multi-zones effect on sizing a boiler

[beenthere]

0 with a 10 MPH wind.

[hydronicsman]

Ah, but here's the catch..what are you doing for hot water Mark?

[stopro1]

give you an exact heat loss on your home without knowing anything about it's age, construction, r-values, u-factors etc..
Ashrae winter design temp for Philly is 14. Personally, I would design for a 70 indoor temp at 0 outside with a 15 mph wind.
I can tell you that 60k sounds a little low unless home was built with newer style construction, r19 ext insul and decent windows (better windows if they are large)or upgrade a great deal if an older home. Heat loss programs are JIJO, so don't make too many over assumptions when inputting info. A good rule of thumb that I have use successfully is this:

well insulated, modern home- 18-25 btu's/sq ft
avg to poorly insulated- 25-35 btu's/sq ft
poorly to not insulated- 35-45 btu's/sq ft
barn- 45-60 btu's/sq ft

your home at 60k rings out to 25/ft based on your info. remember the net output of the boiler needs to meet or slightly exceed the heat loss, not the input

curious about the answer to another post- does this boiler need to make domestic hot water such as with tankless coil?

[mark115]

I have a stand alone gas-fired hot water heater. My gas bills in the summer almost go to zero. I have no plans to use an indirect fired hot water heater.

[mark115]

I thought 60K was low, too, but that wasn't the first pass. I had to scale-back on some of my facts. I believe that I made very few assumptions. For example:

house was built in 1955.
I know there's R-11 in the walls and attic. Nothing in the crawl space.
The 2 new rooms that I just added: R-15 in the walls; R-30 in floors and ceilings.

Recently replaced all windows with double-pane, argon filled vinyl.
Re-sided the entire house with R-4 foam under vinyl.

I used 13 degrees outdoor temp, 68 degrees indoor.
The only assumption I made was "infiltration". I had no idea what to use, so I used "average".

!!!CORRECTION!!! The second program I used makes infiltration very easy. So, again, I believe that I made very few assumptions.


[Edited by mark115 on 03-10-2005 at 08:52 PM]

[stopro1]

ok, sounds like you've made some improvements to the house. not telling you 60k is not enough- I assumed your house was built in the 50's or earlier by the boiler age and have never seen exterior wall insul in a house that was built then ,unless it was gutted later and added. good luck

[mark115]

I've decided on a boiler: 103 MBTUH input. And, I like the idea of an outdoor reset. Let's just leave that alone for a little while. Of course, if there are any major objections, please reply.

Now, onto circulators. Several people have recommended 1 circ per zone. Sounds like a good idea. What exactly is "head-feet"?

Dof3 suggested, "If you are planning on replacing the boiler, why don't you use a P/S piping system. Then put a mixing valve in the zones that are too hot."

I'm not exactly sure what is meant by a Preliminary/Secondary system. Is that the same as what someone described to me as a "two-pipe system", where there is 1 loop for each zone, and the radiators are Teed-off of it?