Got my new Burnham FCM120 mod-con gas boiler today.

[flamegrabber]

And I'm not sure it's going to do the job.

It's the Burnham FCM120 with a DOE MBH rating of 107000 and an outdoor reset. Gross BTU output is 120000 ( hence the model number ).

The plumber, who determined that would be enough BTU's for the house did so by adding up the linear feet of FHW radiators in the house.

But I looked at the spec plate on my current Burnham oil boiler and it has a DOE rating of 156000.

Quite a difference but then again the new boiler is 95.2% efficient in perfect conditions and the existing oil burner is at best 80% efficient and 17 years old on top of that.

A full blown heat loss study was not done. The house has new Energy Star windows amd new doors. Ceiling insulation could be better but there is some up in the attic.

My house is a small ranch with with a full basement.

Both floors total just under 1800 sq feet and the house has 84' of FHW radiators.

Can anyone give me their opinion on whether this may be enough to do the job?

The climate is the Northshore of Massachusetts.

Thanks alot,

FG.

 

[Chris S]

You can do the heatloss yourself, use the Slantfin calculator, it doesnt take long. Keep in mind the heatin industry has oversized equipment for years. That boiler could very well be more than adequate for your needs. In my area we design for 0 degree outside temp and 70 inside. I have that same boiler heating a 4200 s.f. home. Granted it's new construction, R-21 walls, R-38 above, and well built, but the days of great big boilers are coming to an end.
I just calculated heat loss on my own new home- 2500s.f. - 9' & 12' ceilings , ranch (read higher heat loss) total heat loss 62,000 btu on the design day

Chris
You are going to like that boiler- they purr.

 

[flamegrabber]

Thanks Chris for the info.

I read today that as long as my current baseboards heat the house well enough at boiler temps below 200* ( it's set to 180* ) that it should be fine since we're plumbing the new FCM120 into the existing baseboards.

True?

I'm pretty sure the oil burner I have now was purchased oversized. The house used to be my mothers and she bought the boiler 17 years ago by the same oil company she bought oil from, so I think it's possible they took advantage of her since I was living in another state at the time and couldn't help with her decision.

I can't imagine the largest gas boiler in that model ( the Burnham FCM120 ) wouldn't heat an 1800 sq ft house. The house was built in 1948 and has had insulation added to the attic many years ago, all new Energy Star rated windows installed in the last 3 years, brand new doors, etc.

So it's alot tighter than it was a just few years ago. I remember the windows were all loose and used to rattle.

The oil boiler is 17 years old and was probably ~80% efficient when it was new, and I read that they become less efficient the older they get.

So the new Burnham NG FCM120 mod-con will be much more efficient than the oiler.

Thanks Chris,

FG.

You can do the heatloss yourself, use the Slantfin calculator, it doesnt take long. Keep in mind the heatin industry has oversized equipment for years. That boiler could very well be more than adequate for your needs. In my area we design for 0 degree outside temp and 70 inside. I have that same boiler heating a 4200 s.f. home. Granted it's new construction, R-21 walls, R-38 above, and well built, but the days of great big boilers are coming to an end.
I just calculated heat loss on my own new home- 2500s.f. - 9' & 12' ceilings , ranch (read higher heat loss) total heat loss 62,000 btu on the design day

Chris
You are going to like that boiler- they purr.

 

[Chris S]

Do you have 84' of baseboard heat? New 3/4" copper fin tube baseboard we install is generally figured at 600-700 btu/ lineal ft at 180 degrees. Heat loss calculations aside, this is the maximum amount of heat you will be able to take away from any boiler. The good news is the boiler will match the load, and so not short cycle. Also, don't feel bad if it is oversized, there is a very small price difference between the 120 and the smaller models.
Keep in mind that boiler has a built in priority for domestic hot water, so you do not oversize to accomodate for your hot water needs. Additionally, you should take advantage of the DHW priority, --you have to if using the outdoor reset otherwise in moderate weather the temps may be too low for DHW.
Don't forget the condensate neutralizer.

Chris

 

[flamegrabber]

Yep, 84 feet of baseboard total of all the rooms.

I'm buying a seperate tankless/on-demand domestic hot water heater because there's only 2 of us in the house.

And I'm got the new FCM120 for $999.99 from National Grid because I'm a conversion from oil, so it's a great price for the boiler.
It's in the box in my basement now ready for install this coming Friday.

Not sure about all the tech stuff you mention but I'll pass it on to the plumber. I think this is his first mod-con install but he's good. And I read it's not a difficult install if you follow the manual.

I definitaly want to take advantage of the outdoor-reset.

I'll mention all this to him.

What is the condensate neutralizer? The pump? He did say something about a small pump being necessary for the condensation.

I did want some overhead on the new boiler incase we ever do an addition in the house.

Thanks again Chris,

FG.

Do you have 84' of baseboard heat? New 3/4" copper fin tube baseboard we install is generally figured at 600-700 btu/ lineal ft at 180 degrees. Heat loss calculations aside, this is the maximum amount of heat you will be able to take away from any boiler. The good news is the boiler will match the load, and so not short cycle. Also, don't feel bad if it is oversized, there is a very small price difference between the 120 and the smaller models.
Keep in mind that boiler has a built in priority for domestic hot water, so you do not oversize to accomodate for your hot water needs. Additionally, you should take advantage of the DHW priority, --you have to if using the outdoor reset otherwise in moderate weather the temps may be too low for DHW.
Don't forget the condensate neutralizer.

Chris

 

[Chris S]

You can make, or buy a neutralizer for the condensate. The condensate will be aggressive out of the unit.
It is corrosive to cast iron & concrete
do a search on this
Chris

 

[flamegrabber]

His initial response was to pump it into the septic tank, either through the kitchen or the bathroom plumbing.

Would this condensate be harmful using these methods?

If so where else can it be pumped/expelled? He said code wouldn't allow it to be pumped out into the yard.

Thanks alot for your great info. I wasn't sure I'd get any info on this unit here but I did.

FG.


[quote author="Chris S" date="1225780955"
]You can make, or buy a neutralizer for the condensate. The condensate will be aggressive out of the unit.
It is corrosive to cast iron & concrete
do a search on this
Chris[/quote]

 

[BrownianHeatingTech]

You do not want an oversized condensing boiler.

If it is oversized, it won't condense, and you won't get that high efficiency from it.

You're going to have minimal enough condensing operation with baseboard, anyway, so you want to have the boiler sized as accurately as possible.

Check your heat loss before installing. Based upon your square footage, it's very likely that it is oversized, and you will want to rectify that before installing, rather than after, if it's actually the case.

Joe

 

[flamegrabber]

I agree with you.

But the FCM120 is still quite a bit smaller than the oiler it's replaceing. The oiler has a DOE MBH rating of 156 and a IBR water rating of 136.

The FCM120 has a DOE rating of 107 MBH and a IBR rating of 93.

Also, the new boiler is a MOD-con boiler. It can modulate the heat down to where it can continue to condense.

i.e.:

Oversizing

We do not suffer from real temperature extremes in this country — with the exception of the odd summer heat wave — so there is usually plenty of spare capacity in our heating plant.

The industry has been rightly criticised for oversizing boilers in the past often by as much as 50%. This is normally as a result of the system designer understandably erring on the side of caution — although a 50% err is a big one! However, oversizing condensing boilers is less of an issue as they can modulate down to reduce return temperatures and so stay in condensing mode for longer.

This capability is not an excuse for continued miscalculation, but a further factor for engineers to consider when matching boiler plant to likely demand conditions.

Not only is the market ready for change, thanks to a combination of external and internal factors, but it is also evolving into a state where the best engineers have a chance to show their quality. The advent of Competent Person Schemes and quality initiatives like CIBSE’s register of Low Carbon Consultants shows that the market conditions are now right for excellence to rise to the top.

Heating-equipment manufacturers must work more closely with design engineers than ever to ensure systems are configured to meet these more challenging, but very welcome, developments.

John Bailey is technical manager for Vaillant Applied Systems’ commercial heating division, Vaillant House, Medway City Estate, Trident Close, Rochester, Kent ME24 4EZ.

You do not want an oversized condensing boiler.

If it is oversized, it won't condense, and you won't get that high efficiency from it.

You're going to have minimal enough condensing operation with baseboard, anyway, so you want to have the boiler sized as accurately as possible.

Check your heat loss before installing. Based upon your square footage, it's very likely that it is oversized, and you will want to rectify that before installing, rather than after, if it's actually the case.

Joe

 

[BrownianHeatingTech]

But the FCM120 is still quite a bit smaller than the oiler it's replaceing. The oiler has a DOE MBH rating of 156 and a IBR water rating of 136.

The FCM120 has a DOE rating of 107 MBH and a IBR rating of 93.

That's really not relevant. I see boilers and furnaces that are two to three times the size they actually need to be, on a regular basis.

Also, the new boiler is a MOD-con boiler. It can modulate the heat down to where it can continue to condense.

According to Burnham, it has 3:1 modulation. So, call it 107MBh to 36MBh.

Let's imagine that your house has a peak load of 56MBh, which could easily be the case based upon your description. That will translate to an average load of roughly 28MBh. So, for more than half the heating season, the boiler would be short-cycling on it's lowest modulation, and still be oversized.

Also, just because a boiler can be modulated to maintain condensing operation, doesn't mean it will. Few boilers have the control logic to do so. Most rely on "dumb" temperature control based solely upon outdoor reset, not return water temperature.

Joe

 

[flamegrabber]

I'd bet most mod-con boilers don't use a closed loop control system based on the outdoor reset temp to maintain constant or near constant condensing because they don't need to, or like you said it would be a very expensive and more complex control system - a rare piece of equipment.

As I understand it, the outdoor reset temp readback is used, with the thermostat setting, to modulate and maintain the heating water temp sent to the rads, not the return water temp. That's why it doesn't always condense.

Condensing is based on the return temp differential, no?

In any case, I bought the 120 based on the size of the oiler it's replacing, and the fact that we may want to put on a 2nd floor for a total of 3. That would add another 900 sq ft for a total of 2700.

And the fact that even with the new windows and doors, the house consumed 1150 gallons of oil last year.

That's alot of oil for a house with just under 1800 sq ft and 84' of FHW radiation. But that does include hot water.

If you take away 365 gallons of oil for hot water, 1 per day, that leaves 785 for the FHW heat.

Can you wag how much MBH that is?

Last January was my worst month for oil. 206 gallons that month alone.

Yikes.

Thanks,

FG.



Also, just because a boiler can be modulated to maintain condensing operation, doesn't mean it will. Few boilers have the control logic to do so. Most rely on "dumb" temperature control based solely upon outdoor reset, not return water temperature.

But the FCM120 is still quite a bit smaller than the oiler it's replaceing. The oiler has a DOE MBH rating of 156 and a IBR water rating of 136.

The FCM120 has a DOE rating of 107 MBH and a IBR rating of 93.

That's really not relevant. I see boilers and furnaces that are two to three times the size they actually need to be, on a regular basis.

Also, the new boiler is a MOD-con boiler. It can modulate the heat down to where it can continue to condense.

According to Burnham, it has 3:1 modulation. So, call it 107MBh to 36MBh.

Let's imagine that your house has a peak load of 56MBh, which could easily be the case based upon your description. That will translate to an average load of roughly 28MBh. So, for more than half the heating season, the boiler would be short-cycling on it's lowest modulation, and still be oversized.

Also, just because a boiler can be modulated to maintain condensing operation, doesn't mean it will. Few boilers have the control logic to do so. Most rely on "dumb" temperature control based solely upon outdoor reset, not return water temperature.

Joe

 

[BrownianHeatingTech]

I'd bet most mod-con boilers don't use a closed loop control system based on the outdoor reset temp to maintain constant or near constant condensing because they don't need to, or like you said it would be a very expensive and more complex control system - a rare piece of equipment.

As I understand it, the outdoor reset temp readback is used, with the thermostat setting, to modulate and maintain the heating water temp sent to the rads, not the return water temp. That's why it doesn't always condense.

Condensing is based on the return temp differential, no?

Condensing is based upon the absolute return temp. If it's below 140, condensation will occur. If it's below 120, condensation will occur reliably. Achieving that is hard enough with baseboard heat, let along with baseboard heat and an oversized boiler.

In any case, I bought the 120 based on the size of the oiler it's replacing, and the fact that we may want to put on a 2nd floor for a total of 3. That would add another 900 sq ft for a total of 2700.

And the fact that even with the new windows and doors, the house consumed 1150 gallons of oil last year.

That's alot of oil for a house with just under 1800 sq ft and 84' of FHW radiation. But that does include hot water.

If you take away 365 gallons of oil for hot water, 1 per day, that leaves 785 for the FHW heat.

Can you wag how much MBH that is?

Your baseboard length determines the maximum amount of energy that can be transferred. 500-600 btuh per linear foot of element, depending upon the brand and size. Even if the baseboard is high-output stuff and just barely long enough to heat your house (ie, not oversized at all), your maximum load is 50,400 btuh. You could put a million-btu boiler in there, and it couldn't transfer more heat than that. So your previous boiler was dramatically oversized.

And your mod-con will not be doing much condensing at all.

If we assume that worst-case scenario with the baseboard, and use your given area of 1800 sf, you have a heat loss of 28 btuh/sf. Even assuming that your addition is built to the same efficiency (newer construction will tend to be better-built, but let's assume a worst-case scenario), your total heat load would only be 75,600 btuh.

It's certainly your choice, but it if were me, I'd look at swapping boilers.

I'd also recommend looking into the Honeywell AQ2000-series boiler controls. They use room temperature sensors to actually monitor the zones (rather than simple on-off data from thermostats), and will synchronize zone operation. That can help mitigate some of the oversizing, by forcing zones to operate at the same time, as often as possible (thereby increasing the load that the boiler "sees").

Joe

 

[flamegrabber]

Thanks Joe for the info.

Can you answer this question?:

How much extra efficiency is acheived during condensing?

The 120 says maximum possible is 95.2.

How much of that is contributed by the condensing?

The boiler cost me $999.95 from National Grid because I'm a new oil convert.

Thanks again,

FG.

I'd bet most mod-con boilers don't use a closed loop control system based on the outdoor reset temp to maintain constant or near constant condensing because they don't need to, or like you said it would be a very expensive and more complex control system - a rare piece of equipment.

As I understand it, the outdoor reset temp readback is used, with the thermostat setting, to modulate and maintain the heating water temp sent to the rads, not the return water temp. That's why it doesn't always condense.

Condensing is based on the return temp differential, no?

Condensing is based upon the absolute return temp. If it's below 140, condensation will occur. If it's below 120, condensation will occur reliably. Achieving that is hard enough with baseboard heat, let along with baseboard heat and an oversized boiler.

In any case, I bought the 120 based on the size of the oiler it's replacing, and the fact that we may want to put on a 2nd floor for a total of 3. That would add another 900 sq ft for a total of 2700.

And the fact that even with the new windows and doors, the house consumed 1150 gallons of oil last year.

That's alot of oil for a house with just under 1800 sq ft and 84' of FHW radiation. But that does include hot water.

If you take away 365 gallons of oil for hot water, 1 per day, that leaves 785 for the FHW heat.

Can you wag how much MBH that is?

Your baseboard length determines the maximum amount of energy that can be transferred. 500-600 btuh per linear foot of element, depending upon the brand and size. Even if the baseboard is high-output stuff and just barely long enough to heat your house (ie, not oversized at all), your maximum load is 50,400 btuh. You could put a million-btu boiler in there, and it couldn't transfer more heat than that. So your previous boiler was dramatically oversized.

And your mod-con will not be doing much condensing at all.

If we assume that worst-case scenario with the baseboard, and use your given area of 1800 sf, you have a heat loss of 28 btuh/sf. Even assuming that your addition is built to the same efficiency (newer construction will tend to be better-built, but let's assume a worst-case scenario), your total heat load would only be 75,600 btuh.

It's certainly your choice, but it if were me, I'd look at swapping boilers.

I'd also recommend looking into the Honeywell AQ2000-series boiler controls. They use room temperature sensors to actually monitor the zones (rather than simple on-off data from thermostats), and will synchronize zone operation. That can help mitigate some of the oversizing, by forcing zones to operate at the same time, as often as possible (thereby increasing the load that the boiler "sees").

Joe

 

[BrownianHeatingTech]

Thanks Joe for the info.

Can you answer this question?:

How much extra efficiency is acheived during condensing?

The 120 says maximum possible is 95.2.

How much of that is contributed by the condensing?

The boiler cost me $999.95 from National Grid because I'm a new oil convert.

Non-condensing boilers operate in the 80-85% efficiency range, and that's basically what you'd have if you were not in condensing operation. They also draw less electrical power, and require less maintenance than condensing boilers, so you would have added expenses, without the benefit of increased fuel efficiency.

Joe

 

[Chris S]

I think that boiler claims 89 or 90% non condensing

 

[flamegrabber]

Joe,

I don't understand this:

"Condensing is based upon the absolute return temp. If it's below 140, condensation will occur. If it's below 120, condensation will occur reliably. Achieving that is hard enough with baseboard heat, let along with baseboard heat and an oversized boiler."

What difference does the boiler size make? It sounds like it's all up to the rad length to me.

The water temp leaving the boiler for the rads will be the same no matter what size boiler it is, no?

And it's the radaitors that cool the water, and it's the return temp that determines whether or not it will condense.

The water temp SENT to the radiators will be the same no matter what the boiler size is.

I can see that if bigger boilers meant higher water temps to the rads, that would mean higher return temps from the rads, but I don't think the water temps to the rads will be any different based on boiler size.

What am I missing here?

Thanks,

FG.

Thanks Joe for the info.

Can you answer this question?:

How much extra efficiency is acheived during condensing?

The 120 says maximum possible is 95.2.

How much of that is contributed by the condensing?

The boiler cost me $999.95 from National Grid because I'm a new oil convert.

Thanks again,

FG.

I'd bet most mod-con boilers don't use a closed loop control system based on the outdoor reset temp to maintain constant or near constant condensing because they don't need to, or like you said it would be a very expensive and more complex control system - a rare piece of equipment.

As I understand it, the outdoor reset temp readback is used, with the thermostat setting, to modulate and maintain the heating water temp sent to the rads, not the return water temp. That's why it doesn't always condense.

Condensing is based on the return temp differential, no?

Condensing is based upon the absolute return temp. If it's below 140, condensation will occur. If it's below 120, condensation will occur reliably. Achieving that is hard enough with baseboard heat, let along with baseboard heat and an oversized boiler.

In any case, I bought the 120 based on the size of the oiler it's replacing, and the fact that we may want to put on a 2nd floor for a total of 3. That would add another 900 sq ft for a total of 2700.

And the fact that even with the new windows and doors, the house consumed 1150 gallons of oil last year.

That's alot of oil for a house with just under 1800 sq ft and 84' of FHW radiation. But that does include hot water.

If you take away 365 gallons of oil for hot water, 1 per day, that leaves 785 for the FHW heat.

Can you wag how much MBH that is?

Your baseboard length determines the maximum amount of energy that can be transferred. 500-600 btuh per linear foot of element, depending upon the brand and size. Even if the baseboard is high-output stuff and just barely long enough to heat your house (ie, not oversized at all), your maximum load is 50,400 btuh. You could put a million-btu boiler in there, and it couldn't transfer more heat than that. So your previous boiler was dramatically oversized.

And your mod-con will not be doing much condensing at all.

If we assume that worst-case scenario with the baseboard, and use your given area of 1800 sf, you have a heat loss of 28 btuh/sf. Even assuming that your addition is built to the same efficiency (newer construction will tend to be better-built, but let's assume a worst-case scenario), your total heat load would only be 75,600 btuh.

It's certainly your choice, but it if were me, I'd look at swapping boilers.

I'd also recommend looking into the Honeywell AQ2000-series boiler controls. They use room temperature sensors to actually monitor the zones (rather than simple on-off data from thermostats), and will synchronize zone operation. That can help mitigate some of the oversizing, by forcing zones to operate at the same time, as often as possible (thereby increasing the load that the boiler "sees").

Joe

 

[BrownianHeatingTech]

Joe,

I don't understand this:

"Condensing is based upon the absolute return temp. If it's below 140, condensation will occur. If it's below 120, condensation will occur reliably. Achieving that is hard enough with baseboard heat, let along with baseboard heat and an oversized boiler."

What difference does the boiler size make? It sounds like it's all up to the rad length to me.

The water temp leaving the boiler for the rads will be the same no matter what size boiler it is, no?

And it's the radaitors that cool the water, and it's the return temp that determines whether or not it will condense.

The water temp SENT to the radiators will be the same no matter what the boiler size is.

I can see that if bigger boilers meant higher water temps to the rads, that would mean higher return temps from the rads, but I don't think the water temps to the rads will be any different based on boiler size.

What am I missing here?

Think of it as analogous to driving a car. You want to go 65 on the highway.

Unfortunately, your gas pedal is stuck, so you can only have "all" or "nothing." Now try and drive a steady 65. The only way to get close would be to hit the gas, wait until you go to 75, shut the engine off and coast until you hit 55, then re-start the engine and do it again. That's a conventional non-modulating boiler.

You take your car to a mechanic, who can't fix it right, but gets you some control: now you can get control from full throttle down to 1/3 throttle, but nothing below that except all the way off. Unfortunately, your car only needs 10% throttle to drive 65, so what you have to do now is to drive at 1/3 throttle until you hit 70, then shut the engine off and coast down to 60, etc... That's a modulating boiler.

Now try driving each car at 35, in town...

A "true" modulating boiler that could go anywhere from 0% to 100% would have no trouble maintaining the exact temp that you want. Unfortunately, the throttle is sticky, and it won't operate below a certain point. That means that, unless the minimum level is well below the operating range, you are going to be cycling the flame instead of modulating it. Which is why you want the heat load well up into the operating range of the boiler (in your case, you need 75MBh max, at an estimate). That gives you the widest range of throttle motion to try and keep the "speed" where you want it, instead of cycling.

Joe

 

[flamegrabber]

I beleive the only difference mod-con boiler size makes is in the dynamic range of it's modulation.

That's the difference.

Not the water temp. The output water temp should be the same no matter what the boiler size. Boiler size in that respect is only relelvent when it comes to volume of water, and you can only pump so much water through the number of zones you have plumbed in.

It will make a difference in cost/efficiency regarding heating "MORE" water and heating a larger exchanger, but, be the boiler small or large, both only heat the water to the same temps.

FG.

Thanks Joe for the info.

Can you answer this question?:

How much extra efficiency is acheived during condensing?

The 120 says maximum possible is 95.2.

How much of that is contributed by the condensing?

The boiler cost me $999.95 from National Grid because I'm a new oil convert.

Non-condensing boilers operate in the 80-85% efficiency range, and that's basically what you'd have if you were not in condensing operation. They also draw less electrical power, and require less maintenance than condensing boilers, so you would have added expenses, without the benefit of increased fuel efficiency.

Joe

 

[flamegrabber]

I understand.

I think it'll do some condensing in the coldest months but not alot.

And I have read that these boilers are more efficient than non-condensing ones even when they aren't condensing.

By your calculations even the smaller unit(s) wouldn't suffice. They would condense just a bit more than the 120.

We'll see. I"ll be watching that condensate output.

Thanks again,

FG.

Joe,

I don't understand this:

"Condensing is based upon the absolute return temp. If it's below 140, condensation will occur. If it's below 120, condensation will occur reliably. Achieving that is hard enough with baseboard heat, let along with baseboard heat and an oversized boiler."

What difference does the boiler size make? It sounds like it's all up to the rad length to me.

The water temp leaving the boiler for the rads will be the same no matter what size boiler it is, no?

And it's the radaitors that cool the water, and it's the return temp that determines whether or not it will condense.

The water temp SENT to the radiators will be the same no matter what the boiler size is.

I can see that if bigger boilers meant higher water temps to the rads, that would mean higher return temps from the rads, but I don't think the water temps to the rads will be any different based on boiler size.

What am I missing here?

Think of it as analogous to driving a car. You want to go 65 on the highway.

Unfortunately, your gas pedal is stuck, so you can only have "all" or "nothing." Now try and drive a steady 65. The only way to get close would be to hit the gas, wait until you go to 75, shut the engine off and coast until you hit 55, then re-start the engine and do it again. That's a conventional non-modulating boiler.

You take your car to a mechanic, who can't fix it right, but gets you some control: now you can get control from full throttle down to 1/3 throttle, but nothing below that except all the way off. Unfortunately, your car only needs 10% throttle to drive 65, so what you have to do now is to drive at 1/3 throttle until you hit 70, then shut the engine off and coast down to 60, etc... That's a modulating boiler.

Now try driving each car at 35, in town...

A "true" modulating boiler that could go anywhere from 0% to 100% would have no trouble maintaining the exact temp that you want. Unfortunately, the throttle is sticky, and it won't operate below a certain point. That means that, unless the minimum level is well below the operating range, you are going to be cycling the flame instead of modulating it. Which is why you want the heat load well up into the operating range of the boiler (in your case, you need 75MBh max, at an estimate). That gives you the widest range of throttle motion to try and keep the "speed" where you want it, instead of cycling.

Joe

 

[BrownianHeatingTech]

I understand.

I think it'll do some condensing in the coldest months but not alot.

And I have read that these boilers are more efficient than non-condensing ones even when they aren't condensing.

By your calculations even the smaller unit(s) wouldn't suffice. They would condense just a bit more than the 120.

During the coldest months, the supply water temperature will be higher, meaning the return water temperature will be too high to condense.

Basically, any boiler can be efficient during the coldest period of the year. High-efficiency boilers save fuel during the shoulder seasons. If they are sized correctly, or as close to correctly as possible.

Joe

 

[flamegrabber]

Especially with the outdoor reset.

Gotcha.

FG.

I understand.

I think it'll do some condensing in the coldest months but not alot.

And I have read that these boilers are more efficient than non-condensing ones even when they aren't condensing.

By your calculations even the smaller unit(s) wouldn't suffice. They would condense just a bit more than the 120.

During the coldest months, the supply water temperature will be higher, meaning the return water temperature will be too high to condense.

Basically, any boiler can be efficient during the coldest period of the year. High-efficiency boilers save fuel during the shoulder seasons. If they are sized correctly, or as close to correctly as possible.

Joe

 

[flamegrabber]

Too bad the return water couldn't be cooled to ~120* just before it reentered the boiler.

Then there'd be alot of reliable condensing.

FG.

I understand.

I think it'll do some condensing in the coldest months but not alot.

And I have read that these boilers are more efficient than non-condensing ones even when they aren't condensing.

By your calculations even the smaller unit(s) wouldn't suffice. They would condense just a bit more than the 120.

During the coldest months, the supply water temperature will be higher, meaning the return water temperature will be too high to condense.

Basically, any boiler can be efficient during the coldest period of the year. High-efficiency boilers save fuel during the shoulder seasons. If they are sized correctly, or as close to correctly as possible.

Joe

 

[flamegrabber]

Well, I went to SlantFin and did the heat loss worksheet.

It came up with total btu's of 78000.

Joe, why is that number halved, from your posts yesterday it looks like you cut that number in half???

You said I'd need some 56000 and that would average 28000. I don't understand that calculation.

After that I had it suggest a boiler and it suggested the Victory II VHS-120.

Pretty close to the Burnham FCM120 in terms of specs.

Victory = 120 input, 100 DOE, 87000 IBR with water.

FCM120 = 120 input, 107 DOE, 93000 IBR.

Maybe the difference is that one of the rooms in the house is a sun room.

18'X13' with average 8.5' ceilings ( it's sloped ).

That room has 170 sq ft of glass which includes 3 skylights each being 32X50, and it has a slab floor ( finished with slate stone ).

And one of the 3 zones in the house is dedicated to that room.

So I think I'm ok.

Any thoughts?

Thanks,

FG.

I understand.

I think it'll do some condensing in the coldest months but not alot.

And I have read that these boilers are more efficient than non-condensing ones even when they aren't condensing.

By your calculations even the smaller unit(s) wouldn't suffice. They would condense just a bit more than the 120.

During the coldest months, the supply water temperature will be higher, meaning the return water temperature will be too high to condense.

Basically, any boiler can be efficient during the coldest period of the year. High-efficiency boilers save fuel during the shoulder seasons. If they are sized correctly, or as close to correctly as possible.

Joe

 

[BrownianHeatingTech]

Well, I went to SlantFin and did the heat loss worksheet.

It came up with total btu's of 78000.

The Slant/Fin program is known for giving very high numbers. It assumes "worst case" on pretty much every calculation.

I can put the same house plan into Uponor's heat loss program, and get dramatically different numbers.

Your length of baseboard puts a solid cap on your heat loss. If your house will heat with 84 linear feet of baseboard, then there is no way your heat loss is 78kbtuh. Just not possible to get that much from that length of baseboard.

You said I'd need some 56000 and that would average 28000. I don't understand that calculation.

It's not a calculation - just a rule of thumb. Average heat loss is almost exactly half of peak heat loss in residences. Close enough for real world use, anyway.

Joe

 

[flamegrabber]

Joe,

Here's another wrinkle:

Of the 84 feet of baseboard ( small fin wrapped around the conduit pipe ), just over 25 feet of it is older.

This part's fins are just over 2" in height x 5.5" wide, each having 3 evenly spaced 0.5" ( looks like 1/2 inch anyway ) pipes through it. One thru the outside, middle and inside. I'm sure you've seen something like this before.

So there are 3 conduits through these older base boards, thru 2"x5" copper fins.

Do I multiply this 25+ feet by 3 because of the 3 conduits?

How, if at all does this change the situation?

Previous = 84' total, single conduit finned baseboard.

Now 59 feet of single finned baseboard as before, and 25+ feet of this triple conduit quite a bit larger finned ( 2"x5.5" ) baseboard.

Thanks,

FG.

Well, I went to SlantFin and did the heat loss worksheet.

It came up with total btu's of 78000.

The Slant/Fin program is known for giving very high numbers. It assumes "worst case" on pretty much every calculation.

I can put the same house plan into Uponor's heat loss program, and get dramatically different numbers.

Your length of baseboard puts a solid cap on your heat loss. If your house will heat with 84 linear feet of baseboard, then there is no way your heat loss is 78kbtuh. Just not possible to get that much from that length of baseboard.

You said I'd need some 56000 and that would average 28000. I don't understand that calculation.

It's not a calculation - just a rule of thumb. Average heat loss is almost exactly half of peak heat loss in residences. Close enough for real world use, anyway.

Joe