Considering boiler replacement

obos

Would appreciate some advice on proactive replacement of my boiler and hot water heater.
I live north of Boston and use natural gas for heat, hot water, cooking, and dryer. My house is 100+ years old and is a single zone of forced water through cast iron radiators (around ~1400sq ft).

Planning to do a water heater proactively this summer (10+ years into 6 year tank), and investigating if the boiler is worth doing as well. Neither are currently "broken".

Boiler is from 1987, a Hydrotherm HC-125c. I've had no particular problems to date, but it looks like it's lived a rough life. Last winter the house was more often cold and I had to tweak my thermostat program, but it was also a cold winter so can't say for sure that's a sign of it failing. I do believe it's the source of a mild gas smell that's always in my basement--had this checked out and plumber claimed these units known for that and nothing to do/worry about.

The dilemma for me is I know we aren't going to be here long term and I used just under 1100 therms last year, so there isn't a lot of cost to save by going efficient. My bigger concerns are about unit failure and safety.

njtommy

All boilers aside it sounds like insulating your house should be in the cards as well.

obos

What can be done for insulation is done. It has cellulose in the attic and all windows are double pane. The walls have no cavity to add insulation to--back plastered.

obos

That's an idea I haven't heard of yet in my research. So that I understand correctly, this is essentially a sidearm water heater setup but using a water heater instead of a boiler as your heating method:


What are the advantages to this type of setup as opposed to a combi-boiler like the Navien NCB?

obos

The water heater is definitely getting done, the boiler I'm still evaluating.
I have some fear about making a potentially short-sighted decision on the water heater and then seeing the boiler go in the next year or two. There are some advantages to replacing the whole system at once in my mind, more options, non-emergency work, one scope and bill for work etc. My feeling on the boiler is there is almost no practical value to putting any money into it (repair) so it avoids the possibility of that as well.
I've looked at a few options so far:

• Replacing water heater with conventional, leave boiler as is, cross fingers. (Obviously the cheap/high-risk solution)
  
• Replacing water heater by retrofitting indirect to existing boiler (suggested by a plumber, not tempting)
  
• Replacing boiler and water heater, going with condensing boiler and indirect heater. (Seems like "best" solution, but pricey)
  
• Replacing boiler and water heater with a combi-unit. (Some worry about reliability and complexity, but costs less)
  
• Replace water heater with condensing unit, add pieces to use for home heat if needed. (As suggested here)
  

I expect the Phoenix option for hot water has lower install cost than say a combi-unit as there is simply less plumbing and pieces involved. The material cost of the unit is however in the same ballpark as a combi-unit. Down the road it's likely to have another day of work/materials to convert to heat, so it may end up costing similar money overall. Thus, I asked about the advantages versus a combi-unit...I probably should have explained my thinking better.

ChrisJ

Are your double pain windows still performing good? I've seen many that are 10-20 years old that are already performing poorly.

Also, can you tell us how much insulation is in the attic? Quantity is very important. I have fiberglass in my attic but unfortunately it's only in parts of the attic and it's only 4 inches thick so it's almost useless.

How about your floors? Are any of them over a cold crawlspace or slab? Are any of your doors drafty?

obos

Thank you for the info, it is an interesting idea. Will be worth getting a quote on. I primarily posted here hoping to find out if I was missing a trick, so this is helpful.

The one other price factor will be the Nat Grid rebates--much more offered for a Combi than for any type of standalone water heater. The tankless water heaters actually get the best rebates (among WH), but tankless is one of my hesitations on a combi unit in the first place.

So one other question: my understanding is the Phoenix you suggested is an example of a "condensing water heater". I've used this term to a couple plumbers and both started talking to me about tankless. Is there a better term?

obos

ChrisJ said:

Are your double pain windows still performing good? I've seen many that are 10-20 years old that are already performing poorly.

Also, can you tell us how much insulation is in the attic? Quantity is very important. I have fiberglass in my attic but unfortunately it's only in parts of the attic and it's only 4 inches thick so it's almost useless.

How about your floors? Are any of them over a cold crawlspace or slab? Are any of your doors drafty?

Not positive on attic insulation depth, but I'd guess it's roughly as deep as floor joists--blown in cellulose. They drilled holes in the attic flooring to do it. So 10-12"? It is the whole attic floor--we had some floor boards up when we had the house re-wired to deactivate all the knob and tube they blew that nice combustible material on top of...
The Mass Save energy auditor I had in suggested the attic insulation could be improved on at this point, but we would need to lose the flooring up there and I would need to do the boiler first, because its output was too far out of spec for them to do the work.

Most of the windows are older, cheap vinyl replacements (15 years?). I think most are holding up OK as far as sealing goes--they aren't good windows, but also probably not bad enough to be worth replacing. There are a few much older Andersen double-panes in the house that are in much better shape, but one is a bay window so that's probably a heat suck.

Edit: I have a full basement, no slab or crawlspace. Unheated.

I did a heat loss calculation, a few numbers are ballparks as I wasn't home to double-check measurements but it should be roughly accurate.

Edit:
Short version if preferable to opening docs:

1st Floor (rough)
Calculations
(Factors found in "Heat Loss Factors" Tab at Bottom)
Multiply x Factor = BTU per Hour
(A) Window and Doors: 160.25 Sq. Ft. 45.5 7291.375
(B) Net Wall: 751.75 Sq. Ft. 17.5 13155.625
(C) Cold Ceiling 0 Sq. Ft. 4.9 0
(D) Infiltration 6448 Cub. Ft. 1.9 12251.2
(E) Cold Floor 806 Sq. Ft. 10.5 8463
and/or 0
(E) Cold Floor 0 Lin. Ft. 0
BTU per hour heat loss at 0o Outside Design Temperature: 41161.2
Conversion Number for other Outside Design Temperature (see Outdoor Design Temp Conversion tab): x 1
Adjusted BTU/hr: 41161.2

2nd Floor (rough)
Calculations
(Factors found in "Heat Loss Factors" Tab at Bottom)
Multiply x Factor = BTU per Hour
(A) Window and Doors: 72 Sq. Ft. 45.5 3276
(B) Net Wall: 744 Sq. Ft. 17.5 13020
(C) Cold Ceiling 620 Sq. Ft. 4.9 3038
(D) Infiltration 4960 Cub. Ft. 1.9 9424
(E) Cold Floor 0 Sq. Ft. 10.5 0
and/or 0
(E) Cold Floor 0 Lin. Ft. 0
BTU per hour heat loss at 0o Outside Design Temperature: 28758
Conversion Number for other Outside Design Temperature (see Outdoor Design Temp Conversion tab): x 1
Adjusted BTU/hr: 28758

Sum of sep floors 69919.2

ChrisJ

70,000 btu loss @ 0F in a 1400sqft house?

My actual loss is 72,000 @ -8F in a 1616sqft 150 year old house with 26 windows, most of which are original and practically no insulation other than the little bit in the attic and some in the livingroom walls.

Are you sure that heatloss is accurate? Even my calculated one was only 66,000 @ 0F.

obos

The heat loss calc reminds me of another matter--boiler sizing The one plumber who actually did get back to me with a quote did not size my radiators or do a heat loss calculation, he based off my existing boiler. By my calculations my present boiler is over sized.

I asked about this (while talking about a Navien) and he stated that was a modulating unit and what I cared about was the GPM at 70 deg rise.

That seems to make sense in context of hot water, but not what I've read about home heating. Can someone explain?

ChrisJ

I'm sure one of the pros will respond, but I'd automatically be against him because that is not the proper way to size a boiler. It's the lazy way.

For hot water most say to size to heatloss so as long as you have enough, or more radiation than you need you're golden. If your heatloss is accurate, you'd want something in the 70,000 - 80,000 output range IMO. Keeping in mind, if you size exact it will run best most of the year but may struggle if you drop below 0F or have doors open a lot on a super cold day (carrying groceries in etc).

obos

ChrisJ said:

70,000 btu loss @ 0F in a 1400sqft house?

My actual loss is 72,000 @ -8F in a 1616sqft 150 year old house with 26 windows, most of which are original and practically no insulation other than the little bit in the attic and some in the livingroom walls.

Are you sure that heatloss is accurate? Even my calculated one was only 66,000 @ 0F.

I expect it's somewhat off (high). I used a floorplan and known measurements from some windows and ballparked the rest, guessing big when in doubt. I can try to redo it but I expect it's roughly accurate.

Could also be the factors in the Excel sheet are off, but probably my ballpark figures.

ChrisJ

obos said:

ChrisJ said:

70,000 btu loss @ 0F in a 1400sqft house?

My actual loss is 72,000 @ -8F in a 1616sqft 150 year old house with 26 windows, most of which are original and practically no insulation other than the little bit in the attic and some in the livingroom walls.

Are you sure that heatloss is accurate? Even my calculated one was only 66,000 @ 0F.

I expect it's somewhat off. I used a floorplan and known measurements from some windows and ballparked the rest. I can try to redo it.

I would redo it and take a lot of time.
If you get a good HVAC guy in you can check his loss calculations against yours and it may help make a decision on what size boiler to get.

obos

I will throw this out there, my current boiler in the winter runs 4-6 times a day for an hour at a time, unless it's real cold. I only shoot for 68F, but if it was accurately sized it would run more frequently, correct?

ChrisJ

obos said:

I will throw this out there, my current boiler in the winter runs 4-6 times a day for an hour at a time, unless it's real cold. I only shoot for 68F, but if it was accurately sized it would run more frequently, correct?

Yep.

Basically, in a perfect world on the coldest days it should run almost continuously. Some guys match them to actually run continuously under those conditions, but like I said, even opening the door a lot will drop your temp and it will never recover from it until it warms up a little outside. If you can tolerate 65F for a day or so, then I would go for that.

If you want 68F no matter what, I'd go a little bigger.

njtommy

I have a Navien NCB 240 in my house. I love it minus a couple things. Waiting for the hot water drives me nuts and watching all the water go down the drain. My sink is close to a 40' run from the boiler. It just takes a minute or two. To get there nice and hot. It's a little noisy when it starts up in high fire you can hear the combustion fan motor, but it quiets down after about 30seconds when it modualates down.

4Johnpipe

@njtommy You may need to due a combustion analysis on the unit (noise issue)...You are really not wasting any more water than before the unit slows down the flow to achieve its delta T or rise from the incoming water...

obos

ChrisJ said:

obos said:

ChrisJ said:

70,000 btu loss @ 0F in a 1400sqft house?

My actual loss is 72,000 @ -8F in a 1616sqft 150 year old house with 26 windows, most of which are original and practically no insulation other than the little bit in the attic and some in the livingroom walls.

Are you sure that heatloss is accurate? Even my calculated one was only 66,000 @ 0F.

I expect it's somewhat off. I used a floorplan and known measurements from some windows and ballparked the rest. I can try to redo it.

I would redo it and take a lot of time.
If you get a good HVAC guy in you can check his loss calculations against yours and it may help make a decision on what size boiler to get.

Re-did it with actual measurements for everything and I learned my floor plan doc is a bit off on the house measurements. House is actually closer to 1450sq ft. I also guessed big on some windows etc.

Still, not a wildly different result , even doing 1 room at a time using those spreadsheets--think they came from US-Boiler.

Total is 64651 heat loss at 0 F. 5000BTU is significant but doesn't really move me to a different class of boiler...

njtommy

@4Johnpipe I looked at it this morning it's in prepurge when combustion fan goes to 100%, but will do a combustion test this weekend to double check all numbers.

SWEI

obos said:

Re-did it with actual measurements for everything and I learned my floor plan doc is a bit off on the house measurements. House is actually closer to 1450sq ft. I also guessed big on some windows etc.

Still, not a wildly different result , even doing 1 room at a time using those spreadsheets--think they came from US-Boiler.

Total is 64651 heat loss at 0 F.

45 BTUs per square foot is almost certainly wrong, unless you can hear the wind whistling through the cracks in your walls.

obos

@Hatterasguy Looking over the internals of the Navien (and I'm guessing similar combi-units), it looks like they have a water heater, heat exchangers and a pump to do both hot water and heat. So would it be fair to say that's more or less the same concept you proposed with the Phoenix Light Duty, except with a tankless heater (and all in one box)?

obos

Hatterasguy said:

The Phoenix is just a water heater. It won't do space heating unless you add an additional HX and properly integrate it.

I offered it to you, as previously explained, because you wanted to replace the water heater now and keep the boiler. It provides the possibility of adding space heating in the future.

If you are going to remove the boiler and procure equipment to provide both heat and hot water, then you most certainly can consider the combi if you understand the limitations.

No, I know the Phoenix is just a water heater. I was referring to the method you mentioned with a water heated doing space heating with a circulator and heat exchanger seems to be pretty much what Navien is doing inside their one box with tankless. They have a water heating mechanism, a pump and heat exchangers provided the space heat and water heat outlets. Obviously it's tankless and all in one box...but same core concept.