Cracked boiler

[Henbogle]

I just heard from my plumber that the water on the basement floor is from a cracked boiler. I think it is a Burnham oil-fired V-75-1 or V-73-1 (the tag is hard to read). My plumber said that Burnham had a series of flawed boilers in the not-too distant past and this might be one of them and that Burnham might provide some recourse.

Nonetheless, I will need a new boiler, and that is why I am here seeking advice. The home is a 1330 sq. ft. ranch with a partial daylight basement. There is a section of the basement we hope to finish off in the future. The place was built in 1974, and has had 2 additions, a sunroom and a master bath. It has 6" of fiberglass insulation in the walls and attic. We purchased in May, so have no records of the amount of oil needed to heat the home, but we are in cold snowy Maine so we need a good heat source. It is on a single zone.

We have been working on an extensive renovation. Part of the renovations included replacing some of the HW baseboards due to removing a wall and partitioning a room. In those cases we added a Smith toe-kick heater, some Slant-Fin baseboard, and 2 Pensiotti towel-warmer radiators. We also replaced the electric baseboard in the sunroom with a Smith HW convector radiator with a fan. We've also done some air-sealing, and will be insulating and air sealing the basement sills.

I am seeking suggestions for a new boiler. Our plan is to rent the home for a few years and eventually retire there. The main area of the house is very open, but the bedrooms are down a narrow hallway, which makes me think we might consider a heat pump in combination with a boiler? We do get excellent solar gain and had been considering adding solar in the future as we are running out of funds as we approach the end of the renovation. I hope this is enough information to give me some advice! Given this information, I would really appreciate some suggestions. Thanks in advance.

 

[Dana]

Some parts of Maine are much colder that others, so it's tough to hazard what your 99% outdoor design temp might be, which is relevant to whether or not there are heat pump solutions that work. Got a ZIP code?

Is there basement under all rooms, or just one part of the house? Is the foundation insulated (or going to be), rather than just the foundation sills & band joists? If not, they should be, but don't just slap up a fiberglass insulated studwall or you'll be in the mold-farming biz. (The remodel forum on this site has numerous threads on the subject.

The "right" thing to do would be to run a Manual-J heat load calculation on the "after" picture of the house post-renovations, using aggressive assumptions about air-tightness.

Only when you know the size of the heat load can you pick reasonable solutions. The most common error is to oversize the boiler /furnace/ heat-pump, which cuts into both efficiency & comfort, and sometimes cuts into longevity.

Another important factor for boiler selection is the number of zones, and the amount & type of radiation on each zone. Avoid the temptation to micro-zone the place, unless you're willing to pay up front for the buffer tank & controls that allows that to happen without short-cyling the boiler into an early grave.

That said, given the size of the house it's unlikely that the heat load will be above the output of even the smallest oil boilers, but could be well above that of a single heat pump. The very smallest System 2000 oil-burners are about as good as it gets on efficiency, but heat-purging boilers like the MPO-IQ 84 can work about as well if you take the time to set it up correctly. On the low-cost end a Biasi B3 is probably closer to your actual heating load, but doesn't come with the control sophistication of the others. But no oil burner is going to air-condition as well as a heat pump, eh?

If taking a heat pump route, the open zone may be capable of being heated with a single head mini-split, but you may want to use a mini-duct cassette in the basement to serve the bedroom zone. It's important to not oversize a modulating heat pump by very much, since the modulation range isn't infinite. Once they drop into cycling on/off the efficiency falls off significantly, but if it's undersized for the load and running flat-out all the time it's efficiency is even lower. There is a "Goldilocks" range for sizing them, so having the room-by-room heat load calculations in hand is a critical piece of information before embarking on that route.

 

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[Henbogle]

Some parts of Maine are much colder that others, so it's tough to hazard what your 99% outdoor design temp might be, which is relevant to whether or not there are heat pump solutions that work. Got a ZIP code?

Is there basement under all rooms, or just one part of the house? Is the foundation insulated (or going to be), rather than just the foundation sills & band joists? If not, they should be, but don't just slap up a fiberglass insulated studwall or you'll be in the mold-farming biz. (The remodel forum on this site has numerous threads on the subject.

The "right" thing to do would be to run a Manual-J heat load calculation on the "after" picture of the house post-renovations, using aggressive assumptions about air-tightness.

Only when you know the size of the heat load can you pick reasonable solutions. The most common error is to oversize the boiler /furnace/ heat-pump, which cuts into both efficiency & comfort, and sometimes cuts into longevity.

Another important factor for boiler selection is the number of zones, and the amount & type of radiation on each zone. Avoid the temptation to micro-zone the place, unless you're willing to pay up front for the buffer tank & controls that allows that to happen without short-cyling the boiler into an early grave.

That said, given the size of the house it's unlikely that the heat load will be above the output of even the smallest oil boilers, but could be well above that of a single heat pump. The very smallest System 2000 oil-burners are about as good as it gets on efficiency, but heat-purging boilers like the MPO-IQ 84 can work about as well if you take the time to set it up correctly. On the low-cost end a Biasi B3 is probably closer to your actual heating load, but doesn't come with the control sophistication of the others. But no oil burner is going to air-condition as well as a heat pump, eh?

If taking a heat pump route, the open zone may be capable of being heated with a single head mini-split, but you may want to use a mini-duct cassette in the basement to serve the bedroom zone. It's important to not oversize a modulating heat pump by very much, since the modulation range isn't infinite. Once they drop into cycling on/off the efficiency falls off significantly, but if it's undersized for the load and running flat-out all the time it's efficiency is even lower. There is a "Goldilocks" range for sizing them, so having the room-by-room heat load calculations in hand is a critical piece of information before embarking on that route.

 

[Henbogle]

Thanks for your response. Will my plumbing/heating guy know how to calculate the Manual-J heat load?
Regarding insulating the basement, it is currently un-insulated, and is a partial daylight basement, and it does run under the majority of the house; the sunroom is on posts with an insulated crawl space. We do plan to insulate, but sometime in the near future. We are in mid-coast Maine, 04011, more coastal thus a bit warmer/less snow. Marginally.
The house is currently operating on 1 zone; I'd like to put the bedrooms on a separate zone if it is feasible, as they currently seem to be very warm. Most of the house has SlantFin baseboard, and the bedrooms all have a radiator along an entire wall. The bedrooms are all small, 9x11 and 11x14.5 in size.

You totally picked up my heat-pump thinking RE the air conditioning! I'd love some A/C in the summer, but really prefer hot water baseboard. Given what we've already expended in replacing the radiators, I feel like we'd be foolish to ditch the hwbb entirely, too.

 

[Dana]

Brunswick, cold and snowy? I thought that was more like the "Maine Riviera" ( or maybe that's better applied to Old Orchard Beach. ) The 99th percentile temperature bin at the Brunswick Naval Air Station is even in positive digits (+2F)! A typical tightened up insulated 2x4 house with an insulated foundation will come in at about 15 BTU/hr per square foot of conditioned space, so you're probably looking at a design heat load well under 30,000 BTU/hr for the "after" picture, which is well within the output range of a couple of cool climate mini-splits.

The Fujitsu _ _ RLFCD mini-ducted series mini splits have fully rated outputs down to oudoor temps of -5F, the Mitsubishi Hyper Heating series are specified down to -13F, and the Fujitsu _ _ RLS3H wall-coil types are specified down to -15F, so if you wanted to, there IS a mini-split solution possible, and the operating cost would be less than heating with hydronic baseboards and a 3x oversized oil fired boiler. If recent history is any guide you'd be looking at $9-15K for an all mini-split solution if competitively bid. Some will try to sell you on installing a multi-split system with a head in every room, but that's usually more expensive and less efficient than two separate mini-splits, one for the open zone, and a ducted version covering the bedroom zone. Even the smallest heads are oversized for the loads of small bedrooms, and the compressors for multi-splits would then be oversized for the whole bedroom zone load, and would end up spending more time cycling on/off than modulating. But with the room-by-room load numbers this can be sorted out.

The track record of getting getting a decently accurate Manual-J out of HVAC contractors is not a good one. Some do a great job of it, but that's probably 1 out of 20. I suspect fewer than 1 in 5 would even do it as a service, and the rest would only have vague notions of what it's about. The best solution is to bite the bullet and hire an architect or engineer who does it as a service, and is only selling you the accuracy of their calculations, not a heating system. IIRC a contractor posting as BadgerBoilerMN on this site does Manual-Js over the internet if you provide all the information, but it's better if it's done with a site-visit.

If you can't find anyone more local, Rob Brown at Rockport Mechanical (about an hour away from you) would be competent for both the Manual-J and hydronic heating system design (micro-zoned or otherwise.)

If you've swapped out cast-iron radiators for fin-tube baseboard it's usually a step down in comfort, but it buys you back some floor area. But it's also very low thermal mass heat emitters, making micro-zoning more likely to short-cycle the boiler. How many feet of baseboard do you have in what would be the bedroom zone, and how much is there in the rest of the house?

 

[Henbogle]

Maine Riviera, hahahaha.... I lived in Presque Isle for a while and yes, compared to that Brunswick is tropical.

I'm a furnace novice, so the phrase " very low thermal mass heat emitters, making micro-zoning more likely to short-cycle the boiler" is a little over my head. I surmise that short-cycle means running many short cycles, which will wear the boiler components out faster?

we did not replace traditional radiators, the house was originally built with the fin-tube baseboard. We removed some of it and replaced it with Pensiotti towel-warmer style radiators and Smith Environmental toekick and fan-driven convection heaters. If money were no object I'd use all Eureopean wall panel radiators, which I enjoyed while living in Scandinavia for a few years.

 

[Dana]

Thermal mass is a term used to describe how much heat it takes to raise the temperature of an object, which is a function of it's material properties, not just mass/weight. Most of the thermal mass in hydronic heating systems is in the water, which has about 9x the thermal mass per pound of iron or steel, and about 11 x that of copper. Heat emitters like old fashioned cast iron has a substantial amount of thermal mass in both their water volume and iron weight compared to fin-tube convectors.

This becomes important in heating systems when the emitters on a zone can't deliver heat to the room at the same rate that the boiler is putting heat to the system. The more thermal mass there is in the system, the longer it takes for the boiler to hit it's high-limit and turn off when serving a zone that doesn't have enough heat emitter to deliver the whole boiler output to the room.

A cast iron boiler that is cycling on/off with burn times less than 5 minutes per burn (10 minutes is better) will underperform it's tested AFUE efficiency by quite a bit. And you rightly deduced that cycling on/off a LOT will prematurely wear out the boiler's components. AFUE testing presumes an oversizing factor of only 1.7x the design heat load, and sufficient heat emitters to deliver the heat to the zones without excessive cycling.

Given the size of the house, it's likely that almost any oil boiler will be 3-4x the size of the heat load. With sufficient thermal mass in the system and some smarter controls a ridiculously oversized boiler can still operate with reasonable efficiency, but it may be easier to do something else. A tank-type propane fired combi-heater like the HTP Versa Hydro or Flame has the full thermal mass of the tank of hot water to work with, which is an order of magnitude more thermal mass than you have in a fin-tube baseboard system with a small modern oil boiler. These may be a reasonable choice here if you're dedicated to heating with the baseboards. Despite the higher fuel cost per BTU of propane vs. oil, the higher steady-state efficncy and lack of short-cycling makes the operating cost comparable, sometime smaller.

But I'm not beyond going for an all mini-split solution for a modest-load house like this. As uncomfortable and drafty as traditional noisy oversized forced hot air can be, modulating heat pumps are in a different class. Fin tube baseboards aren't nearly as comfortable as radiators, because they are convectors, delivering almost all of the heat as convecting hot air, with but a tiny fraction of the heat delivered as direct radiation. This isn't particularly more comfortable than a right sized mini-split solution, and they don't air condition. (I even set up my own mother with an all mini-split solution, and she's still talking to me 3+ years later. ) Mini-splits have it WAY over air-coils like toe-kick heaters too.

There are modulating hydronic air source heating/cooling chillers that could probably cover you too (say, a 2-ton Chilltrix), but you'd need something other than fin-tube for heat emitters, since they won't operate with as much efficiency or capacity at the water temperatures you'd need to get the heat into the rooms with fin-tube. (Radiant floors and panel radiators can work though.) It takes a competent designer too, not always in good supply. (Rob Brown has done hydronic air source heat pump solutions using Daikin equipment and radiant floors, but that too is pretty pricey.)

 

[Henbogle]

Thanks so much for these very clear explanations. This will help me be much more comfortable when locating installers. I will give Rob Brown a call, I have relatives in Rockland so it may be we know some mutual people. I am also quite interested in the Versa combo heaters you suggested, so I'll be doing some reading up on those tonight. Thanks again!

 

[Tom Sawyer]

If you stick with oil, Dana mention system 20000 which is an excellent choice. Also Biasi is an excellent three pass, cast iron boiler that is fairly inexpensive. In the high end Buderus makes a fine three pass cast iron also. On the very high end is the Firebird condensing oil fired which is impressive as hell but pricey.

 

[Dana]

This is a pipsqueak whole house load microzoned down to mouse-whisker zone loads which makes a System 2K solution bordering on insane. (Note, I also mentioned the Biasi B3, but even that's ~3x oversized for the whole house load.)

If sticking with oil it makes more sense to micro-zone it off a Bock hot water heater, with a plate heat exchanger isolating the heating water from the potable than installing a 4x oversized System 2K only to short cycle it to death on zone calls.

But if you're going to add air conditioning, a mini-split heat pump solution that does it all is a lower up-front investment than boiler + AC, and will cost less to heat with than oil.

 

[Tom Sawyer]

I don't think it's that small. It's had a big master bath and a sun room added and they want to use the basement as well. I'd off the cuff estimate the loss at about 55,000

 

[Henbogle]

The house is 1330 square feet, including the additions of sunroom and master bath. The area in the basement we hope to finish is currently partially finished and has a Jotul propane stove installed for supplemental heat.

Unfortunately, we don't have access to natural gas, it is infuriatingly close, but not close enough at one street over.

While adding a/c would be nice, it is not a priority at this time. The timing of the boiler failure is forcing our hand and having just spent gazillions on renovations, we are feeling the need to be frugal. Our original plan was to look at a solar system in a few years.

 

[Henbogle]

Here is the first quote I've received -- by text, with a more complete quote to follow. This is from the heating/plumbing contractor who did all the work on the house for the renovation, and who I have been pleased with to date.

Replacement Boiler: 4 section 3 pass Biasi cast iron boiler with 140 psi Reillo burner, coupled with indirect fired boiler for download. Complete job would be $6573.00.

I'm not sure what the indirect fired boiler for download means? I am meeting with another contractor this afternoon for a quote and I'd love to understand this to be able to ask slightly better questions!

If any of you can recommend a good article "heating for dummies" for me to read in the meantime, I'd appreciate it. I'm trying to squeeze all this research in at a crazy time of year!

 

[Dana]

Tom, 55K @ +2F, seriously? For 1330' total space? Maybe, with some of the windows open in the sunroom! Reality is something like half that, possibly less.

The 4-plate Biasi is WAY bigger than you need, with it's DOE output of 110,000 BTU/hr it would be about 4x oversized for your likely load. The B-3 would be more appropriately size though still at least 2x oversized) ESPECIALLY if you're going to break it up into zones, with a DOE output of 67K, and would even cover Tom's Mars-stratosphere high estimate of 55,000 BTU/hr even if the boiler were installed outside of conditioned space, with it's 58K IBR net output:

To perfectly balance 67K of boiler output (the 3-section unit, not the 4) requires about 120' of baseboard. To not short-cycle it too badly on zone calls would require something like 80' of baseboard on the smallest zone. It only gets worse if you bump it up to the 4 section boiler. If I had to guess I'd hazard that the whole house probably doesn't even have 80' of baseboard, but measure it all up, and tell us which model towel racks & toe-kicks etc you have added.

The "indirect fired boiler for download" sounds like dialect- is the contractor from strange place like the UK or Canuckistan? What it means in 'merican is an indirect fired hot water heater- a tank of hot water that is heated by the boiler with a heat exchanger isolating the potable water from the heating system water:

With an indirect water heater operated as the "priority zone" (= thermostat calls for heat from the other zones are suppressed whenever the water heater is being heated) you won't have any domestic hot water capacity issues even with the smallest boiler. If there's a monster-sized spa to fill in the master bath upsize the volume of the indirect tank, not the boiler.

 

[Henbogle]

Very helpful, thanks. So I should ask about a smaller boiler. Is there any benefit to switching to an electric HW heater versus the oil fired heater? That way the oil burner would be on vacation 5 months of the year.

And is there any benefit to adding a separate zone for the bedrooms? Or am I better off to keep the doors closed and the thermostat set lower in the main part of the house?

We have 2 shower-only baths, a Bosch dishwasher and a Bosch washer, so pretty low consumption of hot water. No spas or hot tubs.

 

[Dana]

Very helpful, thanks. So I should ask about a smaller boiler. Is there any benefit to switching to an electric HW heater versus the oil fired heater? That way the oil burner would be on vacation 5 months of the year.

And is there any benefit to adding a separate zone for the bedrooms? Or am I better off to keep the doors closed and the thermostat set lower in the main part of the house?

We have 2 shower-only baths, a Bosch dishwasher and a Bosch washer, so pretty low consumption of hot water. No spas or hot tubs.

You might consider installing a heat pump water heater in the basement near the boiler. A current model heat pump water heater gets about 2/3 of it's heat out of the room it's in, so in winter it's lowering the temperature of the boiler room which lowers the heat loss out of that room by lowering the room temp a degree or two. That's essentially scavenging the jacket losses of the boiler as heat for the hot water.

And during the shoulder seasons & summer when the air is more humid, a heat pump water heater is getting most of it's heat from the heat of vaporization of the moisture in the air- it dehumidifies the basement air, but without raising the basement temperature, which is exactly what you want in an New England basement from May through October when the outdoor air's dew point is near the temperature of the basement slab. If you normally run a room dehumidifier in the basement to keep the musty-basement smell under control, a heat pump water heater would be carrying the bulk of that load.

If it were my house and I wasn't on the gas grid I'd go this route- taking a chance on the 4th generation GE GeoSpring heat pump water heaters, which have (apparently) solved the early revision product problems, and have bumped up to higher in efficiency, with EFs it the 3s rather than the low 2s.

The advantage of zoning is primarily for comfort, but it complicates the system design when the smallest boiler is ridiculously oversized for any single zone. If you can achieve reasonable temperature balance without breaking it up into zones it's nicer to the boiler. If the boiler were smaller or could modulate down to a firing rate reasonable for smaller zones there would be an efficiency advantage too, but modulating boilers add quite a bit to the installed price. If breaking it up into zones think seriously about using a hot water heater, to avoid the short cycling problem. It doesn't have to be as big & sophisticated as a modulating HTP Versa. It's pretty straightforward to design a micro-zoned heating system around an oil-fired hot water heater, if oil is your first choice (currently cheaper heat than propane.)

If going the oil-fired hot water heater combi-route, a ~100-125,000 BTU/hr burner isn't a bad idea, since you can't isolate the heating function from the hot water function, and on a cold day a long shower could outstrip the output capacity of the smallest oil hot water heater burners unless you got into the habit of turning the thermostats down before stepping into the shower. (If you installed a drainwater heat exchanger for the shower you could probably do OK with the smallest ones, but that requires more analysis. )

 

[Dana]

BTW: DO go around and measure up all of the baseboard in the house, since that determines just how likely you are to short-cycle any proposed boiler.

Look up the specs on the boiler and divide the DOE output BTUs by the the running length of baseboard. If that number is anything over 600 BTU per foot it's going to need more analysis, and you definitely DON'T want to break it up into smaller zones without careful consideration. If it's under 450 BTU/ft it may need some commonly-done near boiler plumbing tweaks to keep the boiler happy.

The very smallest oil-burners out there don't go much below 60,000 BTU/hr (or 60 MBH- same thing ) for DOE output, which means ideally your system has at LEAST 100' of baseboard. But that's not usually the case in a 1330' house, so it's good to know what the real number is.

 

[Tom Sawyer]

I would opt for the three section as well. Down fired it will occasionally short cycle but an outdoor reset control would tame most of that as well. It's not going to be possible to match the heat loss using oil equipment however, there is a sun room involved and I'm guessing it's mostly glass so that will add considerably to the loss.

 

[Henbogle]

I measured tonight and we have about 80 feet of fin tube baseboard, 2 Pensotti towel warmer radiators, 24x30 @ 1584 BTUs and 24x48 @ 2464BTUs, a Smith Environmental toekick heater model #KS2004, and PSU 23 wall mounted fan convector.
We learned tonight that we will need to replace and relocate the oil tank to meed current code if we choose an oil fired system. This guy said in our situation, he would recommend a propane boiler with an indirect water heater due to the additional costs of the oil tank replacement.

 

[Dana]

You have enough heat emitter to balance with the output of the B-3 if operated as a single zone, but not the B-4. The towel warmers add up to the equivalent of ~7' of baseboard, the Smith is the equivalent of ~8', the big fan convector maybe 25-30', so added to the 80' of actual fin-tube it's like having ~125-130' of fin tube.

If you went with the 4 plate boiler, 110,000 BTU/130' = 846 BTU/hr per foot of emitter, which would require an average water temp north of 220F to balance emitter output to boiler input. Even if it's a boiler that can be run at 240F (I haven't looked it up), the distribution & standby losses would be enormous, for a much degraded system efficiency.

With the 3-plater, 67,000 BTU/130' = 515 BTU/hr per foot, which balances at an AWT of about 170F (180F out of the boiler, 160F returning), which is fine.

A heat pump water heater will be cheaper hot water than a propane boiler with an indirect, but it may still make sense to just go with the smallest condensing HTP Versa, (a fully-integrated well engineered system) rather than a propane boiler + indirect. Cost-wise they may be similar, but the Versa has lower system design risk and faster installation. (It could probably be installed in a day if you're not changing the zoning.)