGHNE brings up a good point, combustion air.
> I also missed that you said a power vented CI boiler.
>
> With those things on the plate, I think you should go modcon.

Also not a big deal, as I will intake from the out side wall of the enclosed room, along with a vent to the attic above. My fresh air at that point is easily taken care of. I am still amazed at the love hate of a modcon these days. In this day and age, we should be beyond this. No?

gschallert

ChrisJ said:

Ah, the magical "30-40% savings" number pops up again.

It's not "magical" when I've run the numbers. ;-)

ChrisJ said:

Spend the money on tightening your envelope and insulation, you'll save more that way.

Already done. Nothing more to be gained.

ChrisJ

gschallert said:

ChrisJ said:

Ah, the magical "30-40% savings" number pops up again.

It's not "magical" when I've run the numbers. ;-)

ChrisJ said:

Spend the money on tightening your envelope and insulation, you'll save more that way.

Already done. Nothing more to be gained.

If a cast iron boiler is say, 85% efficient, how can you save 35% over that?


@Suzook There's a reason for the love hate modcons have.

Suzook

Even more confused than ever....Keep the comments coming. BTW, I am a handy guy, that will do most of the yearly maintenance myself.

JUGHNE

So if CI you can raise the boiler 18" on a non combustible surface? You may not want combustion air from the garage or maybe even the attic.....thinking of chemicals from either source.

Love/hate on ModCon's....great when working......bad when out of warranty and repair parts are several hundred dollars.

As far as early change out in the future for increased efficiency, we already have claims into the high 90's for AFUE numbers.
Do we trash existing equipment to gain another 1.5% or so.
But I digress.

For your situation I would advise the ModCon....wall mount or on a shelf for the 18". Outside air for combustion for clean air. IMO

gschallert

ChrisJ said:

If a cast iron boiler is say, 85% efficient, how can you save 35% over that?

No emoji so I'm not sure if you're kidding or not... in case you are actually asking how a modulating boiler can save fuel costs (which is what my 35%+ referenced) over a non-modulating boiler refer to the modulating aspect. Condensing efficiency rating is not the same as modulating efficiency. Heck I'd pick a non-condensing modulating boiler over a non-modulating CI.

ChrisJ

gschallert said:

ChrisJ said:

If a cast iron boiler is say, 85% efficient, how can you save 35% over that?

No emoji so I'm not sure if you're kidding or not... in case you are actually asking how a modulating boiler can save fuel costs (which is what my 35%+ referenced) over a non-modulating boiler refer to the modulating aspect. Condensing efficiency rating is not the same as modulating efficiency. Heck I'd pick a non-condensing modulating boiler over a non-modulating CI.

No, wasn't kidding.
I don't see how a modcon will save 35% over a non-modulating CI boiler. 5% to 10% ok, but 35%?

I realize cycling hurts efficiency some, but it's not hurting it that much.

gschallert

ChrisJ said:

No, wasn't kidding.
I don't see how a modcon will save 35% over a non-modulating CI boiler. 5% to 10% ok, but 35%?

I realize cycling hurts efficiency some, but it's not hurting it that much.

Okay...maybe you're confused because I used %. My 35%+ fuel savings is not efficiency or AFUE, it's out of pocket monthly fuel savings based on lower BTU consumption due to the fact that modulating burners can modulate down to the heat load but non-modulating CI's are on/off.

A large percentage of the customers who convert from CI to modcon see 30%-40% annual fuel savings not from the condensing aspect but the modulation of the firing rate.

ETA: here's a simpler way to think of it, boiler efficiency % be it 95% or 85% is the utilization of the dollar you've already sunk into heating your home. Condensing efficiency or AFUE efficiency can only give you that narrow 85 - 95 window which is why basing cost savings on that is rather insane, it's fairly small even in aggregate over the course of a year. I see a lot of consumers mistakenly use that figure in cost analysis and completely overlook the modulation savings. Modulation reduces the dollars you spend heating before you even get to the utilization aspect.

Suzook

Burnham has a zone control that adjusts the firing rate to compensate for small zones that won't condense properly. Thoughts?