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Posted by HeatPro on May 17, 2006 at 10:43:02:
In Reply to: Re: Gas Steam Boiler posted by joe on May 17, 2006 at 09:05:41:
Yes, Joe's detail is awesome. It's great to have Joe on the forum.
Part of Steve's question about the boiler is about whether to get a new boiler and then another after the addition is built. Usually the two boilers and others of the type Joe describes modulate- that is - they reduce their fire to meet the demand. This means that you can install a boiler now that will handle the future requirements of your building, yet it will not be too big for the existing building. That does change the estimating in some towns saying that a boiler can't have more input than 5% more than an estimate; but that doesn't apply to these modulating boilers.
One point about selecting baseboard. When you use a water temperature of 180F, most baseboard emits about 600 btuh per linear foot. When you use condensing boilers, it is good to deseign at about 140F water temperature at the hottest. (this is alos a benefit in that the indirect water heater doesn't get such scalding-hot water) This means that the baseboard would put out about 300 btuh per foot, so you need to use TWICE as much baseboard (than when you use 180F) to get the necessary heat into the room.
More often than expected, cast iron radiators are so far larger than needed that the old radiators can heat the home at 140F. I've seen radiators that can heat the whole house under a picture window in a little living room. You can get an idea of how to rate cast radiators for water heat at:
http://64.226.150.132/hydronic/rad/radlook.htm