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JavelinJavelin Member Posts: 100
Heating Help Pros,

We just bought a big old fixer upper from 1911 last year. We were told that the boiler was on it's last leg and sure enough, come March, it breathed it's last breath. I've been shopping around different contractors and have been receiving all sorts of information and all sorts of pricing. Some contractors are quoting a boiler near the size of the old one that's in there (which I believe is WAY oversized), others, are quoting boiler sizes based on the amount of BTUh radiation needed, while still others are doing a flat sq/ft floor measurements and only one did a very rudimentary heat loss calculation.

So, in reading (for hours) all the posts on this forum, I decided to get as much information as possible and ask all of you pros what your thoughts on my current situation and hopefully get some advice on a size for a boiler replacement that makes sense without costing me a fortune (since we're pretty house-poor now :)


- Weil McClain Model EGH-85 - Natural Gas - 350,000 BTU Input - 280,000 BYU Output - Net I.B.R. Output Water - 243.5.

- Basement has no radiators, but original big/think black cast iron pipes (3-4 in") that transition into more modern copper (1.5") near the boiler. I mention this because I didn't count the basement into my heat loss calculation. The supply sides are wrapped in good-old asbestos insulation. We've had some friable stuff removed, the remainder is in ok shape, so we're keeping for now (after all, it IS a great insulator)

- The system has two zones.. one for all of the house, and another for what we call the "Family Room" which was added in 1944 - basically they enclosed a once open exterior porch.

- The house throughout has traditional cast iron radiators in all room EXCEPT for the added family room where there is some sort of Convector? radiators (picture attached).


- Mod/Con boiler with indirect DHW tank (to replace an incredibly inefficient electric one we inherited).

- I'm looking specifically at the Lochinvar Knight line with stainless steel heat exchangers, but have also heard/read good things about the Buderus model GB142 with aluminum heat exchangers.

- I guess I would plan on keeping the same zone layout for now, using just the two circ pumps (no valves). EVENTUALLY, I might pull a 3rd zone and make a 1st floor loop in the basement, so I'd have 1st Floor zone, 2nd & 3rd Floor zone, and Family room zone, but that's WAY down the road - just mention it in case it matters.


Calculated Total Radiation:

- I did a count of all the current radiators and calculated total square feet of radiation. I've attached a PDF of my results. I think it's all pretty accurate, except I found no mention of these odd-ball "convector" radiators in the family room, so on my radiation summary, I used the sq/ft model for the big family room only. - Came up with numbers around 220,500 BTU @ 170deg and 238,000 BTY at 180deg water? Possibly?

Calculated Total Square Footage

- I also counted up square footage of the house room my room with my new nifty laser measuring tool. The HEATED area of the house is attached broken down my room (not including basement or walk-in, unheated attic space from the 3rd floor). Total Square footage method showed 4,306 sq.ft.. Looks like I should use at MOST 42BTU/sq.ft so I'm getting about 180,852 BTU needed from that method.

Calculated Heat Loss

- Using the Slant/Fin mobile too, I did (what I think to be the most accurate heat loss calculation). We've replaced all the windows except for 1 on the 2nd and 3rd floors, and I'm adding insulation where I can to bathrooms we're re-doing and blown-in in the crawl-space above the 3rd floor. I used 180F water temp, 70F Indoor Temp and 14F outdoor temp as my variables, and was conservative if anything... In many instances I put 2 courses of brick instead of the probable 3 that's in there. The total Heat Loss for the house came to 149,000 BTU/HR from the program, but again, that doesn't include the basement as I wasn't sure what to do with that.

So you can see, My methods show ranges from 149,000 BTU through 238,000 BTU, but certainly not the old boiler's output of 280,000.

As I mentioned above, I am looking to integrate an indirect hot water tank into this system too, but my understanding is that doesn't really affect the BTU required to heat the house as there is DHW priority mode which will quickly heat the tank as needed, then the boiler will focus on the house heating.. right?

I just want to be sure that we're paying for the correct size boiler, and want to take advantage of the Mod/Con's "steady" mode rather than have an over-sized boiler short cycling/etc.

Any thoughts would be VERY much appreciated.. We have to bite the bullet before next heating season!




  • zacmobilezacmobile Member Posts: 211
    edited July 2013
    right track

    It looks as though you are on the right track but 42 btu/sqft seems outrageously high to me. Also, I doubt you would require 180F supply temperature, even 170F is really high if you've done any envelope improvements at all. I think it would be worth it for you to have a heat loss calc professionally done, i'm sure someone else on here could turn you onto a local contractor. Then you would have some more concrete numbers so you can proceed to the next step. Where are you located?
  • JavelinJavelin Member Posts: 100
    Heating Loss....

    Thanks Zacmobile, - If I get a professional heat loss (as opposed to my Slant/Fin application) one, would you say the findings of that would be the final say-so in terms of BTU boiler sizing? Is that heat-loss method better than the "radiation" measure or "square foot" measure?

    I'm located in Philadelphia, Pennsylvania - anyone know a good resource?

  • JStarJStar Member Posts: 2,668

    I service your area. Give us a call and we can set up a free estimate, and do a full heat loss.

    - Joe Starosielec
    [email protected]
  • SWEISWEI Member Posts: 7,356
    Systems approach

    How possible are additional envelope improvements?  I'd push hard to get those done before next winter, even if I had to finance part or all of the project.  I might even be willing to be a tad cold this winter if I knew I could get them done next summer.  You're at 34 BTUs per square foot now.   It's far better to size and buy your boiler based on better building performance if at all possible.  A mod/con boiler will really sing with a lower system design temp, and your radiation is oversized so you're almost there.  A bit of digging for derating charts will help -- those convectors are going to fall off far faster than the CI rads will.
  • JavelinJavelin Member Posts: 100

    Thanks SWEI, Since we moved in last summer, we've already replaced about 28 windows from the original 1911 variety with nice new wood/clad double pane, Argon filled variety. The remaining windows are really nice leaded glass which we can't bring ourselves to replace, but will be working on adding storm windows there.

    The house has a crawlspace above the third floor (sort of a small triangular attic) where I can add a ton of insulation (none now) and also has a walk-in attic room off the 3rd floor hallway where I can also add insulation against the "envelope".

    We'll continue weatherstripping doors and the like wherever we can, but I think that might be the bulk of the work we can do as I don't plan on replacing most of the interior walls in any way, and have read some bad things about blown-in cavity insulation.

    Even if I size to how I think the house will be insulated in October, it wouldn't be TOO much right? I mean does a difference of 10,000 BTUs either way matter to much?

    How low can I go with the system temperature? Is that sort of a "lower as much as you can and still fee comfortable" sort of thing?
  • SWEISWEI Member Posts: 7,356
    edited July 2013

    You may have over-estimated some of the losses.  My experience is that heat loss calcs tend to err on the high side, especially with radiant heating systems.  They also fail to account for thermal mass, so a slightly smaller than calculated boiler will work better than a slightly larger than calculated model.

    Joe should be able to set you straight -- I'd give him a call.

    A proper assessment of existing radiation will get you a target system design temp.  I find that a season or two of heating and tweaking allows one to dial in the limits and reset curve to perfection.  Once they are dialed in and if the system is properly balanced, we frequently see indoor temps stay within ~1ºF over an entire heating season -- without a thermostat.
  • HomeOwner1HomeOwner1 Member Posts: 134
    Have you considered a combi?

    We have a Navien Ch-240. It works nicely and if your heat loss comes out within range. It could be an option. It was a budget oriented option for us and help simplify infrastructure a lot, since we needed to redo both the heat and hot water all at once. We also had a grossly oversized boiler prior as well.

    It supplies our large home with 3 full baths hot water and heat just fine.

    We were initially looking at a Weil McClain Mod Con with indirectly initially.

    The guys on this forum were helpful, even though they don't care for my choice in boilers. My wallet does though at 25% the total cost of the mentioned higher end brand alternative.
  • JavelinJavelin Member Posts: 100
    Thought about it...

    Thanks HomeOwner1, I did think about it, but thought that a dedicated hot water tank would make more sense using our demands. I'm sure we could rearrange our lifestyle, but we are looking at a solution that will feed two showers (up 3 floors), dishwasher and Laundry simultaneously.... You're saying it feeds your three baths all together at the same time?

    I guess I'm just a bit gun-shy.. replacing such a big old system with something so new and "little" - I'm probably the perfect case example as why things today are so big and oversized.
  • HomeOwner1HomeOwner1 Member Posts: 134
    Never ran short of hot water yet

    Yes, we have run three full baths at once with full household use. No issues encountered yet.

    We set the hot water to 130 degrees, not the 120 default.

    We have newer shower heads as well, which I am sure are lower flow then the ones of yesteryear.

    As well, high efficiency washer and dishwasher.

    You don't lose hot water with them when there is a lot of demand, just some pressure in very high usage situations.

    The advice I got was to measure your gallons per minute from your items you want to run at the same time, like three showers. Then factor in that you will most likely mix cold in with hot on your shower valve, as a factoring as well. Take those factors along with the worst case 5 gpm at 77 delta T (winter time degree delta heat up) and see if that is acceptable for a worst case scenario. It is fine for us. This was the only unit of its kind that has this type of performance and price that we could locate in our research. If not, the units can be cascaded and joined to work together as an option as well.

    The technology works, and it is very small. Heats up extremely quick and noticed no performance difference between our old hot water heater and this.

    Since it is new and they just seem to have the kinks worked out of it in the last couple of years, the brand reputation is not there yet.

    Food for thought, we spoke to others that have been running them for a year or two so far and no complaints on their end as well.

    Ask around, do the research and make your own mind up though.
  • SWEISWEI Member Posts: 7,356
    77F is not a worst case winter condition

    At 130F output, you are assuming 53F incoming water.  That is a bit warmer than many US locales.
  • JavelinJavelin Member Posts: 100

    Thanks again homeowner! What city are you in? That 77 deg. rise seems like it might be more here in Philadelphia in the winter.
  • HomeOwner1HomeOwner1 Member Posts: 134
    In NJ

    We live in Cherry Hill in the same town as the Navien support center, which was a deciding factor as well. Support is really local to us. I figured if they can't support people in their own town then they don't deserve to be around.

    They have their flows in their technical documentation by delta t temperatures.

    I have no idea what the average worst case winter delta T is by region in the US. I am just a homeowner.

    Does the government publish those facts like they do with design day temperatures with region? We needed that particular number to calculate the Modulation setting on our boiler per our region. The outdoor sensor allows the unit to modulate down loop temps during moderately cold days and not short cycle like the old style boilers do.

    You can give their support a call and ask. I did a bunch of times with questions prior to buying.
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