Who's right???

andy_21

Getting estimates on a new Direct vent Gas fired cast iron w/ outdoor reset, heating system for 3000sq'2 1/2 bath new construction home.
1ST fl. Radiant w/Hydro air back up, 2 nd fl Hydroair& 60 gal Indirect domestic hot water w/ prority.
Did the slantfin heat loss program & came up w/ 73K @ 0 design.From everything I read here, do the heat loss & size boiler to largest load. The heating contractor & plumber I met with want to go 120-130K. They say you need to account for the Indirect w/ at least 40K btu.
What they way to go?
I've stayed w/ Cast iron type because of the Different temp set up that we have, so I don't think the Mod/Con would help. Any ideas?

Radiant Wizard

Btu for Indirect

You do not have to account for the btu's for the indirect as you should be using a priority control thus making it irrelevant...

ALH_4

thoughts

I would size the boiler for the heat load, unless there is a particularly high domestic hot water load. Short-cycling is a very common problem, and there is no reason to deliberately cause it. Obviously I am completely guessing, but for a typical new home, 24btu/sf is an over-estimate of the heat load. I think you will find that the actual load is less than that, depending on the design of the house. Lots of windows, particularly high ceilings, or lots of rooms with 3 exposed walls among other factors will affect the heat load significantly.

You can size air handlers for reduced temperatures also. It is worth looking at a mod/con, particularly with a direct vent application. The mod/cons have the advantage of being compact, wall-hung, and sealed combustion, even without the efficiency gains, which you can still take partial advantage of with hydro-air.

The Vitodens 200 or 100 would be excellent choices. They do not necessarily need to be connected to a Viessmann indirect. The Triangle Tube Prestige is also a nice choice with a competitive price, though the smallest version is the 110.

Robert O'Brien

Consider

sizing the Hydro coils for a lower temp to allow for condensation for a good portion of the time and go with the Mod/Con.You only pay for the coils once. If you require more DHW than the boiler can recover go with a larger indirect and/or operate indirect at 160 w/ a Tempering valve(which you should have anyway)I'd keep looking for contractors

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Mad Dog_2

All three distinquished colleages are correct

Your "contractors" are playing it safe and not doing the math. Will they be paying your heating bill every month?
A Mod Con should NOT be ruled out. You reallt should get some quotes from the pros here at Find a Professional....The Best in the Business.....MaD dog

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Boilerpro_5

Yes.

> Getting estimates on a new Direct vent Gas fired

> cast iron w/ outdoor reset, heating system for

> 3000sq'2 1/2 bath new construction home. 1ST fl.

> Radiant w/Hydro air back up, 2 nd fl Hydroair&

> 60 gal Indirect domestic hot water w/

> prority. Did the slantfin heat loss program &

> came up w/ 73K @ 0 design.From everything I read

> here, do the heat loss & size boiler to largest

> load. The heating contractor & plumber I met with

> want to go 120-130K. They say you need to account

> for the Indirect w/ at least 40K btu. What they

> way to go? I've stayed w/ Cast iron type because

> of the Different temp set up that we have, so I

> don't think the Mod/Con would help. Any ideas?





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Boilerpro_5

Yes.

> Getting estimates on a new Direct vent Gas fired

> cast iron w/ outdoor reset, heating system for

> 3000sq'2 1/2 bath new construction home. 1ST fl.

> Radiant w/Hydro air back up, 2 nd fl Hydroair&

> 60 gal Indirect domestic hot water w/

> prority. Did the slantfin heat loss program &

> came up w/ 73K @ 0 design.From everything I read

> here, do the heat loss & size boiler to largest

> load. The heating contractor & plumber I met with

> want to go 120-130K. They say you need to account

> for the Indirect w/ at least 40K btu. What they

> way to go? I've stayed w/ Cast iron type because

> of the Different temp set up that we have, so I

> don't think the Mod/Con would help. Any ideas?





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Boilerpro_5

Yes.

What they have said already is quite true. Even your own heat load number seems high. I have a 2,800 sq ft 1906 two story 9 foot ceilings down, 8 ft up, and 700 sq ft of glass and my load is less than 50,000btu/hr at -4F. Oversized, misapplied boilers are hugely wasteful, wear out faster, and reduce comfort. Also, in several areas are against code. The one caveat for your installation is that I would increase the capacity some in order to make up for the typically 20% extra loss due to forced air ductwork.

Boilerpro

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