New boiler system considerations

Dla123

Hi,

I found this forum in my process of educating myself about boiler systems, as I am faced with the decision of replacing my home's current implementation. I bought a house that was built in 1926 and took the chimney out (more for layout purposes and to gain an open concept). The boiler in there now is a Weil McLain cast iron heat exchanger boiler from 1987 that was being vented out of the chimney I took out. So time to replace that.

In speaking with 4 different hvac professionals I feel like I'm back to square one and undecided, mainly on the technology. 3 of the 4 guys are proposing the mod/con route (triangle tube, nti) with the integrated hot water heating and the other is proposing a Weil McLain gv906 + 2 hot water heaters.

I'm leaning toward not doing the modulating boiler and going with the Weil McLain or equivalent 80-85% afue, as the price is better and it seems more consistently reliable.

Anything I put in there will have to be direct vented out the side of the house from the boiler room in the basement.

I'm wondering if any of you professionals can help steer me in the right direction. Here is some more info which may be relevant:

-3800 sqft home.
-still has the original single pane Windows w storm windows.
- heating is about half cast iron radiators and half copper baseboards (I've been told those need to be zoned separately)
-current system has 3 pumps and all hvac guys are proposing replacing all the pumps.

Most important factors to me are:
1) reliability (minimum service calls outside of routine maintenance)
2) price (of initial install but also gas bills)
3) ample hot water (fill a tub while dishwasher or laundry is on Etc)

The mod/con solutions seem like they will cost me about 1.5x the price of the Weil McLain.

Two of the guys proposing the mod cons are telling me installation will take between 3-5 days.

Last question is: is it typical to pay the large majority of the cost for the labor/installation on these boilers? in some cases I'm discovering the labor might be 75% of the overall cost including equipment. Is this typical and if not, what is?

Lastly, I really appreciate any help you guys can offer. Looking forward to making an informed decision and moving on!

Dave

Steamhead

We do NOT discuss pricing on this forum. You did see the line with the yellow background at the top of the page where it says that, right?

SWEI

Without getting into specifics, a boiler is just one component (to be fair, the biggest and most expensive single component) of a system. A properly installed and commissioned replacement job can easily come to triple the cost of a naked boiler. If the job is done right, it's entirely worth that.

nicholas bonham-carter

About the pricing ban, every system will be different, and different parts of the country have different labor rates, so that is why we never speak of pricing.
If you install a cast iron boiler, the new flue will have to extend above the roofline, as the exhaust still has a lot of heat in it.
A mod-con boiler can have the sidewall venting, as the exhaust has had almost all the heat taken out of it for heating. The sidewall vent termination must not be close to any wndows or doors.
When you have a boiler installed by a competent hydronics professional, you are paying for a heat loss to be performed, as well as a design which will choose the smallest boiler possible to provide heat and hot water during the few coldest days of the winter. A good skilled installation will be a thing of beauty in itself. It is a lot more than unpacking the new boiler, and connecting a few pipes.
Ask the contractors to provide some pictures of their installations, and post them here so we may see their level of general competence. Maybe someone else can provide a some links to pictures here of good installations, attractive enough to show the guests after dinner.
Mod-cons are able to adapt the water temperature in the loop to the outside temperature, which provides comfort and economy. You may be surprised by the decrease in fuel use with a new system installation. Temperature setbacks are not part of the economy, as fuel is needed to bring the system back up to normal, so a constant, lower temperature is best.
Cast iron radiators are ideal for maximizing this strategy, whereas baseboards are not, as they have no thermal mass, and will require a different water temperature to be effective.--NBC

Dla123

Guys, really sorry about mentioning pricing. Just removed that. I did not see that warning but will not bring that up again. Thx for the responses so far, reading through them now.

Dla123

Interesting, Nicholas. Thanks for the reply. One thing I took from your post is that baseboards are not all that well-suited for a mod-con. Did I interpret this correctly?

Also, do you know if the gv906+ needs to be vented up above Windows? Does 'direct vent' not mean it can just run the exhaust outside almost horizontally and then not have to run it vertically once it's outside?

nicholas bonham-carter

Download, and have a look at the installation manual for the gv906, and it should have the venting requirements in detail.
You can get a start on this by doing your own heat loss calculations, using the SlantFin free app for tablets. This will also give you recommendations for the particular model of their boiler, and it's BTU ratings.
Baseboards need to run at a higher temperature than radiators to get the same heat output as radiators, unless you have lots of baseboard, or the high output ones.--NBC

Robert O'Brien

Dla123 said:

Interesting, Nicholas. Thanks for the reply. One thing I took from your post is that baseboards are not all that well-suited for a mod-con. Did I interpret this correctly?

Like a lot of things it depends. In this case on the amount of radiation. But to make a blanket statement that condensing boilers don't "work" on baseboard systems is completely incorrect. The opposite is much closer to the truth.
http://forum.oiltechtalk.com/attachments/condensingboilersbaseboard.pdf

Robert O'Brien

What % of winter hours will function with a RWT of 130F? Well over 50% IMHO. The modulation part of the equation has zero advantage? Purely anecdotal, but why do I see a 20% lower therm usage across the board with M/C vs 85% CI? These are almost all convector jobs.

Dla123

So in summary, do you feel I'm better off with the 80-85% setup, or the mod/con stainless steel heat exchanger 95% setup?

Lots of really detailed info here and great information. In summary, what would you pros instal in this house given the information in the OP?

Appreciate all the help so far!

Brewbeer

Dla123 said:

So in summary, do you feel I'm better off with the 80-85% setup, or the mod/con stainless steel heat exchanger 95% setup?



Lots of really detailed info here and great information. In summary, what would you pros instal in this house given the information in the OP?



Appreciate all the help so far!

In order to determine if your system will be able to utilize the condensing function of the mod/con, we need to know some more details, such as the heat loss and the emitter outputs. If you need the radiators to run above 130 degrees for most of the heating season, then the mod/con may not be the best option for you. However, if your emitters can provide adequate heat at lower temperatures, then the benefits the mod/con offer become more important to consider.

Also, just to touch on the comments regarding baseboards and mod/cons not necessarily being suited, it really depends on the output of the baseboards and the building heat loss. I can heat my house when it is 32F outside with 100 degree water. So, there really isn't any blanket rule regarding mod/cons and baseboards.

Brewbeer

130 feet of baseboard and buffer tank.

At supply temps of 100 and above (freezing outside or lower) and 2 of 3 zones running (95 feet baseboard) the mod con (WHN055, 10k on low fire) does not cycle.

gennady

Condensing part contributes 7-9% of efficiency at best if i recall number correctly. Main fuel saving comes from modulation, matching boiler firing rate with heating load. But if you will install CI boiler with mixing valve with outdoor reset actuator like i-series taco valves, TRVs and VFD circulator, your comfort and efficiency will be at the top, not far from modulating condensing boiler with TRVs and VFD circulator. System must operate on constant flow and no zoning and thermostat should be utilized.

Brewbeer

Hatterasguy said:

Down to 10K...........perfect. Yes, with two zones running you can get down there.

The UFT-80 will get to 122F on a single zone (60').

I think the other thing that helps keep my system from cycling is each of the radiators in those two zones receive full SWT from the boiler, that is, zone 1 has three radiators (18', 17', 12') but they are piped in parallel, not one continuous loop. Same with zone 2 (two radiators, 30' and 18'). Higher water temps give off more BTUS per foot of baseboard, so piping the radiators in parallel, in theory, allows for more heat to be given off by the radiators before the water returns to the boiler.

@Hatterasguy, it would be an interesting experiment if you were to break your 60' radiator into 2 or 3 or 4 sections piped in parallel, and then see where the temp stabilizes.

Using the baseboard I installed in my recent project (Heat Trim Plus), when supplied with 130 degree water, a continuous 30 foot length gives off about 9,000 BTUs. A 15 foot length gives off about 5,000 BTUs, and two 15 foot lengths piped in parallel would give off about 10,000 BTUs total. So the parallel piping arrangement gives off 10% more BTUs than the continuous loop, in this example. Of course there are details to take into consideration, but this "in theory" example shows how piping radiators in parallel can deliver more heat than one continuous loop.