Adding a hot water zone to 1p steam (Boiler Sizing)

michael_15

I wanted to add heat to the back two rooms of my house (which are unheated, cold, have freezing pipes, and all that good stuff), which currently uses 1-pipe steam. A contractor (who I got from this site and is probably reading this post...) said that it might be considerably cheaper/easier to add hot water baseboards, mostly for the ease of getting the pipes there. (There back rooms have no accessible crawlspace/basement beneath them, so there would be a long (>15ft) horizontal run required from the rest of the house.)

After the initial "Can you do that?" and some consultation in Dan's book which I just got, I suppose you really can do that. I just need to determine if my boiler is big enough to actually handle extra load to begin with. My house has an excess of piping, so rather than just find the EDR of the radiators and then multiply by some factor, I measured the piping and used the BTU radiated from bare cast iron to try to convert the pipes into more square-feet-EDR. I came up with the following:

1) 5 Radiators at 160 sq feet EDR total
2) 66/74/7/30 feet of 1/1.25.1.5/2 inch pipes, respectively. I determined (could be wrong, I was pulling info from various places) that the pipes were 0.513/0.633/0.721/0.883 square feet EDR per foot of pipe.

Adding these up gets to 274 sq feet of total load. I haven't multiplied by any pickup factors.

I don't know how to read the rating on my boiler. It has Input of 105K BTU, "DOE" of 87K BTU, and "Net Steam" of 65K BTU. Dividing the 65K by 240 BTU gets me to ... 271 sq feet of capacity.

All sorts of (not necessarily consistent nor correct) conclusions started rushing through my head:

a) If I add a pickup factor, then this boiler is undersized.
b) Or, since I already counted the pipe, I don't need a pickup factor.
c) Or, the "net" rating on the boiler already considers the pickup factor.
d) If I insulate my pipes, I can reduce their EDR and hence have room for an extra zone.
e) If I insulate my pipes and don't add an extra zone, is my boiler suddenly oversized? From a rough calculation, I concluded that insulated (1" insulation) pipe probably have an effective EDR of 20-25% of bare pipe.
f) I'm almost certainly missing something because I'm considering the heat a hot pipe puts out, but not the energy needed to heat the pipe. . . Perhaps this is why I still need a pickup factor.
g) I haven't a clue how to determine how much load the hot water zone would need. I'm thinking those words like "heat loss" will come into play (though I'm not sure), which means I'd need to hit the books again to figure out what that is...

Anyway, I figured that there would be plenty of smart people here who might be able to offer some advice about my situation. Thanks!

As a tiny extra note, of all that 170-some feet of piping, only 21' of 2" and 27' of 1" pipe lead to a main vent (which is clogged anyway and needs replacing). The rest of the pipes are vented by the radiators. I get a lot of hissing. What size main vent should I replace the current one with? The current one appears to be a ventrite, but is so old I can't tell what type it was to begin with. Thanks again,

-Michael

Steamhead

Start with the boiler size

the 271 square feet/65K Net ratings refer to the connected radiation. This set of ratings includes a pick-up factor of 1.3, which takes care of the piping as long as it's well insulated and not too excessive. I'll bet you have a small Burnham boiler, right?

If you only have 160 square feet of actual radiation, you should have plenty of capacity. How much heat will the addition require?

If you've had trouble with freezing pipes in the addition, you may want to create the needed access and install steam. Steam pipes drain dry when the system is off, so they won't freeze. The long run won't be a problem as long as it's well drained and vented.

Measure the length and diameter of each of your steam mains and the new run to the addition. This will tell us what vents are needed.

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ed wallace

adding hot water zone

i believe i am the person who talked to him about adding hot water zone to his house my idea was to use pex to hook into baseboard in 3 rooms i explained the importance of measureing the radiators to come up with the connected load i also explained the boiler is not piped correctly guess it went over his head

Mark Eatherton1

Ed...

Make sure you use a 3 way tempering valve if you're going to use PEX... I used a TACO on the last one I did.

ME

michael_15

boiler sizing

It is indeed a smaller Burnham boiler.

My "addition" (it's >75 years old, it just happens to be unheated) has three rooms with a bunch of north-facing exterior walls and windows. I did a quick heat loss calc. on it and came up with around 13500 BTU/h. Say, that sounds like a lot. The room with the freezing pipes used to have a stove which doubled as a heater and didn't have pipes freeze; I'm hoping that restoring heat to the room (and adding insulation to the pipes) will remedy that problem.

Since we're currently looking at adding a hot water zone, the steam mains in place are already measured. The main one is 21'x2" and 27'x1" (the dry return) leading up to the main vent. There are two other unvented counterflow mains, both of which are roughly 18'x1.25" (and each lead to a 10'x1.25" riser to the 2nd floor). One of these additional mains tees off horizontally from the header (like a sideways "T"), which, to my understanding, explains why the radiator at the end of it is so darned slow to heat.

michael_15

adding hot water zone

You were indeed the person talking about the hot water zone.

And sure, I understand everything you explained to me about the issues with the boiler piping -- when you spoke to me I hadn't yet gotten my eyes on Dan's book. I'm still paging through it, but what you said makes sense.

You pointed to the height between the horizontal header and the waterline should be 24" (which it isn't; more like 20"), which you called the "A" dimension. I think this may be a misnomer, though I could be wrong. While the waterline-header height is definitely too short, my dry return-waterline height (which as far as I can tell is the "A" dimension) exceeds 28".

The Hartford Loop definitely goes a bit too high. It is basically level with the waterline. The bullhead tee causing slow heating I'm aware of as well.

Another thing which you didn't point out but seems to be amiss is that my equalizer seems to be a bit too dinky at 1.25". Perhaps this is due to my small system size in general.

ed wallace

adding heat

its more important to know what you have connectted to the boiler as a heat load IE: radiator sizes then the pipeing in the basement