Replacing old gas boiler

Users who are viewing this thread

edednon

New Member
Messages
3
Reaction score
0
Points
1
I'd like to replace my old gas boiler. I don't think it's efficient and I'd like to take advantage of a rebate my gas company provides (needs AFUE 94% and higher) . The old boiler has 110,000 input and 88,000 output btu/hr.
I attached some pictures of it.

I'd like to replace it with this one: http://www.homeperfect.com/weil-mcl...ural-gas-wall-mount-gas-boiler-383800001.html

I know I'd be hiring an HVAC contractor to do the installation, however to save some money I'd like to buy the boiler myself online.

What I'd like to know,
-Based on the specs, will the replacement boiler above do the job (the right kind of boiler I should look for)?
-Comparing to the old boiler, what specs/things should I consider?
-On average, how much installation cost am I looking at?

Thank you very much.
 

Attachments

  • DSC01222.JPG
    DSC01222.JPG
    59.5 KB · Views: 1,371
  • DSC01224.JPG
    DSC01224.JPG
    88.6 KB · Views: 438
  • DSC01225.JPG
    DSC01225.JPG
    89.3 KB · Views: 750

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Yes the WM ECO-110 boiler would probably work as a direct swap-out, but it's almost certainly not the "right" boiler, since it's probably at least 2x bigger than you actually need (maybe 3x), and if your heating system is broken into multiple zones, could be many times too big for any individual zone. The ECO-70 (smallest in the lineup) is probably closer to "right-sized", and still more boiler than you probably need to stay warm. Simply replacing what's there with something of identical output isn't the right way to size a boiler and that goes double for modulating condensing boilers such as this. The ECO-110 would be oversized for 19 out of 20 houses in the US, 9 out of 10 in Canada.

Optimizing the boiler for both the load it needs to support and the available radiation needs more information, such as some valid sort of heat load calculation, a better knowledge of the number of zones zoning, radiation amount & type, by zone, etc.. If you have a mid-winter gas bill with the EXACT meter reading dates it covers, and a postal code (so we can look up heating degree day data, and the outside design temp) there's a chance we can narrower it down for you, since that would be enough to place an upper bound on the absolute magnitude of the heating load.

A condensing boiler whose minimum-fire output is more than your radiation can emit at condensing water temperatures is either going to short-cycle itself into an early grave, or operate at less than 90% efficiency. For that reason it's important to know both the maximum load numbers and the amount/type of radiation. For it to have a chance of working really well the minimum-fire output needs to be less than half your peak heat load, and the radiation on your smallest zone needs to be enough that it can emit that much heat into the room at an average water temperature less than 125F.

Heating your domestic hot water with a condensing boiler would also be a worthwhile thing to do. If the gas HW heater peeking in the edge of that picture is older than 6 years old it would be worth considering installing an "indirect" hot water heater operated as a "priority zone" off the boiler.

It's not clear just how much money you can actually save by buying a boiler online, unless you can get it at "scratch & dent" discount or distress-sale prices. You do the opposite of saving money if you end up buying a boiler that is bigger than you need, or one that won't work well with your radiation. But if we can zoom in on the sizing better there may be reasonable alternates.
 

edednon

New Member
Messages
3
Reaction score
0
Points
1
Thank you so much Dana for your response.

I only used this boiler for one full month several years ago. Noticing that it did not give the heat we needed and gas bill skyrocketed (almost $300 that month), I stopped using it. I use portable electric heaters instead.
I cannot find the meter reading for that particular month, even on my online account (it only goes 24 month back). I live in Philadelphia, PA 19145.

Yes the water heater is more than 6 years old, still works fine though (not sure about the efficiency). I surely consider your suggestion.

So based on your explanation, is it safe to say that I need an HVAC contractor to figure it all out since buying the hardware myself won't be a wise thing to do (for obvious reason)?

I thought I'd save by buying the boiler online rather than buying it through a contractor (which may not carry that model) and perhaps save on tax too.

It seems that I have to call a pro to get this done. I was just entertained by the idea of buying the hardware myself and just hire a pro to install it which is apparently not that simple.

Do you know one around Philadelphia that you can recommend?

I very much appreciate your help, Dana. Thank you.
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Not all HVAC contractors have the math/software skills for either doing the heat load calculations OR designing systems around modulating condensing boiler. If you solicit bids, the contractors who do a Manual-J heat load calculation using a standard tool move to the front of the line, but you also need to look at the computer-generated report for inaccuracies.

It's pretty common for contractors (usually well intentioned) to have a thumb on the scale by what they enter. Common examples of that type of input error would be to use something like 78F instead of 68-72 F for an indoor design temp, and 0F for the outside design temp, in a location where the ACCA Manual-J lists the outside design temp as +5F (your actual outside design temp) or something. The 99th percentile outside design temp is warmer than the absolute record cold, and higher than the typical seasonal absolute low, but even if the absolute low is 10F lower than the 99th percentile temperature bin it doesn't mean you should use the absolute low as the design temp.

Other errors of omission or commission might be to under-rate the R-values of what's in the attic/walls/basement, or mischaracterize the windows if they weren't sure what the real values were. And that all adds up to a bias to the high side, which puts you into a potential oversizing condition, which is what you absolutely want to avoid.

It's possible to get a pretty good rough cut using I=B=R methods (a heat load calculation method that predates Manual-J). How big is the house in square feet, how tall are the ceilings, the total number of floors, and the total number of windows. Are the windows clear-glass double-pane, low-E double-pane, single pane + storm windows, single pane without storms? What is the wall construction type, including siding, insulation type & thickness (if any), and how much insulation (thickness and type) is there in the attic? Is the basement insulated at all? The approximate year or decade it was built is...?
 

edednon

New Member
Messages
3
Reaction score
0
Points
1
The house was built in 1925. It's a two stories row house with flat roof. Living area is approx. 1,350 sq ft (excl. basement).

First floor has two front big windows which are clear glass single-pane (which is an enclosed porch with 2 windows and a door separating from living room), 2 smaller back windows that are clear glass double-pane, and 1 small clear glass double-pane on the side. Since it's a row house, most part of the sides of the house share walls with houses next door. Second floor has 1 master bedroom with 3 front clear glass double-pane + storm windows. 1 smaller bedroom in the back with 2 clear glass double-pane + storm windows, 1 small bedroom in the middle with 1 clear glass double pane + storm window, and 1 small bedroom with skylight. Each room of the second floor has radiator but the hallway itself (total 4 radiators which are varies in sizes).

First floor only has 3 radiator (1 in the enclosed porch, 1 in living room, and 1 in dining room. No radiator in the kitchen).
I'd say overall the insulation is fair at best.

Front wall has aluminum siding, back wall and side walls are brick wall.

Basement is not insulated.

First floor ceiling is 8 ft 8 in high. Second floor ceiling is 8 ft 3 in high.

Maybe in the next couple of week I'll have to call someone to do this since winter is coming soon.

I thank you very much for your help in this matter, Dana. Have a nice day.
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
The house was built in 1925. It's a two stories row house with flat roof. Living area is approx. 1,350 sq ft (excl. basement).

First floor has two front big windows which are clear glass single-pane (which is an enclosed porch with 2 windows and a door separating from living room), 2 smaller back windows that are clear glass double-pane, and 1 small clear glass double-pane on the side. Since it's a row house, most part of the sides of the house share walls with houses next door. Second floor has 1 master bedroom with 3 front clear glass double-pane + storm windows. 1 smaller bedroom in the back with 2 clear glass double-pane + storm windows, 1 small bedroom in the middle with 1 clear glass double pane + storm window, and 1 small bedroom with skylight. Each room of the second floor has radiator but the hallway itself (total 4 radiators which are varies in sizes).

First floor only has 3 radiator (1 in the enclosed porch, 1 in living room, and 1 in dining room. No radiator in the kitchen).
I'd say overall the insulation is fair at best.

Front wall has aluminum siding, back wall and side walls are brick wall.

Basement is not insulated.

First floor ceiling is 8 ft 8 in high. Second floor ceiling is 8 ft 3 in high.

Maybe in the next couple of week I'll have to call someone to do this since winter is coming soon.

I thank you very much for your help in this matter, Dana. Have a nice day.

You are correct that only the front & back walls (including the front & back basement walls) & roof of a row house count toward the heat load.

But the wall construction and actual R values matter. Is this 3- wythe brick, with no cavity, 2x4 cavity wall with brick siding, or something else? Is the foundation cinder-block with filled cores, hollow cores, or poured concrete?

The biggest heat loss factor is likely to be your windows. Wood-sashed single-panes + storms have a U-factor of about 0.5 BTU/hr per square foot per degree, which is about the same as clear glass double-panes, which is also about the same as a solid wood exterior door (without a storm door). The temperature difference between a 70F indoors and your +5F 99% outside design temp is 65F, so add up the total square footage (the skylight too), and do the math:

U0.5 x 65F x (square footage)= xxxx BTU/hr.

If you give me the rest of the info we can cook up reasonable U-factors for the walls, basement walls, and ceiling.

By the time you add it all up I'd be truly shocked if your heat load is even 25,000 BTU/hr let alone 88,000 BTU/hr, but it's worth running the exercise anyway, since that, plus your radiation determines the max water temperature requirements out of the boiler, as well as the burner sizing.

Assuming it's all controlled as one zone, measure up the radiators and come up with the square feet of "equivalent direct radiation" using this document as a guide.

If it turns out that the place can be heated with 120-130F water with you radiators it might make more sense to heat ht place with a tank type hot water heater than a boiler. There are trade-offs to the approach, but let's continue running the napkin-math to see what ballpark you are in.

It might also make more sense to heat & cool with ductless mini-split heat pumps (or a mini-ducted variable speed heat pump) depending on where the room-by-room and whole-house numbers fall. The cost can be comparable to, often less than a condensing boiler solution, but it also comes with high efficiency air-conditioning. There are trade offs to that approach too, but it's easier to size the equipment correctly to your probably fairly low loads than with boilers.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks