Need help deciding on a new boiler

[Charlie123]

Hello, hoping you professionals can help me to narrow down my choice on a new boiler for my ~30 year old, 918 sq ft house on Long Island.

I currently have a Utica OBT-3, and while it still works, and I have a service contract with Petro Oil, I think it might be time to consider replacing. The main motivator is the fact that even in summer, the boiler room is always warm due only to the fact that it's maintaining hot water.
I'm maintaining 50 gallons of hot water for 2 people, and the boiler guys I've met don't think it makes sense to just replace the water heater, and I agree.

A Biasi boiler with Riello burner seems to be a frequent recommendation, the 3-pass design and efficiency being the selling points. I'm told that due to the depth requirements of the Biasi, we might want to orient it sideways and then exhaust out at what I assume would be a 90 degree angle.
Is this ok, or are we losing something in that right angle exhaust?

I'm pretty sure that the Riello burner is what I want, no one seems to dispute that they're very good, but I'm trying to narrow down the boiler to the Biasi, Peerless, or Trio, which is supposed to be similar to Biasi but might be shallower.
I also have to consider the possibility that I might need to put a sleeve into the chimney, which I believe the Peerless will not require.

Other info: Taco panel, circulators, Vaughn 35 water tank.

Can you guys help me to narrow down my boiler choices?
Thanks for any info you can provide.

 

[Dana]

First run a fuel-use based load calculation on WINTER fill ups only (not fillups after April 1st, not prior to January first.) If you're on a regualar fill-up service that stamps a "K-factor" on the slips, that's enough information to go on. The 99% outside design temp for virtually all L.I. locations is 15F, so use that as the design temp (yes, I know it gets colder than that, for only 1% of all hours over an average year- the load at the 99% percentile it enough information to size the boiler correctly.)

Then measure up the radiation, zone by zone and add it up for the whole house.

If the Utica OBT-3's idling temperature can be brought down to 140F and still heat the house at the high-limit setting that's the first place to start. If there are only dumb aquastat controls on the boiler it may be worth investing in a retrofit heat purging boiler controller, but let's run the other analysis first.

For the record, which version of the OBT-3 do you have? They are decent triple pass boilers with high efficiency but even the smallest is a 4-plate beast with a DOE output of 105,000 BTU/hr, which is enough boiler to heat my antique 2x4 framed 2400' bungalow + 1600' of insulated basement at an outdoor temperature of -175F (a temperature probably not seen on Long Island even during the last ice age.) The non-EnergyStar version of the 4-plate TRB4095 is DOE rated at 133,000 BTU/hr, but could be safely retrofitted with the same nozzle used on the 105K-out TRB4075 (the Energy Star labeled version, which may have a few other differences, such as an automatic flue damper, etc.)

With the exact model number and the fuel-use based load number along with the radiation sizing we can estimate your oversize factor, and with your radiation we can estimate the minimum water temperature needed to deliver the heat during cold weather, all of which bear directly on whether it's better to replace the boiler rather than reconfigure the system to operate at a higher efficiency/lower standby loss.

A typical ~1000' house over 1000' of uninsulated basement would have a design heat load of less than 15,000 BTU/hr, so it's highly likely that even at 105K output your oversize factor is in the "ludicrous" 7x+ range. Even the smallest oil boilers out there will be at least "ridiculous" range, but it may be OK with heat purging boiler controls and sufficient radiation.

If after looking at the numbers look like that isn't in the cards, a house that size could be reasonably heated with cold-climate heat pumps at lower operating cost (even at L.I. electricity prices) than a ridiculously oversized oil boiler, and that could very well be the "right" way to spend the mechanical equipment budget.

 

[Sponsor]

 

[Dana]

Was that too much information?

In all seriousness, for a "...~30 year old, 918 sq ft house on Long Island..." I'd strongly consider a 3/4 ton or 1-ton cold climate mini-split heat pump, and mothballing the beastie-boiler system as the "Hail Mary" backup system should the mini-split ever fail, or the next ice age shows up and it hits -50F or something.

Any new boiler would require a stainless flue liner properly sized for the boiler, and there is no such thing as an oil boiler truly properly sized for your heat load (unless you sleep with the windows open on the coldest nights of the year! )

A 3/4 ton Fujitsu -9RLS3 can deliver 15,000 BTU/hr @ +5F, and it's unlikely that your heat load at +5F is any higher than that (unless you have the crummiest late-80s house on Long Island.) The installed cost in my area (MA) would be less than $4K, all-in. The 1-ton Mitsubishi FH12NA is good for about 16,000 BTU/hr @ +5F and still under $5K. A 1.5 ton ducted Fujistu 18RLFCD is good for over 20,000 BTU/hr. The installed cost depends on the complexity of the duct work, but it still wouldn't much more than a brand new oil boiler. Any of those will modulate with load down to an output of less than 4000 BTU/hr, delivering very stable room temperatures and high comfort. With fuel-use derived heat load numbers we could come up with the most appropriate solutions. They all deliver very high efficiency cooling too.

A standard electric water heater would be pretty cheap, but a heat pump water heater in the basement would keep the basement air drier, turning basement dampness into heat stored in the tank and condensed water to dispose of down a drain.

 

[Charlie123]

Was that too much information?

In all seriousness, for a "...~30 year old, 918 sq ft house on Long Island..." I'd strongly consider a 3/4 ton or 1-ton cold climate mini-split heat pump, and mothballing the beastie-boiler system as the "Hail Mary" backup system should the mini-split ever fail, or the next ice age shows up and it hits -50F or something.

Any new boiler would require a stainless flue liner properly sized for the boiler, and there is no such thing as an oil boiler truly properly sized for your heat load (unless you sleep with the windows open on the coldest nights of the year! )

A 3/4 ton Fujitsu -9RLS3 can deliver 15,000 BTU/hr @ +5F, and it's unlikely that your heat load at +5F is any higher than that (unless you have the crummiest late-80s house on Long Island.) The installed cost in my area (MA) would be less than $4K, all-in. The 1-ton Mitsubishi FH12NA is good for about 16,000 BTU/hr @ +5F and still under $5K. A 1.5 ton ducted Fujistu 18RLFCD is good for over 20,000 BTU/hr. The installed cost depends on the complexity of the duct work, but it still wouldn't much more than a brand new oil boiler. Any of those will modulate with load down to an output of less than 4000 BTU/hr, delivering very stable room temperatures and high comfort. With fuel-use derived heat load numbers we could come up with the most appropriate solutions. They all deliver very high efficiency cooling too.

A standard electric water heater would be pretty cheap, but a heat pump water heater in the basement would keep the basement air drier, turning basement dampness into heat stored in the tank and condensed water to dispose of down a drain.

 

[Charlie123]

Was that too much information?

In all seriousness, for a "...~30 year old, 918 sq ft house on Long Island..." I'd strongly consider a 3/4 ton or 1-ton cold climate mini-split heat pump, and mothballing the beastie-boiler system as the "Hail Mary" backup system should the mini-split ever fail, or the next ice age shows up and it hits -50F or something.

Any new boiler would require a stainless flue liner properly sized for the boiler, and there is no such thing as an oil boiler truly properly sized for your heat load (unless you sleep with the windows open on the coldest nights of the year! )

A 3/4 ton Fujitsu -9RLS3 can deliver 15,000 BTU/hr @ +5F, and it's unlikely that your heat load at +5F is any higher than that (unless you have the crummiest late-80s house on Long Island.) The installed cost in my area (MA) would be less than $4K, all-in. The 1-ton Mitsubishi FH12NA is good for about 16,000 BTU/hr @ +5F and still under $5K. A 1.5 ton ducted Fujistu 18RLFCD is good for over 20,000 BTU/hr. The installed cost depends on the complexity of the duct work, but it still wouldn't much more than a brand new oil boiler. Any of those will modulate with load down to an output of less than 4000 BTU/hr, delivering very stable room temperatures and high comfort. With fuel-use derived heat load numbers we could come up with the most appropriate solutions. They all deliver very high efficiency cooling too.

A standard electric water heater would be pretty cheap, but a heat pump water heater in the basement would keep the basement air drier, turning basement dampness into heat stored in the tank and condensed water to dispose of down a drain.

Hi Dana,
Sorry, I only realized that someone here had taken the time to reply.
Apparently, my heat loss is less than 25k btu/hr.
My original choices above later turned into: Trio (or Biasi), Buderus, EK, or an LP mod-con system.
It seems that, based on the added cost of the latter 2 systems, the increased efficiency would't be worth it.
Do you have any thoughts on Buderus vs Biasi/Trio? Maybe because they're pretty top-end, I'm seeing criticisms of Buderus, where I don't really see criticisms of the Bisai and Trio.

Regarding the systems you mentioned, I'm thinking that these run on electricity?
I haven't spent too much time on them, but I see the large on-wall component and then what appears to be a fan: does the large unit go in the main room, or wherever you want it, and the other piece functions as a space heater? Do you control these via an app that operates them as a system?

I'm wondering if these units would have been a great idea when they were building the house, but it might make less sense now. I'm also not sure I have the wall space for the units. And I'm guessing that my baseboard heating will just stay there, unused?

I'll look a but further into this, but depending on what combination of units I need, that expense, plus the cost of electricity, might rule these out for me.
Thanks for the suggestion.

 

[Dana]

The triple pass Biasi has a pretty good reputation as a good value for the price. I don't know much about the Trio. Buderus has a good reputation on quality, but they're usually more expensive. The Burnham MPO-IQ oil boilers also have a decent reputation.

Any oil boiler that you install should be the absolute smallest in the series and come fitted with a heat purging boiler control. Any new boiler would require a right-sized stainless flue liner for the BTU input of the burner, or the acidic flue condensation will destroya terra-cotta lined chimney in under a decade, especially if the terra cotta liner is oversized (= lower stack velocity, more surface area, more exhaust condensation.)

The amount of radiation also affects how the system is configured. In the unlikely event that you have enough radiation that the return water entering the boiler would be chronically under 140F it may require some near-boiler plumbing tweaks to mix boiler output with the return water to raise the entering water temp at the boiler. In a house your size it's far more likely that there isn't enough radiation to keep the boiler from cycling on/off during continuous calls for heat from the thermostat. A heat purging boiler control would reduce the amount of cycling and improve overall efficiency, but even the smallest oil boilers out there are going to be ~3x or more oversized for your load. (The Biasi B10/3 puts out 61,000 BTU/hr.)

Yes, mini-split heat pumps run on electricity. Electricity is expensive on L.I. and heating with electric baseboards would be crazy-expensive, but a heat pump pulls most of it's heat from the outdoor air. the efficiency & output capacity varies with the outdoor temperature, and not all mini-splits will cut it, but many will, now that vapor-injection scroll compressors are becoming more common. In your climate a better-class mini-split will use less than 1/3 the amount of electricity to heat the place than heating with electric baseboards. In my area (Massachusetts) Mitsubishi owns the lion's share of the cold-climate mini-split market and there is good support, many installers, but Fujitsu is also widely supported, and has products of comparable or better efficiency. (All others add up to less than 1/3 of the total market in my area.)

It's possible to get mini-splits with ductless floor mounted coils or ceiling units rather than the more common high-mount wall unit. If the floor plan has a larger open space and you're trying to do most of the heating with just one ductless minisplit it's best to install it in the main area set up to blow primarily toward the hall or doors to the other rooms.

^^typical floor console mini-split^^^




It's also possible to use a slim-ducted mini-split mounted in the basement or some out of the way location in the upstairs (but NOT in the attic, above the insulation). For your climate the only ducted units I'd recommend are the Fujitsu -xxRLFCD series. They are more efficient and have more heating capacity at low temp than their competition, as well as a more powerful blower. These aren't like typical hot air furnaces- the blower isn't nearly as powerful as a typical central-air or hot air furnace, and minimizing duct length matters. The blower runs at a lower cubic feet per minute than old-school furnaces and modulates it's speed & output up/down with load very quietly. A single mini-duct cassette can serve 4-5 rooms fairly easily.

The Fujitsu mini-ducted units can also be mounted vertically (unlike the competition), which gives some options. This 1.5 tonner is cooling a heating a ~1200' house in California, with 4 flex ducts coming out of a short plenum, and a common return in the hall, taking up about 7 square feet of floor area:

^^^Note that they ran the ducts below the ceiling level in soffits, to avoid running them in a hot in summer/cold in winter attic. If you have a full basement or deep crawlspace, running the ducts in the basement to floor registers is easier. The grille is just the common return plenum. The mini-duct cassette is the first rectangle/box above it with all of the refrigerant & condensate drain plumbing coming out the side.

There are a series of blog articles on mini-splits on the GBA site, many of which are behind a paywall, but with a free trial subscription you can view them all (for a week or so.)

 

[Charlie123]

Thanks for all the info Dana.
My reference to baseboard was just that my current hot-water baseboard would be rendered unused and unsightly. It can be removed but then we're talking patching/painting.
I will have someone in who works with these systems and see what he says, but the thought of simply replacing what I've already got here appeals to me.
Do these units feed through to the outside, wherever they're installed?
I guess they're basically a forced-air system?
And do they also provide AC in summer?

Should i stay with oil, I'll bring up your suggestion of a heat-purging boiler control.

Thanks again.

 

[Dana]

Mini-splits like other heat pump systems both heat & cool. The distinction is that they are smaller, and modulate the output levels to keep the room at a constant temp rather than cycle on/off. They are also more efficient than traditional large ducted heat pumps. Mini-splits do not have resistance heaters built in as "backup" the way traditional forced hot air heat pumps do, but due to superior compressor technology the better mini-splits don't fall off in capacity or efficiency at low outdoor temps the way old-school heat pumps do, and don't need the auxiliary backup heat.

Mini-split heat pumps have refrigerant plumbing & control wiring between the indoor & outdoor units. They do not introduce ventilation air- the only connection to the outdoors are the refrigerant lines & control/power cabling, which should be air-sealed. The wall-coil & floor console mini-splits are "forced air" only in the sense that they draw air from one end of the indoor unit and blow it out the other end, but the mini-duct versions are a bit more akin to a traditional ducted forced air, operated at much lower air volumes- they're really quiet, and don't have much "wind chill " effect.

When sized correctly mini-splits run nearly 100% of the time during the heating season, adjusting the output as needed to keep the room at a stable temperature as the outdoor temperatures rise & fall over the course of the day/week/ season. When cruising along at minimum speed the efficiency is phenomenally high, but when running full blast or when cycling on/off it takes a bit of an efficiency hit.

How many total feet of baseboard do you have? That is an important factor in sizing the replacement oil boiler, and which control strategies are more efficient.

 

[Charlie123]

Hi Dana, sorry to leave you hanging, figured I'd measure and get back to you, but I think I'm going to go with Buderus or EK, although not sure I'll bite the bullet now.
Thanks very much for your advice, and the education.

 

[Dana]

Hi Dana, sorry to leave you hanging, figured I'd measure and get back to you, but I think I'm going to go with Buderus or EK, although not sure I'll bite the bullet now.
Thanks very much for your advice, and the education.

Still measure up the radiation, and run the heat load numbers- don't assume the installers are going to get it right. If the radiation can't emit at least 75% of the burner's output rate (maybe it can, maybe not) and the heat load is less than 2/3 of the boiler output (almost certainly the case) it will need a heat purging control scheme to hit anywhere near it's nameplate AFUE numbers. The EK System 2000 comes with a well evolved heat purge system, but I believe the Buderus Logamatic 2017 optional smarter control may provide that function. (I haven't really studied the manual on that, but you should.)

Buderus G115WS/3 a direct-vented version with a 0.60 gph nozzle that has a ~75K (DOE) output that is side-vented, which would allow you to brick up the ports in the chimney, lowering the overall heat load of the house. That's probably more than 3x oversized for your actual heat load, but the chimney vented G115WS/3 is even bigger at 0.70 gph. It may be cheaper to side vent it than install a right-sized stainless liner to the existing chimney, or not, but it shouldn't be dramatically more expensive. The direct vent version the better choice here, if there's a reasonable location for the side venting.

The smallest EK1 comes with a 0.68 gph burner, probably something like 4x oversized for your load, but coupled with an indirect water heater it should still come close to it's nameplate AFUE.

 

[Charlie123]

I'll make sure this is taken into consideration.
We did come up with the gallons used per year, although my 550 differs from the 650 that Petro told me today.
Their record keeping isn't great, but if we settle on 600, does this tell you anything?
I was also told that my heat loss was less than 25000 btu/hr, and as far as I know, this was based on my estimate of 535 gals per year.

 

[Charlie123]

Ok, I measured upstairs (I can do the basement as well, although I really don't use it): ~67 feet

 

[Dana]

At an entering water temperature (EWT) of 180F and an average water temperature (AWT) of 170F (180F out, 170F return) a zone with 67' of typical baseboard emits about 33-35,000 BTU/hr. That's less than half the output of the smallest Buderus. Even if you cranked the temperature to an AWT of 200F the baseboard would only be emitting ~50K. Heat purge control will be essential to limiting the number of burn cycles and overall efficiency. At 3x oversizing for the design heat load, without heat purge (even if the boiler were NOT also 2-3x oversized for the radiation) most boilers would average ~5-10% below their nameplate efficiency.

Compare the "Steady State Thermal Efficiency" and "Annual Efficiency1 (%) Oversize = 3" columns in Table 3 of this Brookhaven National Laboratory study. (Note the performance of System #3, which was an EK System 2000, the only one tested that had purge control.)

With short-cycling on insufficient radiation it'll knock another 5-10% off, but those effects would also be blunted by a heat purge control strategy. Do NOT confuse purge control with outdoor reset. Outdoor reset raises and lowers the operating temperature in response to outdoor temperatures. At lower temperature the radiation emits even less, making the oversize factor of the boiler to radiation even higher. Setting the high-limit to the high side, but setting up the heat purge to 140F allows the system to better ultilize the available thermal mass in the system, limiting the number of burn cycles, with longer burns, but also lower standby loss, since the average temperature of the system at idle is lower.

For a few hundred dollars heat purge controls could be retrofitted onto the existing boiler, but without an indirect water heater the idling temperature of the boiler might have to be higher than 140F to deliver reasonable domestic hot water service. Another strategy would be to abandon the tankless coil and used heat pump electric water heater located in the boiler room. That way the low-limit temp of the boiler can be turned down (or off for the summer), and the heat pump water heater would dehumidify the basement in summer, and harvest the standby losses of the boiler during the heating season.