Need Oil Burner help or advice

[Skeley]

Hi Folks,

Sorry if I sound like an idiot but this is all new to me but need some advice on where to begin with this problem.

I recently purchased a 3200 sq foot house built in 1994 and located up in the catskills NY, the house is a ranch 1600 sq feet (1 st floor ) over 1600 sq feet basement. There are 3 zones in the house, zone 1 is the entire first floor minus the master bedroom which is zone 2 and of course the basement is zone 3. A week after closing I noticed the boiler ( Burnham 120,000 BTU oil unit) was leaking and called in a plumber/boiler company in which they said the unit needed replacing because the leak was coming from the casting seam and that could not be repaired. Fine the day after election day they come and install the new boiler which is a Biasi B10 series B3 boiler with an Riello 40 F3 burner. They wrap up the job in 2 days all is fine and dandy, I go away for a few days and set the house temp to 50' in all three zones. Upon my return I set all three zones to 72', each circulator comes on as it should, (one pump on each zone on the return to the boiler). The house with an exterior temp of 37' could not get past 61' within 31 hours of running time. The boiler was cycling on and off with water temp at High of 180 off and Low at 140 on again. Long behold I look into the boiler a bit more and seen that the folks installed a 61,000 BTU boiler which was half of what was pulled out. Well after so many conversation on what I need to what I didn't need according to them, I had them return and replace the Biasi B10 series B3 boiler with the Riello 40 F3 burner with now a Biasi B10 series B5 boiler with the Riello 40 F5 burner (now 140,000 BTU's), there is also taco 007 circulator pumps on each zone. Okay new boiler is in, zone were all bled from any air pockets yada yada yada. Fire that puppy up and 24 hours later the house will still not get past 62' and that's now with external temp 27-30'.

The house is well insulated, like I said it was built in 1994, not drafty in anyway, and there was zero changes to the radiators which are all slant fin baseboard, it was just a boiler replacement and disconnect and reconnect the piping. The previous system was Burnaham 120,000 BTU single pass unit, which covered all three zones with one Grundfos 3 speed circulator and zone valves. The house would heat from 50' to 74' in just about 4 hours time.

The pex on the current system does get hot on the feed line and on the return line. Not sure exactly what the return temp is but it does come back hot.

Would anyone have any insight where I might look to see why I'm not getting the heat BTU's extracted properly from the boiler or radiators? Could it be possible that I need maybe a little faster pump on the zones to keep the radiators hotter and closer to the higher temp limit rather then maybe returning a bit colder around the 140 limit? I do know that I can raise the high limit a bit more on the burner control box which I didn't want to do so I haven't yet, but the low side I cannot increase it above the 140 mark. Any help would be great, and Happy New Year.

Mike

 

[Dana]

The fact that the boiler is cycling on/off and actually hitting the 180F high-limit means that the radiation isn't delivering the full 67K of DOE output, which indicates low flow, either from air in the system or partially closed valve. Raising the high-limit won't improve the flow. In rare instances it could be that it's under-pumped, but that would be unlikely.

It's unlikely that your 99% heat load is anywhere near as high as the smaller burner's output, and changing it to a bigger boiler was a mistake. Even if the basement has no wall insulation, if at least half of the wall area is below grade your true heat load at -5F or whatever is likely to be under 50,000 BTU/hr, and a 60-67K output burner would be appropriate. The B-5 is sub-optimally (possibly ridiculously) oversized for the likely load, and will never actually hit it's AFUE numbers.

Since you have a heating history on the place, with a ZIP code (for weather data & 99% design temp purposes) and some wintertime fill-up dates & quantities (or a K-factor stamped on a winter fill-up slip) it's possible to establish an upper bound on the true load.

 

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[Skeley]

Thanks for the reply. There was actually two reasons for the bigger boiler the first one was the installer promised the equivalent size as what was in there in which he didn't deliver which I had paid him for so I had my say with him on that which was a contractual agreement, but the other reason is I will be expanding the house and heating eventually into the garage and most likely a second floor raiser so being the bigger one was there at first and I'd like to have the same size back for these soon to be expansions knowing it's all done and capable of heating at that point.

About the high limit yes 180 is the cutoff at this point and the boiler is cycling to such, I was more along the lines of thinking raising the low limit from the 140 mark to 160 /165 mark so there is a 15' differential, maybe with the current 40' differential I'm losing too many BTU's at the radiators?

I just found my control box instructions which is a Hydrostat 3250-Plus and seen that if the low limit doesn't raise past 140' there is a jumper that has to be removed to allow it to increase past the 140 mark. Perhaps this was installed incase the boiler also makes the homes hot water supply, which in my case it does not. I also agree it can be a flow issue and was thinking about removing the taco's and replacing them with B&G NRF-25 3 speed pumps this way we might have a little more control over the flow and scale it back if it's too quick because I hear some say you don't want water circulation too fast as well.

I appreciate your reply and knowledge and will look into some of those areas as you suggested especially the flow.

Thanks
Mike

 

[Dana]

Thanks for the reply. There was actually two reasons for the bigger boiler the first one was the installer promised the equivalent size as what was in there in which he didn't deliver which I had paid him for so I had my say with him on that which was a contractual agreement, but the other reason is I will be expanding the house and heating eventually into the garage and most likely a second floor raiser so being the bigger one was there at first and I'd like to have the same size back for these soon to be expansions knowing it's all done and capable of heating at that point.

About the high limit yes 180 is the cutoff at this point and the boiler is cycling to such, I was more along the lines of thinking raising the low limit from the 140 mark to 160 /165 mark so there is a 15' differential, maybe with the current 40' differential I'm losing too many BTU's at the radiators?

I just found my control box instructions which is a Hydrostat 3250-Plus and seen that if the low limit doesn't raise past 140' there is a jumper that has to be removed to allow it to increase past the 140 mark. Perhaps this was installed incase the boiler also makes the homes hot water supply, which in my case it does not. I also agree it can be a flow issue and was thinking about removing the taco's and replacing them with B&G NRF-25 3 speed pumps this way we might have a little more control over the flow and scale it back if it's too quick because I hear some say you don't want water circulation too fast as well.

I appreciate your reply and knowledge and will look into some of those areas as you suggested especially the flow.

Thanks
Mike

If you build it tight you would still be well within the output of the B-3 Biasi.

Raising the low limit will only cause it to cycle more rapidly. if you were "...losing too many BTU's at the radiators..." the burner would run continuously. The higher the temperature (say, 180F) the more BTU/hr you get out of the radiation. If it's hitting the high-limit at the boiler it means the radiation isn't losing enough BTUs to the room. If you raise the high-limit it would lengthen the burn times, but now that you (probably) have a ridiculously oversized burner for the radiation, it'll still cycle on/off no matter what.

How much baseboard do you have, broken down by zone? (seriously- measure it and report back).

At 180F out/160F return most residential fin-tube delivers about 500 BTU/hr per running foot. So to balance with the 67,000 BTU/hr DOE output of the B-3 would take 67,000/500 = 135' of baseboard. If only one zone is calling for heat and it only has 50' of baseboard it's guaranteed to cycle pretty rapidly. When the boiler hit's it's high-limit it heat-purges the boiler until the temp drops to the low-limit setting, but there isn't a heluva lot of thermal mass in that boiler it purges pretty quickly, provided the flow is really up to snuff.

Unless the Riello has a bigger jet than is shipped standard with the B-5 it's DOE output is 124,000 BTU/hr which would take about 250' of baseboard balance and run continuously with 180F output, which would be an untypically large amount of baseboard for a 1600' house with a 1600' of below-grade basement.

To get more heat out of the baseboard, raise the high-limit, but leave the low limit at 140F, which will minimize the amount of short-cycling. The max setting for the Hydrostat 3250 is 220F, but try setting it to 200F first. At 200 out/180F return, average temp of 190F you should be getting more than 600 BTU/hr per running foot out of typical fin tube baseboard.

A typical fin-tube output vs. temperature chart can be found here.

It's possible that somebody set up the Hydrostat to operate under "outdoor reset" control without tweaking it in or installing the outdoor sensor(?). But you should read and understand the manual, and verify that it's programmed correctly for your configuration, and if it isn't right, call the installers and give them hell. An outdoor reset control raises and lowers the average water temp of the system in response to the outdoor temperature, but the response curve needs to be adjusted so that the temperature is high enough for the radiation to be able to cover the heat load at all outdoor temperature. Adjusted correctly it would take a long time to recover from an ultra-deep setback, but would be able to keep the house at temperature. If outdoor reset was installed, the installer needed to educate you on how to use it, and how to adjust it.

Typically, reasonably tight 2x6 framed ranches with clear-glass double-panes and full basements typically come in with heat load to floor area ratios of about 12 BTU/hr per square foot of above grade space at an outdoor temp of 0F, to about 15 BTU/ft-hr if the foundation isn't insulated. If the foundation walls are insulated the heat load of a 1600' of basement would be under 10,000 BTU/hr unless it's a pretty air-leaky house. The real heat load is from the fully above-grade space. So in all likelihood your heat load is on the order of (12 x 1600= ) ~20,000 BTU/hr, to (15 x 1600'=) ~25,000 BTU/hr. If it's a walk-out basement with a big glass slider door or two you might be in the 30-35K range @ 0F, but you're nowhere NEAR 67,000 BTU/hr unless you have a more than code-legal amount of window area, no foundation insulation with a large amount of above-grade exposure on the foundation, or some truly MAJOR air leaks.

Even with 35,000 BTU/hr of heat load at the 99% outside design temperature (not likely), at the ASHRAE recommended 1.4x oversizing factor you would only be at 49,000 BTU/hr of boiler output, and the 67,000 BTU/hr output of the B-3 would be 1.9x oversized, which is higher than the presumptive 1.7x oversizing in AFUE testing. Bumping it to the B5's 124,000 BTU/hr output make it 3.5x oversized, and guaranteed to NOT hit it's AFUE numbers, even with the heat-purging controller set to maximum differential.

Only if you had unusually (and ridiculously) large domestic hot water needs would you ever up-size the boiler beyond what is reasonable for the space heating load.

Seriously run a fuel-use based heat load calc base on how much oil the old boiler was using during winter weather. If you have a K-factor stamped on a mid or late winter fill up slip that's enough information to work with (K-factor is defined as heating degree days per gallon of oil), otherwise exact fill-up dates and volumes and a ZIP code to be able to look up the degree day data works. The basic methodology is outlined in this bit o' bloggery.

 

[Skeley]

Wow that's a lot of info and now my head is spinning lol. I have not tried any of those adjustments as of yet but I do know my radiator footage.

Zone 1 -Most of the first floor is 68 feet

Zone 2 -Master bedroom and bathroom is 16 feet

Zone 3 - Basement with bare poured foundation walls is only 30 feet of pipe that goes into a fan/blower unit. (this will change as I finish the basement).

Now when they installed the boiler they cut some copper and ran pex, is the 200' number safe for pex? In addition there was definitely no outdoor reset sensor installed at all, but that doesn't mean the control box isn't in some sort of program mode.

I do have a question about that chart, there is a line the stats:

BTU/HR. per linear ft. with 65°F entering air

Does that mean the BTU ratings are when the air temp in the home is at 65'? I ask because I keep the home at 50' when not there, and remote raise the therms to 72' when I'm on my way to the home, and from the time I increased the temp 31 hours later the house still would not get past 60-61'. I don't know for sure but that time frame seems unreasonable to get to temp. If you tell me 4-6 hours yeah I can see that, who knows maybe I'm wrong.

Another question is about the Low limit, when set at 140 or 160 etc.... and High limit set to 180 or 200 etc... Does the boiler keep firing to maintain that water temp even when the therms are not calling for heat or only when the therms are calling for heat? This boiler is strictly heat and separate from the homes hot water supply tank.

Dana I appreciate all your help and advice, as far as it goes for the setting adjustments I will advise you on that when I get up to the home and make them. I will even bring a heat gun and see the temps on the feeds and returns.

Happy New Year.

Mike

 

[Dana]

In a 70F room the air temp near the floor is typically about 65F, and the air near the ceiling is closer to 75F. It'll put out a lot more when the entering air is 50F. The increased output is about the same as raising the average water temp by 15F in the 70F room. (Say 185F AWT instead of 170F AWT.)

The air coil probably has a BTU rating on it somewhere, but the basement load is pretty tiny compared to the rest, so it won't normally be overlapping calls for heat from the other two zones.

With 68' + 16' of baseboard you're at 84' total. With 67,000 BTU/hr of boiler output of the B-3 that's about 800 BTU/per hour per foot of baseboard. That would balance with an AWT of about 210-215F, so if you cranked the high-limit to 220F it wouldn't cycle much. But for the 124,000 BTU/hr output of the B-5 you're pretty much screwed: 124,000/84'= ~1500 BTU/hr per foot, which means even if you cranked the high limit to 220F it would cycling on/off at a ~50% duty cycle even with both zones calling for heat.

Given that they only installed 84' of baseboard odds are the original system designer presumed a heat load of no more than 600 x 84' = ~50,000 BTU/hr, and even that would typically be 2x reality. Why they installed a 120K Burnham with only 84' of baseboard is a mystery, unless it had an internal coil for the domestic hot water.

The max output you can get out of the boiler is constrained by the limited amount radiation, but at ~40,000 BTU/hr out of the radiation (about what you would get with the boiler set to 180F high temp) you should have no problems bringing the house from 50F to 70F in less than a couple of hours when it's only 35F outside, though it could take awhile at 0F. It's a matter of raising the thermal mass of everything inside the insulation up ~20F. At 35F your heat load is probably no more than 15,000 BTU/hr so you have 25,000 BTU/hr of "extra" to raise the temperature of the materials. But at 0F your load could be ~30K, and you'd only have ~10,000 BTU/hr of extra when approaching the 72F setpoint temp.

Read the manual on the Hydrostat 3250, but I suspect it always maintains 140F if it's set up for a boiler not designed for cold-starting, but might be progammable for cold-start as well. When it hits the low-temp limit it' fires up to some other temperature that it probably calculates from the last call for heat from the thermostats, but won't hit the high-limit unless there is a continuous call for heat. There are several programmable heat purging controllers out there on the market, I've never read the full details on that one.

Most PEX is still good for 200F at normal system pressures, even if the specs on some products only say 180F. Taking it to 220F might be pushing your luck.

If the basement is not insulated, be sure that you DO insulate it prior to finishing. Most of the Catskills falls within US climate zone 6A, where the IRC 2015 code-min for foundation would R15 continous insulation, or 2x6/R19 studwall. The studwall approach is a mold-hazard since it would require an interior side vapor retarder to avoid frost in the above grade section, and the vapor retarder would trap ground moisture in the susceptible studwall.

You can get the necessary thermal performance in a more moisture-resilient manner by installing 3" of polyiso or 4" of EPS strapped to the wall with 1x furring through-screwed to the foundation with masonry screws, or 2" of EPS or 1.5" of polyiso trapped to the foundation by a 2x4/R13 studwall that has no true vapor barrier on the interior side (no poly, no foil, but kraft facers are OK.) The foam acts as a vapor retarder against ground moisture, but keeps the average temperature at the foam/fiberglass boundary above the average dew point of typical wintertime indoor air. It's worth installing an inch of EPS under the bottom plate of the studwall as a capillary & thermal break from the slab, keeping it above the summertime dew point temperatures too, in which case you need not use pressure treated lumber. Used rigid foam in good condition can often be had for less money per R than batts through foam reclaimers such as this outfit in Mayfield NY.