Is Condensing a good idea for this app?

Homeowner_3

This is my first time on your web site. I'm installing a hydronic system with infloor heat downstairs, baseboard upstairs and DHW. Does it make sense to invest in a condensating boiler (92%) efficiency vs a good old burnham at 88%. I live in northern michigan so heating season last almost 8 months, my house is about 2700sq ft, estm heat loss is 55,000btu/h at -20degF. To further complicate matters I also have a soapstone heater that puts out about 20,000btu/h avg. I want my hydronic heat to make up the difference. Is there a way to calculate the savings from a condensating vs noncondensating? Finally, if I do need a condensating boiler - any recommendations? I know the Viessman is good but pretty pricey. Thanks.

Constantin

Take a couple more things into account

For instance, what are the fuel prices in your area? You may in fact be better off using oil instead of gas, particularly in a non-condensing application. For comparison's sake, use therms (100,000BTU's). You gas bill will usually feature therms. The heating value of a gallon of oil is equal to 1.4 Therms, so once you know what the long-term oil prices are in MI, divide the per gallon price by 1.4 to get an equivalent price to gas on a per therm scale.

For example, the current price for gas is $1.37 per therm in Boston. Long term contracts can be had for $1.15 per gallon of fuel oil. Assuming equally efficient heating plants, that's a 40% difference. In Boston, the fuel oil price would have to rise to $2 per gallon to be equivalent to todays gas prices (and they usually ramp concurrently).

If you really want to get nitpicky, have a look at the up-front costs of getting either system installed. Time value of money may make a big difference (via a NPV calculation). I'm not there yet, as my contractor has not put forth several system proposals just yet. Furthermore, take care in system design, if the return water temperatures are too high (baseboard) then condensation may not occur and the extra cost for the capability is for naught. That's why condensing systems are usually ideal for in-slab and other radiant systems.

As to whether the 4-6% difference is justifiable economically, that all depends on how much fuel you use per annum. One easy approximation is to use your previous years worth of data or that of neighbors to see how much fuel was used. Then see how much money the efficiency increase will save. For example, in our current apartment, we use about 1250 therms of gas per year (hot water, steam heat, gas stove).

Best Case scenario: Assuming that the boiler consumes most of the gas, the 6% difference equates to about 75 therms or $100 per year. We could save even more if the hot water heater was janked and replaced with an IDWH (instead of sending 50% of the heat up the flue, a boiler will achieve a minimum efficiency of 80%). Assuming a 20-year boiler life (and no time-value of money, inflation, etc.), that's about $2000 in savings from heating savings alone. Naturally, a condensing steam boiler makes no sense whatsoever.

The savings for large homes are commensurately higher but only if condensation can occur.

heretic

Condensing vs. Non

Unfortunately, it will be near impossible to calculate your real savings. AFUE rating is not meaningful for low temp condensing applications. You would need to calculate off a sliding scale based upon input/output temperatures, ambient conditions, and any number of other factors. In fact, AFUE is not particularly meaningful in the real world for conventional boilers either. The more you dig into it, the more frustrated you will become.
Sorry to be so negative on this. Everyone would benefit from a more flexible set of standards here.

Ted_5

I would go condensing

In my house I have low temp radiant in lower level[1,160 sqft] and high temp [dry system] radiant on upper level,[1,220 sqft] DHW [53 gal Viessmann indirect] and a FlatPlate for my garage floor[812 sqft] First 3 yrs I lived there I had a Slant/Fin Concept 21 90,000 BTU. Last fall I replaced it with a Viessmann Vitodens 6-24 81,000 LP. So far I have saved at leased 400 gal of LP. This year it was a colder winter then any of the previous.
Size your baseboard for 150F with 20 DT at -20 and it will always be condensing.
Viessmann may be more money, but you have to look at the whole system and what comes with the boiler. The standard control that comes with the boiler has Outdoor reset for boiler [baseboard] can drive a mixing valve on reset, DHW priority, night set back[5 events, 7 different days for all conected systems] also a built in variable speed pump that will do both baseboard and DHW.
Are you in the U.P.? I hope this helps!

Ted

Ted_5

I would go condensing

In my house I have low temp radiant in lower level[1,160 sqft] and high temp [dry system] radiant on upper level,[1,220 sqft] DHW [53 gal Viessmann indirect] and a FlatPlate for my garage floor[812 sqft] First 3 yrs I lived there I had a Slant/Fin Concept 21 90,000 BTU. Last fall I replaced it with a Viessmann Vitodens 6-24 81,000 LP. So far I have saved at leased 400 gal of LP. This year it was a colder winter then any of the previous.
Size your baseboard for 150F with 20 DT at -20 and it will always be condensing.
Viessmann may be more money, but you have to look at the whole system and what comes with the boiler. The standard control that comes with the boiler has Outdoor reset for boiler [baseboard] can drive a mixing valve on reset, DHW priority, night set back[5 events, 7 different days for all conected systems] also a built in variable speed pump that will do both baseboard and DHW.
Are you in the U.P.? I hope this helps!

Ted

S Ebels

Gary

Where are you at in Michigan? I'm between Cadillac and Houghton Lake and -20* is quite low for this area. If you're anywhere south of the Straits you should be using -2* to -10* depending on the actual location.

If you read up on how systems are designed in Germany, home of the boiler police and VERY tough efficiency standards, your system must be designed to heat the home with low water temps. Maximum is 167* at design and the lower the better. This of course brings you into condensing territory. The simple truth is that the lower you can design your system to run the more efficient it becomes. Why this is not practiced here is a mystery to me. Also highly important in their efficiency equation is
recovering the heat from ventilation air. Their philosophy is to seal the structure, then mechanically control the ventilation while recovering the btu's from the exhausted air. When you realize that ventilation air accounts for alomost half the heat load in a well insulated, tightly sealed house it just makes sense.

Condensing is easily done if you design your system correctly and condensing is always desireable from an efficiency standpoint. You simply size your BB so it will supply the required load at 140* water instead of 180*. This will give you a return temp of 125 or less easily making it into condensing territory. Now combine the 70* return water from your slab and you're probably looking at temps in the 100* range. This is a good thing! A Vitodens running at those temps will hit 94-96% easily. It also ramps up quickly for DHW production with little to no standby loss. Can't say enough good things about that boiler.

Size your boiler and heating capacity, be it in floor or BB and then zone the system so the soapstone heater can take care of its part of the structure. Or, with something like the Vitodens you can simply set back the heating curve so it supplies whatever percentage of heating requirements you want and let the stove do the rest. The Mechanical code here in Michigan states that you must have an automaticly firing appliance capable of heating the whole structure to 70*, three feet off the floor and 2 feet in from an outside wall. Basically what that means to you is that your boiler system has to be able to heat the whole house to that spec or it won't pass. Design it that way and then adjust it down according to your needs.

Yes the Viessmann is a chunk of change. You can't however say it's expensive compared to another product because there is nothing else that compares to it. It's at the head of a class of one. As far as using a boiler that has to run at 140* or higher and then mixing your water temps down......... it doesn't gain you anything. The boiler has to see the low water temp directly in order to attain the highest efficiency it can.

e-mail me if you have more questions

sebels@netonecom.net

Unknown

Condensing VS Conventional

Predicting savings is a slippery slope. Impossible to predict therefore crazy to even try. Some (smart) contractors don't offer fuel savings, even though there are substantial savings in the systems they build. Instead, they offer comfort. Our customers want comfort. Once in a while it even involves saving them some money.

In the case of low mass condensing boilers,, some are of the opinion that they are seldom the better value. Take into consideration the higher initial cost, higher maintenance cost, lower reliability, shorter lifespan, scarcity of skilled installers and more important, skilled maintenance mechanics. Even with the stated 30% savings, it sometimes just doesn’t compute.

We should never go so far as to say cast iron (conventional) is non-efficient and condensing boilers are efficient. Experience tells us that the shoulder heating season is where we can offer most of the savings. On a design day they may equal out. But, the other 95% of the season I'll bank on the lightweight.

Mileage may vary.


To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Unknown

What's Appropriate?

Predicting savings is a slippery slope. Impossible to predict therefore crazy to even try. Some (smart) contractors don't even offer fuel savings, even though there are substantial savings in the systems they build. Instead, they offer comfort. Our customers want to be comfortable. Once in a while it even involves saving them some money. Savings are a by product of a technically correct system.

In the case of low mass condensing boilers,, some are of the opinion that they are seldom the better value. Take into consideration the higher initial cost, higher maintenance cost, lower reliability, shorter lifespan, scarcity of skilled installers and more important, skilled maintenance mechanics. Even with the stated 30% savings, it sometimes just doesn’t compute.

We should never go so far as to say cast iron (conventional) is non-efficient and condensing boilers are efficient. Experience tells us that the shoulder heating season is where we can offer most of the savings. On a design day they may equal out. But, the other 95% of the season I'll bank on the lightweight.

I prefer the Viessmann Vitodens 200. Monitor's MZ is also a fine efficient machine although it is not nearly as sophisticated. Not as much money but, certainly not cheap either.



To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Homeowner_3

Good to hear from someone who's done both boilers. $400 return in one year is more than I expected. that gives the Viessman a 4-5 yr payback. Sound like we both have similar situations. Thanks much.

Homeowner_3

I should have mentioned that this is a remodel and I already own a 500gal LP pig. So I'll be using gas. Appreciate your reply. Thanks.

Homeowner_3

I live outside Boynes Falls - Huffman Lake. Now that you mention it we've probably only saw -20 a few times this winter. However, we had quite a few -10's ... would it make a real difference? I was wondering if a slab thermometer would be better around my soapstone heater rather than a wall thermomter? That way I could set slab temp even if my heater is burning. Regarding capacity I've designed the hydronic heat so I can stay comfortable without the soapstone heater. Thanks for your help.

Floyd_5

Gary,

a condensing boiler can be and is a great investment....
not only will you be more comfortable, but with burning LP, the investment in the higher eff. boiler will pay you back much sooner than you think. The prices have just begun to rise.....
However there are other alternatives to the European condensers.... Weil for one is making the Ultra that is fully condensing, modulating, and will do everything that any other boiler will do.
Check it out at http://www.weil-mclain.com/

Homeowner_3

2nd reply

Hi Constantine,
I was in a hurry when I replied to your feedback. After I reread what you wrote, I was thinking the same thing. If I'm already providing 10-30,000 BTu/h from my firewood heater and I have to heat the boiler water up to temp for DHW and baseboard then how much would I save a year with a condensing boiler if it is not condensing all the time. I figure the Viesmann route will cost an extra $2500-3000. I figure my lp bill will be$1000-1200/yr and I'm only saving 5-10% over cast iron then I think I should keep the cash and put in a cheaper but reliable burnham boiler. But then if fuel costs take off ...

Homeowner_3

What have you heard regarding Munchin? They price out just over half of a Viessman. Service issues? reliabilty? I'm not familiar with Monitor, they have a web site? Thanks

Homeowner_3

Great picture! How long have you had the Weil Mc? What's the warrantee on an aluminuum heat exchrgr? How expensive was your boiler? Thanks

Floyd_5

15 yr limited....

on the HX... go to weil's website, Ultra, then warranty.
or try this http://www.weil-mclain.com/ultra/Weil-McLain Warranties Apr03.pdf

I have installed a number of these boilers and have had no trouble so far...one of them has been running since 9/16/03 nonstop in an Agricultural application. I have had one in my home for a year, will get some numbers on savings soon for the year, but they will not be completely fair due to the fact that I have played extensively with the boiler trying to see what I can and cannot do with it.
Fact is that you can do most anything that your little heart desires and soon there will be a ton more things to play with.
As was stated before, if you design for low water temps. a condensing boiler can be a real saver....
They are not cheap, your contractor will probably be looking for a premium price, and if you can talk a wholesaler into selling you one they will be somewhat less. Price is something that I(we) on the wall hesitate to commit to, as they will vary greatly with areas of the country.
The other thing to consider is that this boiler as with any condenser HAS to be piped correctly!!!!! Don't let just any plumber convince you that he's been piping boilers fer 20 yrs and he don't need no stinkin' education on how to pipe boilers.... to many people have done that and been here looking for advice on how to make the thing work.

Do your homework, which it seems like you are willing to do...
AND like is the case with many things... the person that will install and service the equipment is JUST as important as the quality of the equipment it's self. There is no equipment out there that is any better than the person that can install it properly, set it up properly and service it properly.

Good luck with you endeavor to get your best heating system.

Floyd

S Ebels

I can show you

A Vitodens that we installed in a home in Boyne City if you'd like. It's been in two years.