Help! Boiler for New Construction

Bob Sweet

Try and work within the btu capacity of the coils your using. Most coils heating capacity starts at about 130* and begins gaining btu's as the supply temp rises. If you can size your pump for a 20* delta T through the coil you'd end up with 110* return temps back to the boiler, putting you well within condensing temps. Even at 150* supply temps your bringing back 130* returns. Thats not even addressing the savings your getting from the modulation of a condensing boiler.


Edit: 20* delta T through the coil is used as a example, you'll need to refer to the air handlers spec to determine what the coils performance is able to attain based on gpm through the coil.

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Boston

Help! Boiler decision for new house.....

Ok, you guys already saved me. P&H contractor was "sizing" boiler last week and was going by the size of the 2 coils in the air handlers, plus the pickup from the raiant garage floor plus "some more" for the super stor. Thanks. I understood enough to explain that the coils in the air handlers are probably not the way to size. He may have understood more than he showed, at any rate he had a guy come out from the "supply house" to size the system. Should I worry about the calcs?

Now, what boiler? Here is his short list, I would really appreciate anyone's advice.
(All natural gas, indirect tank, house is 4300 sq ft on 2 floors, has a walk out basement and walk up attic that will remain unfinished but could be finished in the future. 2 air hanlders and about 1000 sq ft of climate panel for all tile,( forfloor warming.) Garage has tubing 9 inch on center. Isocyanene in roof, fiberglass batts in walls.)


Here are the easy options:

Buderus(upcharge, not significant)

W-M C-I vented through chimney(included in house price)

W-M Gold(assume this is Cast Iron, just power vented?)

W-M Ultra(upcharge, not sure how much)

I would welcome any thoughts. My gut tells me to go with the ultra, but I have no real reason for knowing why.

Thanks a load. Decision day is tomorrow.

Mike T., Swampeast MO

Your gut is leading you in the direction of efficiency, but it takes more than just the boiler to make an efficient system. This will be particularly true with a hydro-air.

The other three boilers are essentially conventional and will use the same system design. The Ultra is different and requires changes in the entire system to best utilize its capabilities.

Regardless, you should insist that returns be fully ducted (e.g. not using joist/stud cavities) and that ALL ductwork be VERY WELL sealed! In my experience such is rare because it "costs more"...

Floyd

> Ok, you guys already saved me. P&H contractor was

> "sizing" boiler last week and was going by the

> size of the 2 coils in the air handlers, plus the

> pickup from the raiant garage floor plus "some

> more" for the super stor. Thanks. I understood

> enough to explain that the coils in the air

> handlers are probably not the way to size. He

> may have understood more than he showed, at any

> rate he had a guy come out from the "supply

> house" to size the system. Should I worry about

> the calcs?

>

> Now, what boiler? Here is his short

> list, I would really appreciate anyone's advice.

> (All natural gas, indirect tank, house is 4300 sq

> ft on 2 floors, has a walk out basement and walk

> up attic that will remain unfinished but could

> be finished in the future. 2 air hanlders and

> about 1000 sq ft of climate panel for all tile,(

> forfloor warming.) Garage has tubing 9 inch on

> center. Isocyanene in roof, fiberglass batts in

> walls.)

>

> Here are the easy

> options:

>

> Buderus(upcharge, not

> significant)

>

> W-M C-I vented through

> chimney(included in house price)

>

> W-M

> Gold(assume this is Cast Iron, just power

> vented?)

>

> W-M Ultra(upcharge, not sure how

> much)

>

> I would welcome any thoughts. My gut

> tells me to go with the ultra, but I have no real

> reason for knowing why.

>

> Thanks a load.

> Decision day is tomorrow.

Floyd

My bet...

is that if you went with the Ultra it is probably oversized and you could put in the next smaller for the same money and have plenty of heat. Make sure they are going to install a mixing valves for the in floor tubing, as the air handlers will require higher temps. than the tubing. Also you don't need "some more" for the indirect, that's hogwash!!!!
Sounds to me like the P&H contractor isn't really up on heat loss... I would NEVER have my supply house size my stuff... I'm the one doing the install, not him, it's MY butt!!! Also, what's his main interest???? Right, to SELL more equipment... that's what gives him his bonus at the end of the year....
As has been said here many times your equipment is only as good as the installation....check out your contractor throughly, many of those that reside here are WAY above average.

Good Luck!!!

Floyd

Boston

I have no choice on the contractor......

I wish I did. That's why I am asking the question.....Thanks for the replies, but I still don't have much to go on....I know it is a system, but its new construction and the only thing we have is 2 air handlers and a gas line from the street. So it can be piped any way it needs to.....

Sounds like I may need to figure out a way to verify the heat loss calculations. I never thought about the supply house probably would prefer to sell a bigger boiler over the smaller one, all else being equal.

Why do you think the ultra could be smaller?

Floyd

Higher eff. for one...

everything helps and the few % higher can make a difference. Also I have found that if the modulation is setup right and you can cut down the cycling, you can also cut down the BTU's needed.
I heat my 500sq. ft. house in upsate PA. with a 155 Ultra that I have limited to about 80,000 BTU. House has no insualtion to speak of, an old bricker, built in the 30's. I can hold high 60's to 70 with that BTU's. No heat loos calc. made would give me those numbers.... That's why I would go with the Mod. boiler and learn all you can about it, you will be able to fine tune it to give you some unbeliveable results.
To bad you have no choice on the contractor, that really stinks, but that is how it often is with new construction. The GC hires them and will get the guy that will give him the best deal so HE can make more $$$$$..

Floyd

Boston

Thanks Floyd...

As far as the contrator goes - both general and P&H, they are not the usual type of GC's - they do first class work and this house is not typical shoddy new construction - it is custom built and we tried to put in the right materials.

I think it is more a case where the p&H contractor "doesn't know what he doesn't know".

I was reading another thread - is there an advantage in using a condensing boiler when you need 180 degrees temp to make the ar handler work properly. My thinking is the air coils don't work well at lower temperatures -it drives down efficiency.

Floyd

It depends....

What supply air temps. are you looking for???? If you want HOT air coming from the AH then you"ll need 180... if you are okay with an air temp. that will heat the house, but may feel a bit cool, then you will gain a ton of eff. and run way lower water temps. At any rate the mod/con will be higher eff. than any CI boiler at any temp.
At today's prices I would go the cool air way and live with it...and, save the money. Too bad you can't go total radiant, and use AH'rs for cooling only, which they are much better at.

Floyd

Unknown

if its new contruction....

Then why have those AH? Why not put in baseboard heat with zonings and have a/c separated? Can't see having hyronic comfort with air units blowing higher than needed temp air...

Boilerpro_5

I worked on a really fine air handler system......

installed in the 1950's that was using the recently rediscovered concept of air turnover. All supply vents are placed high on walls and returns at floor. The ductwork and air handler are designed for high volume continuous circulation of air. The coil runs on full indoor reset and on a typical day delivers air that is tepid at best. Then system is nearly silent in operation, temperatures are very even trough the home and there are no drafts since the air movement is near the ceiling. With a coil sized for 180F water at design, I usually saw about 90F water (not air!) supply temp to the coil to keep the house comfortable on a typical winter day (mid 20's outdoor). I suspect that this ductwork configuration would also work fairly well for A/C to, eliminating the need for another ductwork system for A/C to work efficiently or the installation of Ductless systems or other A/C.
If you must do forced air, this is the only way to do it and recieve quality comfort and efficiency, IMHO.

Boilerpro

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Boston

BOB: Thanks this makes a

lot of sense.

Since we have the air handlers in place, we are going to use them. House is nealry finished.

But I have been convinced the ultra is the way to go - it seems if I put in a mod-con like the ultra, I have the chance to use its features, by seeing "how low I can go" on the water temp through the air handlers. If I go with a normal C-I boiler I am stuck with what it is, and as you stated, no modulation.

Seems like it is worth a little more, expecially since it is not all tha tmuch of a difference given that its new construction.

I want to add one more thing that I havenot seen mentioned - SPACE SAVINGS. If new houses cost close to $200/sq ft to construct, saving 15 sq ft of space - even if it is a basement - has to be worth something.

Boston

I have decided to go with the

Ultra and the W-M indirect. We will use a mixing valve on the tank and run it hot as we can to get maximum capacity(3 kids)


Thanks for the help. I almost made a big mistake.

Also - form another post - I am going to download the slant-fin heat loss program and see if I can get through it quickly to have a "rough comparison" to check the supply house's calc on boiler sizing. Any tips on using it that would help someone going through it for the first time?

Ron Schroeder

Chilton

I like the Ultra, I have couple out there and am real impressed, however a CI boiler with outdoor reset can also accomplish what you are trying to do with airhandlers. What I would say is get the closest boiler BTU rating as to cover your heatloss, if you are going to be oversized no matter what then that ModCon will relly shine.

Dave Yates (PAH)

size matters!

Have your contractor work with the coil mfgr to size them for a 140F water supply temp. The coil gets a bit fatter, but the Ultra will love the condensing return water temps and your bills for heating will be much lower. Your air delivery temps will feel pleasingly warm, not scorchingly hot.

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Ron Schroeder

Doing a heatloss is the best

thing you can for yourself, check double check and check again and then if there is a big difference between yours and the first two you have ammo to fire with and make sure they have good reasoning for what they claim.

Good Luck

Boston

I can't thank you guys enough

I did the hat loss(I made my wife measure the rooms off the plan instead of watching the US Open, she was not amused)

Came out to 98k , including 14k for the garage which will be radiant.

I feel like I am pretty educated and hopefully this will match what the contractor and supply house come up with.


I used 0 and 70 degrees for parameters, I assume that is appropriate for MA.

Thanks again, I think I can get my guys on the right track with this.

I am also going to suggest they visit the Wall, but I don't think they will listen to me - I get the feeling they want to be the experts and I am a stupid homeowner....

I am off to check what size the ultras come in.

So no extra for indirect hot water. Shoudln't I add just a little extra btus?(Just kidding, I read enough posts to know what you all will say)

I beleive you guys.

Floyd

Ultra 105....

will do just fine for you and if you install the plus 40 tank you would have plenty of hot water with out the mixer, but code will probably require it.

Floyd

Boston

floyd....

don't i need around 90k net - when I looked at the ultra 105 it was 81k net. Naturally I am assuming NET is what you would use to compare to actual heat loss. Am I looking at that wrong too?

Floyd

It depends...:-)

My bet is that the heat loss calc that you did has about 1/3 more BTU's built into it then you will need in real life heating. They do that to cover their backsides......soooooooo the 81 K would probably do fine as long as you didn't do deep setback, or the power didn't go off ofr a few days. The 155 will fit well and it will give a bit of reserve for setback or emerg. It is still a ton better than the 310 beasty that apparently was speced., those boys will heat a barn!!!!
You can backoff the heat side later if you want.....another thing you want them to do is to turn off the "boost" feature in the Ultra, so that they will run better with the big AH's and stay in condensing mode longer. With those big AH's you will be running some very low temps. (high eff.) most of the year...

Floyd