I am considering to do an oil conversion to gas, on my heating system.
The system is a hot water baseboard.
The plumber is recommending a Burnham Boiler, one of the 2 following models, the Alpine, which is a "Gas, Condensing, Stainless Steel Heat Exchanger".
The other model is Series 2, which is a "Gas, Water, Cast Iron Heat Exchanger.
My understanding is that the condensing boiler is NOT designed for a baseboard system. Is it so?
I came across a 3rd model on Burnham web site, the SCG & PVG.
Any recommendations, as to which boiler to use?
I called Burnham, but they will NOT answer any question. They directed me to the plumber who will perform the job. Unfortunately, each plumber has his own agenda, and will answer my question accordingly.
My other question is, on a 2 zone system, should I use a circulating pump for each zone, or one pump with zone valves?
Thanks for any input.
You can definitely run fin-tube baseboard with the condensing Alpine and reap significant fuel savings, just not as much as you'd get with radiation specifically designed for low temps. You'll almost certainly hit the low-90s or higher for an average if the system designer has any competence.
Let's say your fin-tube baseboard was originally designed to deliver sufficient heat to keep up with a peak heat load that occurs at 0F outdoor temps, with 180F water out of the boiler, with 145F water returning from the baseboards. Under those conditions a Series-2 cast-iron beastie is delivering ~81-82% efficiency, but the Alpine would be delivering 86-87%.
But most of the time it's way above 0F, and most of the fuel is burned with heat loads of half your peak. The fin-tube can deliver the half-peak load with 140F outgoing water, with ~118F water returning. Under those conditions you'd have to boost the temp on the cast-iron beast to protect it from destructive condensation, and it would be hitting around 80%- maybe less with cycling losses, whereas with the Alpine using it's "outdoor reset" function you could dial the temps back and you'd be hitting 92% or so. During the even low loads of October or April the series 2 would be gagging at 75% average efficiency, and the Alpine could be hitting the mid-90s. As a practical limit fin-tube begins to be less predicable at average water temps below 120F, so you'll probably be "stuck" at mid-90s efficiency under very low loads where you could be hitting high-90s with different radiation, but that's compared to sub-80 under the same conditions with a cast-iron boiler. (If your baseboards are cast-iron, not fin-tube, you can go much lower and still get predicable results out of an outdoor-reset curve.)
The SCG/PVGs do a bit better- you'd hit mid-80s for an annual average with those, as long as they're sized correctly for the peak heat load.
Sizing is VERY IMPORTANT for any boiler, but even more so for higher-mass cast-iron. In order to get the size right, you need a real heat-loss calculation (and "lessee, that's 2600 square feet times 30 BTU per square foot is..." is absolutely NOT a heat loss calculation, almost guaranteed to oversize to the point of diminishing efficiency, with the higher upfront cost of a too-large boiler.) Demand a computer generated room-by-room and whole-house heat loss calculation from any contractor you use, and those who offer it up ahead of time move to the head of the line. This weeds out the first 90%. Those that also do a full combustion efficiency test at time of sign-off on the installation as a matter of course are the cherished 1-percenters.
The room-by-room calculation along with the amount of baseboard in each room ultimately determines your peak water temp requirements (which will affect efficiency independent of boiler type, but more so with the Alpine), and the whole-house numbers determine the maximum size of the boiler. If cast iron, and the whole-house number is between sizes, pick the smaller- it will be more efficient. With most houses one can economically reduce the peak heat load 10-15% with air sealing and spot-insulation type measures, if it doesn't quite keep up (or even if it does- most heat loss calcs have generous margins built-in.) Oversizing by more than 15% from the calculation would take a measurable toll on efficiency with cast iron. Oversizing by 100% is common, but means it will under-perform it's AFUE test ratings by quite a bit.
With the Alpine the most relevant number from an efficiency is the minimum-input BTUs, so being oversized by the max-BTU number shouldn't turn your toward a smaller cast-iron boiler. the cast-iron has only one number- the burner doesn't modulate the flame up/down, but the Alpine does. The lower the minimum number is, the better the efficiency you can tweak out of the system, as long as the max number still meets your peak heating load need. eg. Let's say your heat loss calculation comes up with 60KBTU for a peak heat load- the Alpine 80's output would be oversized by 21% if you took it's peak-BTU output number, and the SGC3 would be perfectly sized, but since the Alpine-80 can modulate down to 16K when it's warmer than your max-heat load temps outside it will run longer & more efficient burns than the SGC3 literally 99% of the time.
The pumps vs. zone-valves question has a lot of "depends", and can only be answered by doing a real design, and sometimes the answer is "either". If you have a contractor that offered up the heat-loss calc without prompting you can probably just trust them on the rest of it. If one or both of the zones are pretty small, don't be surprised if the designer recommends putting in a buffer-tank to raise the thermal mass of the system (or just one zone), since that would raise the average efficiency by keeping the boiler from short-cycling while serving that zone.
Don't be surprised if they also recommend you use an "indirect" tank for hot water heating operated as a zone (or sometimes a "reverse indirect" buffer tank when going with cast-iron). This is a valid way to raise your net space heating & hot-water heating efficiency by using the boiler. It usually results in more hot-water heating capacity too, but at the very low end of boiler sizing it might mean bumping up one size.
If you end up going with SCG/PVG series, the SCG + indirect hot water is preferable, since it means you can the safely air-seal the house, including the now-abandoned flue that would otherwise be sucking air out of and into your house 24/365 without risk of backdrafting exhaust from a boiler or hot water heater into your house. (Alpine + indirect= same story. Seal up that efficiency-robbing summertime-humidity inducing flue!)
With a zip code and a good estimate of your annual oil use (in gallons, not dollars) we could probably hit pretty close on what your whole-house heat load is, as a sanity check. Using the boiler to measure heat load only works if you don't supplement with wood-stoves, etc. though. It can be more accurate than a heat-loss calc, because there's no inherent margin added just in case the house is air/heat leakier than estimated- it's a measurement, not an estimate. Age/size/ratings of the oil boiler would also be useful in narrowing that down too.
Odds are pretty good that the Alpine would use 30% less fuel than a right-sized series-2, and 25% less fuel than a right-sized SGC. Whether there's any payback in that depends on how much fuel you anticipate using, but from a comfort point of view the Alpine would still be a win, delivering more even heat while operating, due to the much longer burns. If you intend to live there awhile there's value in that, even if you can't make a case for it in a net-present-value financial analysis of fuel savings. I've yet to meet anyone with a modulating condensing boiler who wishes they'd cheaped out on an atmospheric drafted cast iron boiler like a Series-2, even with fin-tube baseboards instead of radiation.
Check out the ES2
Any boiler installed should consider an OD reset control. The ES2 makes this easy and offers troubleshooting with the IQ control. The nice thing about this boiler is it is cast iron but can receive 110f return water temperature which makes it closer to the savings of an Alpine at less investment, maintenance and less expensive parts down the road.
Outdoor reset and 110F return water doesn't buy you anything if the SCG the radiation can deliver design day heat with <150F water. Being atmospheric drafted it may even use more fuel due to the induced infiltration losses in the house. If your design day heat load is <40KBTU/hr (like my house) even the smallest ES2 it won't even meet it's AFUE numbers (but then, neither would the smallest SCG), whereas the Alpine would most likely still meet or exceed it's (already higher) numbers as long as the min-modulation was less than half the design-condition load.
This all has to be sussed out by a pro. It starts out with a heat loss calc, after which a peak water temp requirement can be determined for the in situ radiation. Only then could a call be made as to whether ODR would buy you more than the induced losses of the atmospheric drafted ES2. (In general I prefer sealed combustion over atmospheric draft, since that allows you to air-seal the house to a tighter, more comfortalbe & efficient level without backdrafting risk. YMMV)
I agree with you to an extent. If the boiler is in a boiler room where combustion air can be brought in without making the home go negative upon boiler operation the impact is minimal. Modulation will save some but not as much as most people think. BTU input per hour is BTU input. It does not make much difference whether it is in 2 cycles per our or 4 cycles per hour. The extra standby loss is very minimal when ODR is used and operating at lower water temperatures.
The savings with a mod/con is in the condensing mode. When we can operate at temperatures less than 126f. When condensing you gain about 9k btu's per hour of operation, not per clock hour. When condensing stops you loose the 9K. The majority of the heating cost savings is determined by the near boiler piping and system efficiency. Improve system efficiency by eliminating or properly handle micro-zones. Proper near boiler piping also plays a huge part in boiler and system efficiency.
Boiler efficiency is not a huge part of fuel savings as the efficiency of the boiler changes by the minute when the boiler is running. As vent temps go up efficiency goes down. Mod/cons take a bigger hit on efficiency than cast iron boilers do.
Let's look at life cycle costs. If we are talking about saving money we cannot only talk about fuel savings. What determines life cycle costs?
1. Cost of the product/installation cost
2. Cost of operation
3. Cost of maintenance
4. Cost of replacement parts
5. Lifespan of the product