Advice needed please…

Skyline

The chances are that I'll end up with the DC20-125 IBC boiler. Below is just my attempt to calculate the heat loss and boiler size requirements.

It is more of an exercise for me and hope, I did it right.

The hardest part of the heat-loss calculation is accurately measuring walls, windows, doors, etc., and estimating their "R"/leakage rates. On a 70 years old house, I only know for certain that I've done on the house; the rest is estimated. here's my heat-loss calculation results, best/worst cases:



Taking @The Steam Whisperer 51, 432 btu/hr boiler input calculation, based on last winter natural gas utilization, the boiler size is:

1. Best case: 82,088 btu/hr
   
2. Worst case: 89,348 btu/hr
   

Since the average winter temperature where I live is 25° F, with indoor being 72° F, the difference in temperature is 47° F. Even the the 80-90K btu/hr boiler is mildly oversized.

In the worst case with 100° F difference in temperature would mean that the outdoor temperature is -28° F, that's cold. That requires 113,373 btu/hr boiler size.

The DC20-125 is also be mildly oversized, did I mention that -28° F is really cold?

Intentionally, I did not account for the DHW in this exercise. I understand that my DHW MPG requirement pretty much will decide the boiler size.

mattmia2

Let's see if we can explain this better.

The burner burns gas which produces a mixture of hot gases. that hot gas mixture is routed through a heat exchanger that transfers he heat from the gases produced in combustion to water. This ware is in a closed system that consists of internal boiler piping and the domestic heat distribution system and emitters.

There is a second heat exchanger, usually a flat plate heat exchanger, that has the closed system water on one side and domestic water on the other side. System water circulates in this heat exchanger to make domestic hot water.

The internal plumbing of the boiler varies somewhat by model and manufacturer but the general scheme is usually there is a builtin pump that circulates within the boiler and the near boiler piping and there is a 3 way valve that diverts that flow either out to the domestic heating system or through the domestic hot water heat exchanger. Usually systems like this must be set up for domestic hot water priority (they only make domestic hot water on a domestic hot water call and suspend domestic space heating until the domestic hot water demand is satisfied). Most systems weather they use an indirect water heater or heat directly with a heat exchanger are set up with DHW priority)

One caution with a combi or tankless water heater is that they won't produce hot water until they valve switches and the boiler fires so there will be a brief period of cold water under some conditions. Many have a small tank that stores a gallon or so of domestic hot water to provide hot water until the unit begins producing hot water. Another approach is the HTP Phoenix which stores a tank of system water to immediately produce hot water or domestic heat.

mattmia2

There is a heating and cooling design temp for your area. It is a little less than the records because the record temp only holds for a couple hours and the mass of the structure can carry it through those periods.

Here is one source but google will give you many more:
https://www.captiveaire.com/catalogcontent/fans/sup_mpu/doc/winter_summer_design_temps_us.pdf

Jamie Hall

The usual setup is for the DHW to have priority. So you lose the heat...

The Steam Whisperer

The 51, 432 btu/hr boiler input was at -10F with 70 F indoor.

The average boiler input for heating at 36F average temperature was only 15, 334 btu/hr

hot_rod

mattmia2 said:

Let's see if we can explain this better.

The burner burns gas which produces a mixture of hot gases. that hot gas mixture is routed through a heat exchanger that transfers he heat from the gases produced in combustion to water. This ware is in a closed system that consists of internal boiler piping and the domestic heat distribution system and emitters.

There is a second heat exchanger, usually a flat plate heat exchanger, that has the closed system water on one side and domestic water on the other side. System water circulates in this heat exchanger to make domestic hot water.

The internal plumbing of the boiler varies somewhat by model and manufacturer but the general scheme is usually there is a builtin pump that circulates within the boiler and the near boiler piping and there is a 3 way valve that diverts that flow either out to the domestic heating system or through the domestic hot water heat exchanger. Usually systems like this must be set up for domestic hot water priority (they only make domestic hot water on a domestic hot water call and suspend domestic space heating until the domestic hot water demand is satisfied). Most systems weather they use an indirect water heater or heat directly with a heat exchanger are set up with DHW priority)

One caution with a combi or tankless water heater is that they won't produce hot water until they valve switches and the boiler fires so there will be a brief period of cold water under some conditions. Many have a small tank that stores a gallon or so of domestic hot water to provide hot water until the unit begins producing hot water. Another approach is the HTP Phoenix which stores a tank of system water to immediately produce hot water or domestic heat.

I think most combis have a position that allows you to keep the boiler hot so there is very little delay for DHW, 10 seconds or less. It does cost more fuel of course.
In my case I pay to run a well pump and also a sewage ejector, so the additional LP cost is balanced against running two pumps and waiting for the boiler to ramp from cold start.

Some mod cons hold less that 1 gallon, low mass design, so even a cold start is probably 45 seconds or less, especially in summer when the boiler is in a warm space.

Skyline

The Steam Whisperer said:

The 51, 432 btu/hr boiler input was at -10F with 70 F indoor.

The average boiler input for heating at 36F average temperature was only 15, 334 btu/hr

Thanks for the correction...

Based on my heat/loss calculation "at -10F with 70 F indoor", that adds around 50K btu/hr to the boiler. If it does, the DC20-125 IBC combi-boiler with 3.x GPM DHW output sounds about right for my house.

Correct?

Oversized? Yes, because the DHW requirements...

Skyline

mattmia2 said:

I think most combis have a position that allows you to keep the boiler hot so there is very little delay for DHW, 10 seconds or less. It does cost more fuel of course.
In my case I pay to run a well pump and also a sewage ejector, so the additional LP cost is balanced against running two pumps and waiting for the boiler to ramp from cold start.

Some mod cons hold less that 1 gallon, low mass design, so even a cold start is probably 45 seconds or less, especially in summer when the boiler is in a warm space.

My bathroom is on the other side of the house. As it is now, there's a delay in getting hot water, especially in the winter. Are you saying, that I'll need to give 45 seconds to the existing delay?

hot_rod

There are other fixes for getting the hot to the fixture faster. There are a number or retro fit DHW systems, if that wait time is too long for you.

Depending which mode you run the combi it could be 5- 45 seconds roughly.
The time from hot at the combi to hot at the faucet depends on the distance it has to travel, temperature around the piping.

Skyline

@hot_rod

I guess the delay won't be known, until the combi-boiler is installed. At which point, indirect water heater can be retro-fitted, if required...

hot_rod

Just know the type of water heater has no effect on the delivery from A to B. Changing to an indirect wouldn’t change the wait time.

Larry Weingarten

Hi, A couple of possible fixes for the wait at the bathroom are demand recirculation, or adding a small 120 volt electric tank as a point-of-use heater. My experience is that as long as the tank has at least three times the volume of water in the hot line, the output of the small tank doesn't cool down so much before it begins filling with heated water, that it becomes a problem. So, put another way, if you need to run one gallon of water from the line before it gets hot, you'll need at least a three gallon tank... not that anybody makes such a beast

Yours, Larry

Skyline

Let me get something straight...

The combi-boiler needs to be oversized, due to the DHW requirements, that has additional delay to get the hot water at the faucet. The wasted water will show up in the water and sewage bill as additional cost. Yes, I pay for the water coming in and going out.

On the top of that, the oversized boiler may not even condensate at times, depending on the turn down ratio, ramp up time, the radiator, baseboards, etc., that effectively reducing its efficiency closer to 85%.

Then there's installation and the yearly maintenance cost during the years that is associated with these type of boilers.

My current Phase III has no issues with the hot water, for that matter with the heat, and it's around 80-85% energy efficient. There's no loss of heat, if the hot water is turned on.

Should I keep looking at the combi-boiler, or get a new "Phase III", or whatever its name nowadays and stay away from the wall mounted combi-boiler?

I'd love to see an ROI on both the "Phase III" and the IBC DC series boilers.

xmorganx

I only scanned through the rest of the conversation, but there is no need to size the boiler to your rads. Size your boiler to the heat loss of your house and adjust the water temp in consequence. We install a lot of IBC; they're all ok, but I quite like the SL series. The other's are more or less a Bosch in a different box. I'm reluctant to install tankless in all but the smallest of condos- admittedly this has a lot to do with consumer habits more than anything else. I prefer to use an indirect, personally.
And no, you cant randomly take the heat source out of your kitchen and expect to be comfortable. Radiant floor, and differently sized or placed rad and lastly a toe-kick heater (only because the fans are so noisy, and they can be difficult to integrate into a low temp system) are all options.

Skyline

The current, tall, cast iron radiator will be replaced by a wall hung unit, that is lower than the current one with more btu output.

Not long ego, plumbers were installing Navien combi-boilers; one of the contractor actually recommended the Navien two years ego. The other contractor also recommends the IBC DC series, but stated that Navien third, or fourth generation boilers are very good.

I have another contractor coming out tomorrow and hope, he does not install IBC boilers. It would be nice to see the other side of the fence...

hot_rod

> @Skyline said:
> Let me get something straight...
>
> The combi-boiler needs to be oversized, due to the DHW requirements, that has additional delay to get the hot water at the faucet. The wasted water will show up in the water and sewage bill as additional cost. Yes, I pay for the water coming in and going out.
>
> On the top of that, the oversized boiler may not even condensate at times, depending on the turn down ratio, ramp up time, the radiator, baseboards, etc., that effectively reducing its efficiency closer to 85%.
>
> Then there's installation and the yearly maintenance cost during the years that is associated with these type of boilers.
>
> My current Phase III has no issues with the hot water, for that matter with the heat, and it's around 80-85% energy efficient. There's no loss of heat, if the hot water is turned on.
>
> Should I keep looking at the combi-boiler, or get a new "Phase III", or whatever its name nowadays and stay away from the wall mounted combi-boiler?
>
> I'd love to see an ROI on both the "Phase III" and the IBC DC series boilers.


Hmmm,
the boiler needs to size to the largest load, period.
In your case for the instantaneous, constant flow you desire you need a 120.
In some applications loads match, in some the heat load is larger.

You have the ability to lock the boiler output to your heat load. If you calculate that to be 40 K, lock the boiler to 40K

There is very little waste if you keep the boiler in DHW maintain mode.

The boiler will condense when return is below 130f, that could be 80% of you heat season. The weather nah building heat loss in charge of that.

The efficiency has nothing to do with Net output, a btu is a btu.

A boiler and indirect will also lock out the heat as it recovers, could be 20 minutes or more.

Other than that 😉

Skyline

hot_rod said:

Hmmm,
the boiler needs to size to the largest load, period.

In your case for the instantaneous, constant flow you desire you need a 120.
In some applications loads match, in some the heat load is larger.
You have the ability to lock the boiler output to your heat load. If you calculate that to be 40 K, lock the boiler to 40K
There is very little waste if you keep the boiler in DHW maintain mode.
The boiler will condense when return is below 130f, that could be 80% of you heat season. The weather nah building heat loss in charge of that.
The efficiency has nothing to do with Net output, a btu is a btu.
A boiler and indirect will also lock out the heat as it recovers, could be 20 minutes or more.

Other than that 😉

I am a OK with the 120K boiler, just not a OK with the DC series boilers at the current time. There might be plenty of others on the market, that are at least as good, if not more, than the IBC boilers.

I'll may just end up with the DC series, but need to explore my options.

mattmia2

The one thing that does vary a lot between modcons is the ability to customize behavior based on your loads. Some have better ways than others to tell them that look the incoming water temp is very low but the outdoor temp is high, don't fire at a high rate trying to get that water up to setpoint, fire at a lower rate for a longer time and things like that. if you really want to choose in detail, look at the installation manuals at those features. Most have some of those features, some work better than others.

Jamie Hall

To add to @mattmia2 's comment -- not only do some work better than others, but there is no standardization among manufacturers (even sometimes different lines for a single manufacturer) as to what the nomenclature is for the various controls, never mind how to make them work. This is one reason for picking a boiler which has known good service support in your area -- the people are more likely to know how to program it.

Skyline

Jamie Hall said:

To add to @mattmia2 's comment -- not only do some work better than others, but there is no standardization among manufacturers (even sometimes different lines for a single manufacturer) as to what the nomenclature is for the various controls, never mind how to make them work. This is one reason for picking a boiler which has known good service support in your area -- the people are more likely to know how to program it.

That could be a double edge sword...

They may likely know how to program it, since there's little options to do that. How would I know, if that's not the case?

Having known good service in the area is not an option, that I've considered yet. Thanks for that...

hot_rod

Manuals and online tutorials can get most folks through the programming of digital devices these days..

The bigger question is knowing why you are programming the control to do certain functions.

Understanding the hydronics and thermodynamics of the system is key to getting the best performance, reliability and efficiency from the system.
Setup varies widely from system to system, depending on your objectives. That is what a seasoned pro brings to the job, knowing the how and why's

It can be a tough go to bring a newbie to pro over the course of several online posts

Skyline

@hot_rod

I don't disagree with you, "newbies" can do more damage, than good when it comes system controls.

On the other hand...

Can I trust the installer, that he/she knows the ins and outs of the system controller?

So far, I've seen four installers and only one did a load assessment, neither did a heat/loss calculation. They recommended boilers between 120 - 160K Btu ratings.

As Billy Joel said...

I could go with the one, who recommended the 120K Btu boiler and cross my finger...

mattmia2

It is both. you need an installer that read and understood the manual but a homeowner that understands what the settings are trying to accomplish and knows the conditions to avoid to prolong the life of the boiler has far more time to observer how the boiler and system react and can tweak the settings to match that particular installation better than an installer ever could.

ratio

& it's even worse that that—you can't even go by how much the installer costs! Although too cheap is a warning sign, expensive isn't a guarantee of skill either.

Best is previous experience, yours or someone you trust; next is a thorough vetting via examination of other installs. We can help with that. Best in a different way is to do it yourself, we can help with that too, but it is costly in other ways.