replace old/oversized richmond gas boiler house w/130mbturadat

Boiling Point

Thanks alot Brad and Andrew, the house is a stand alone not a row. first is a heatloss calculation something a plumbing contractor is going to do before or after an estimate? I've gotten a few estimates, But only one company measured my radiators before the estimate but heat loss? I guess a modulatiing boiler doesn't really calculate sizing on it's own ? yes would love a viessman but 17,000 too rich for my blood, but knight at 10,000 with indirect tanks these are big numbers to me . tankless? Thanks you guys

Boiling Point

replace old/oversized richmond gas boiler house w/130mbtu radat

We live philly in an older stone house 1920 (aprox. 3200 sq ft) with 130mbtu worth radiation (cast iron). Existing boiler 1950 290mbtu richmond gravity sys. with two sets 50'ft of runs steel pipe 2 3/8" o.d. tapering down 1" one big zone gas is killing us $$$. Added cellulose insul to roof and btwn 2nd and 3rd floors and storms. Would like to get high eff boiler with indirect tank (we're not moving 2 kids 4 & 8yrs.) condensing? modulating? alum: dunkirk, weil ultra, munchkin vrs. copper or stainless knight and others? tanks?
it gets confusing and expensive

Brad White

Start Here

Calculate a heat loss with your best knowledge of what is insulated, where and how much. (Click on the "Heat Loss Calcs" tab above or find a friendly local heating engineer.)

Without that, you have no target, no bearings.

May I surmise that you have hot water and not steam? I will presume hot water.

Second order of business is to understand that there is absolutely no point in having more boiler than you have radiator to distribute that heat. You are practically 3:1 and that alone is a huge efficiency hit.

Your 130 MBH seems reasonable for 3200 SF, a tad over 40 BTUH per SF. Maybe with insulation that incidental number could be down to 30. Calculate of course then cross-check. My point here is, your radiation can run at a lower temperature allowing greater savings still.

I think a modulating condensing boiler would be ideal if you can work out the venting. I picture Phila. row houses with limited clearances for venting, but it has been done. Up the chimney using it as a chase for example but within a specific listed vent system.

Personally, I would stay away from aluminum heat exchanger boilers. The water-side water treatment folks say to keep the water pH above 8.0 but no one has convinced me that the combustion side, heated and producing pH 4 level condensate is somehow not a problem. Just my opinion absent better information. Stick with stainless steel, 316L or the 400 (430) series. Triangle Tube Prestige is made in NJ along with everything else. Viessmann Vitodens is my default standard, more cost but worth it. The TT prestige gets my second vote but the Knight is up there too with less experience on my side. Everyone has a preference but it gets down to who will service you after the sale?

You are in an excellent position to save some fuel. Hard not to, in fact.

p.s.: Since when is a 1920's house in Philadelphia considered "older"? Did Ben Franklin sleep or fool around there? I did not think so!

ALH_4

Starting point

I cannot add much to what Brad said other than to second his opinion. The starting point is always a heat loss calculation. Then you can determine the fluid temperature necessary to heat the room based on your radiator sizing. Even if this is not a temperature traditionally considered "condensing", which is based on protecting cast iron boilers from deterioration, a mod/con boiler is the only logical choice. We have a few Knights specified, but have not seen them go in yet. I have, however worked extensively with the Viessmann Vitodens. The Vitodens 200 paired with a stainless indirect would be an excellent choice. The larger Vitodens 100 might be a bit small for your application, but check the heat loss before ruling it out if budget is a major concern.

Brad White

Who does it right? You Can!

Seriously, check the link above and take the heat loss yourself as far as you can. You will be adept in a very short time.


Properly, a qualified heating contractor would do it but unless you (or we know that person, we cannot say for sure if your interests would best be served.

For example (and this is not a slam at anyone), there is an "old school" pattern of either:

a) Matching the nameplate rating of the boiler that is there ("It worked before!") or

b) Taking off the radiation and calling that the heat loss. or

c) Using the "door method" ("If it fits through the door it must be the right size.") or

d) The "square foot method" or "raw experience method", taking an assumed floor area multiplied by an experiential factor and calling that the heat loss.

No contractor wants a "call back" for inadequate heat, but over-sizing has a penalty that you the customer pays for the life of the system. You are paying it now.

With the possible exception of "d" none of these will take into account improvements you have made to walls, roofs and windows, sealing of cracks and general betterments made since the boiler was last replaced. How else can you capture those savings? You cannot. Even method "d" is a guess and is really a benchmark factor to compare relative heating requirements for various buildings.

Now, let's also get practical with the professional contractors' time: They may well give you a ballpark number going in (and the number of available boiler increments may well be spot-on using their experience) but their time also has value. They may well follow up with a detailed heat loss once they have the job. You should expect to pay for the service going in or having it built into the price of the job.

They do not have time to do free heat losses only to have their work shopped out to other contractors. It is right and fitting to pay for good work. A heating engineer can also do this reasonably for a fee and is independent. You can also always post the results on this site- some of us may render an opinion. Some may render several!

Using radiators as heat loss: For hot water, this is not the way. For steam, yes, steam boilers have to support the connected radiation. With hot water heating is still good to know what your radiation output is, though! It helps tell you what the highest water temperature you will need on the coldest day.

Modulating indeed is a feature that trims your boiler to the actual demand- this is good! But, you have to start with the right size first. No point in going to a 160 MBH input boiler when a 125 will do it. You want your modulating range to be as wide as possible and not waste it by having it modulate to 60 percent on the coldest day of the year and cycle on-off when it is only 30 degrees out. No sir. You want your boiler to run flat out on the coldest day and modulate down so that it still runs constantly (albeit much lower input) to the warmest outdoor temperature that you can.

Does that make sense?

Brad

Boiling Point

fixing the blues, starting off right

Brad
thanks alot again
i'll check out the heatloss calc above, slant fin and do a bit on my own
and I'll ask the contractor to do one first for proper sizing
thank you
ps if a high eff boiler is made to be multi zoned and is ideally suited for low temp 120 and less why couldn't it supply domestic hot water with either a heat exchanger or individually zoned (sort of instantaneous/ tankless) and instead of indirect?

ALH_4

Combi's

Some smaller boilers offer a flatplate HX installed internally. The largest model I know of is approx 80MBH, or a little over 2 gallons of domestic hot water per minute.

Turning the hot water off and on can produce slugs of cool water from your hot water tap with instantaneous DHW heaters. Plus then you are limited to the DHW flow rate that your boiler, which is properly sized for space heating not DHW, can provide.

I recommend an indirect water heater as the best option for domestic water heating. It takes some space, but it avoids the problems inherent to instantaneous heaters.

Condensing boilers can still condense above 120°F, as the attached diagram shows.

Brad White

You can

heat your domestic water via an indirect and this is commonly recommended. Your system would be set up for "Domestic HW priority" which means that the boiler goes there first, then heats the house. Usually, 100% of the boiler capacity goes to making DHW so the interruption time in heating is short. The boiler temperature boosts for that period of time.

Nothing to prevent you from using an independent domestic HW source. If your DHW load is small (I doubt it) certain Combi models can handle both, almost instantaneous DHW production. Not recommended except for in-law apartments and the occasional weekend home.

Zoning with Mod-Con boilers is not often recommended because micro-loading interferes with best performance. It reduces the load which could lead to cycling at colder outdoor temperatures than otherwise. Putting TRV's (thermostatic radiator valves) on your radiators is favored to allow cruising while providing high limit overheating protection in those rooms.