Updating mechanicals in 100+ year old house

sgb9809

Hello,

I'm new to this form (and new to anything HVAC related) but have already done a lot of reading here and I'm looking for additional advice.

My situation is the following: I live in a 100+ year old rowhouse. There is no insulation in the house that we know of and it was originally heated with coal. At some point the chimney vents were sealed off, a natural gas powered radiant system was put in, and the chimney was lined to be used for mechanicals. It's getting time that we replaced the water heater (proactively due to age) and we have discovered that the chimney system is failing. Due to some complexities in the chimney, the estimated costs to fix are over $5k. So we thought maybe it would be time to upgrade our HVAC system to direct vents and decommission the chimney, but this has seemingly opened up a huge can of worms.

We had a bunch of HVAC contractors come, some suggested switching to combi units, some suggested switching to separate direct vent units, and one suggested repairing the chimney, replacing the water heater and keeping our boiler (21 year old cast iron 85ish% Utica 125kbtu). We have a lot of rust which we know is coming from the chimney liner, but also rust appearing below the boiler. Some have said is the boiler deteriorating, some say that it is normal and it will run for another 20 years… All of them said that the existing boiler was oversized, but none of them wanted to perform any sort of heat loss calculations, and none of them really looked beyond the basement to see what was going on with the rest of the house.

We have no idea who installed the existing radiant system (or really when it was installed) and if they really knew anything about heating design or just thought, here's a window, we should put a radiator under it. In some cases we believe the "original" cast iron radiators were replaced with lower profile units for aesthetic reasons. They are still cast iron but I have no idea if they are equivalent to what the space should have. I doubt any actual heat loss calculations were ever done on the house when the system was first installed. In actual usage there are some areas of the house that are colder and some warmer, but I don't know if this is due to improper sizing or just the laws of physics (heat rises and stairwells act as chimneys).

All of the contractors that have suggested combi units (despite saying that the original system is oversized) want to put in a system nearly twice the size, citing DHW needs and saying that the system will just modulate to compensate. I've read here that this is a big red flag for the longevity of the combi.

It also makes me wonder, can you really size a unit without taking to account the size of all the existing radiators in the system? Even if a heat loss calculation is done, if the radiators were never really sized accordingly, would the results still apply? What should one be asking a HVAC contractor to do in this situation?

Thanks in advance!

Hot_water_fan

1. No reason to use a combi unless you’re short on space. They have too many compromises, tanks are better but bigger.
   
2. You size a boiler to the heat loss of building. Radiation plays no part in it. Use this to size the boiler:

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

3. You size the radiation to the heat loss of each room.
4. Does this home have AC?

Steamhead

@sgb9809 , you need a contractor worthy of the name. Where are you located? We might know someone.

Jamie Hall

To slightly modify what @Hot_water_fan said — he's quite right, but not for steam. Steam would be sized to the radiation — although the radiation should have been/should be sized to the heat loss.

It's not quite clear to me whether your existing system is steam or hot water — people sometimes refer to either as "radiation". I makes a difference… like, a big difference. That some of the contractors are talking combi makes me think hot water — but that they are talking combis at all, not doing any sort of heat loss walk through, and suggesting a unit much bigger than what you have, makes me wonder a little if they know what they are doing at all.

The chimney and flues might — or might not — be a problem. You should really get a qualified chimney sweep in to look at what you really have. Not particularly surprised that there might be rust coming from the chimney — which means the liner or liners might need to be replaced — but a competent chimney sweep can evaluate that.

As the rust around the boiler, it may or may not be a problem. That's a good boiler, and they can last a good deal longer than yours has. On the other hand, if it's leaking (or the system is leaking) it may need replacement. Do you have any idea as to whether it is using any makeup water at all? And if so, any idea how much?

As @Steamhead said, what you really need is a reliable heating person (not necessarily HVAC) — and, as he said, we may know someone…

hot_rod

You mentioned radiant? As in radiant floor heat? If so show a pic of the manifold.

sgb9809

Sorry, I should have been more specific!

1) It's a hot water system.

2) I'm located in Philadelphia.

3) Chimney was inspected by a qualified sweep. The problem is two-fold. The house is complicated because we have an alley between our rowhome and the next that occupies basically 2.5' of width on our first floor, but on the upper floors the house is built over the alley. So the chimney is offset over the alley and runs up the party wall. Second problem is that the portion of the chimney that runs over the alley was hidden by a plastered ceiling, and when we opened up the ceiling to look inside we found out that whoever had done the liner previously had basically removed some of the bricks on the side of the non-vertical portion of the chimney. So the liner is technically exposed, despite being hidden in a wall cavity. The liner is galvanized. The chimney sweep said that if they were to reline the chimney that they would have to pull the existing liner completely out (adding to cost) and even if we had a structural engineer ok the opening in the masonry, they would still have to fix the masonry because they couldn't leave the new liner "exposed" (adding to cost). This is what I mean by can of worms!

4) Regarding makeup water, all that I know is that at some point after we moved in (probably more than 5 years ago) a technician did add some more water to the boiler, but I believe it was attributed to evaporation and I don't remember how much.

5) Yes, we have ductless system for AC.

6) @Hot_water_fan Regarding the heat loss calculation, I did in fact do this calculation based on our heating records. However I read more on another forum which pointed out that this method is ultimately working with averages and that averages have nothing to do with sizing. Also, we don't keep our thermostat constant throughout the day (for example at night we turn it down to 60). So, while it is an interesting exercise, I would rather have a qualified, experienced person size the boiler at this point.

I'd be grateful for any suggestions! We have had 6 contractors out to look at it and basically everyone has done the same thing. I think there is an assumption that what was done before should be repeated instead of actually doing any sort of calculation to verify.

Steamhead

@sgb9809 , try these guys:

https://heatinghelp.com/find-a-contractor/detail/pompetti-heating-and-air-conditioning-inc/

Larry Weingarten

Hi, My job sometimes is to state the obvious 😜 The first thing to do is whatever you can to make the shell of the building work better. Once that's done, size the heating system to the new, lower load. I'd start with a blower door test and looking at the building with an infra red camera. This will show you the big leaks. Seal the air leaks. Now look at insulating things. There may be no point in insulating common walls, if the other side of them is kept warm.

Yours, Larry

Hot_water_fan

The heat loss method takes an annual fuel usage divided by annual heating degree days. As such, it uses the linearity of heat loss to make it all work and it holds up. The issue with a manual J is that it uses much guesswork, so quality is very low unless they spend a lot of time (money) on it which most do not.

That said, it could all be academic - the typical 80,000 btu condensing boiler turns down to 8000 btu so that'll be sufficient and don't waste time with a heat loss. If you go non-condensing, then they need to do the heat loss.

sgb9809

@Larry Weingarten I totally agree about insulation, but most of the old homes here were built this way without insulation. All of the exterior walls are basically plaster on brick or plaster on lathe with a very small gap to the exterior brick, which I guess is insulating in a way. I won't go into the marble window sills (the worst idea ever) which are effective cooling devices in the middle of winter… If we were doing a complete renovation then it would make sense, but reframing and insulating the walls is a bit out of the scope of the project.

Larry Weingarten

Hi @sgb9809 , It does sound like insulation is out for now. Still, the low hanging fruit is air leakage. Using a blower door is best, but one can just use a box fan also. Once you have some slight air pressure, you can use a relatively inexpensive IR camera, like Flir One, and/or incense sticks to track down leaks. Often, taking care of air leaks can do as much as adding insulation to add comfort and reduce the energy bill.

Yours, Larry

RickyJGDE

Just curious, do you use your ductless units for heat at all, and if so, how much of the load have you found they can cover?

TerrS

So I have to say, I am not an expert but did so much reading I could give you ideas. I just replaced my 32 old boiler and did not go combi because I would have froze here in Pittsburgh. I had 8 contractor and like your experience every just wanted to replace with a boiler with the same size.

So a few questions, what type of radiators do you have now, I assume hot water and not steam. I went around my house and added how many feet of baseboard heat I had, then did calculations based on BTUs output. In the winter does your current furnace run hours before the house gets warm? Or fractions of that? What is the normal water temperature in the boiler as it's important. If my water wasn't 180-190 again I froze but I also have slant-fin and only produce about 600btu per ft at 180' water. Is this a 1 zone system or multiple?

Next my 1903 house chimney was falling apart due to all the years of condensing but I bought a 35' SS liner for $700 and paid someone to install which was reasonable. Your current opening in your chimney might have been because it had a bend they couldn't drop the liner straight down thru like mine. But should be fairly early to repair after the new liner is installed if that is what is needed.

Like hot water fan stated, use your current gas bills CFMs and there is a calculation that will get your heat loss close. Again it depends on how many emitters you have and their output BTUs, along with your total SQ footage of your house

GrafHeating

You mentioned that some radiation was low profile and part of some previous remodeling. You also mention uneven heat.

This is an old house and I am guessing the piping was sized and routed for convection circulation.It probably now has a circulator.

This will not help with the question that you asked but may prevent another concern after a new boiler.

Water flows differently in convection and circulator systems. The low profile radiators may be playing games on you. They are not designed for gravity flow and have a bit more resistance

As an experiment try running your circulator 24/7 rather than intermittently with calls for heat. There is a good chance that currently water is going preferentially along the course of least resistance. With the older gravity sized pipes you could, in theory, pass all of the circulators capacity through one radiator.

Convection systems where driven by differences in water density caused by disparate temperatures and were to some extent self balancing as the coldest rooms drew more hot water than hotter rooms. When you add that to the fact that the old coal fired version probably had at least some fire for months at a time, things worked out very differently.

Constant circulation best mimics what your system was designed for. Correctly sizing for your buildings heat loss will also help a lot.

Your radiators will likely run cooler , but the temperature will still be the setpoint and distribution more even.

TAG

Did you replace the water heater already (not clear) ? I'm assuming you have a separate gas fired tank unit ?

First — IMO you want to understand/ figure out why the current system is not heating the house or making you comfortable.

I redid quite a few row homes in my days in center city Philly …. none of mine were end units or had side alleys thankfully because trying to retrofit any outside wall insulation is impossible w/o demo. The best you can do is seal things up … but, I'm sure you have figured that out. The outside walls obviously need more heat.

It really comes down to $$ .. you can always rip things out and replace at great cost. What is the overall savings? My guess is fixing the chimney for $5k is the cheapest .. you are done. Replace the water heater when needed … seeing some rust around the boiler? Is it a dusting or chunks — or is there rust falling from the old flue into and down the boiler …most likely.

Sadly — your experience with contractors is not unusual. Many just don't know or want to spend the time. Did you have any loads done when you did the ductless units?

Typically those homes would have had tall typical standing radiators. When installed back in the coal days — guys putting them in knew what they were doing and I'm sure with it being old and coal it was gravity w/ no pump. ….. having a picture of what you are talking about w/ the radiators would help. Also — 125k BTU is not bad …. few manufacturers made small boilers …. you are lucky it's not 200k. Remember — they are around 85% efficient.

My approach … do no harm and KISS. A combi boiler will save some gas but how much and how long will it last and will you like the tankless hot water operation — IMO the numbers never work. Natural gas is cheap.

My last house was a monster in Chestnut Hill — when I redid the two systems in the late 00's the most cost effective way forward was to replace the two huge boilers with new smaller conventional Buderus flue boilers … I did do an indirect for hot water to save some space. Some contractors did say to go condensing but with the higher cost of the units — the gas savings were not there and the life of a traditional high quality cast boiler is in the 40+ year range ….. my guess you would have replaced the condensing 3 times. Traditional high mass hot water works great with old school high mass boilers.

Geosman

Sorry, but I simply could not review this posting without adding a process I use frequently in my work retrofitting homes with geothermal systems. This takes us back to an earlier post that mentioned Degree Days and fuel usage. With the attached text, you can make calculations on your "Occupied Heat Loss" for the existing structure based on your annual fuel consumption and the local degree day weather data for your winter heating season. If you have any difficulty do not hesitate to email me at: persons.jeff@yahoo.com and I may be able to assist with the data.

How to use the ASHRAE Modified Degree Day Energy Estimating Formula to Calculate Heat Loss.pdf

Geosman

A second posting…if you are changing to a condensing boiler to operate using outdoor reset and constant circulation for enhanced energy savings…I had a comparable situation back in 2011 replacing an old monster of a gravity boiler with 10" flu that was barely 65% efficient at best. I used a 3" polypropylene flex vent line to snake 35 feet down an offset chimney. I needed a bucket truck lift to access that chimney over a slate roof. I used a weighted wire cable to lower down the offset chimney to the basement cleanout as a pull line to feed the 3" flex vent from the roof all the way down to its connection in the basement. It worked like a charm. I then set a stainless-steel cap over the open flue to support the vent terminal fittings.

sgb9809

https://forum.heatinghelp.com/discussion/comment/1809513#Comment_1809513

Hmmm… This is an interesting solution! I'm assuming you could only use this liner with HE boilers? All the installers have talked about relining the chimney so we could use low efficiency units, but if this could be done for a lot less, it would make "fixing" the chimney more attractive. Would you still need to run an intake vent directly out through the wall, or can you run two of these lines down the existing chimney and space them at the termination?

Part of the problem with the direct vented units is where to place the vents, as there are lots of windows to work around. Contractors couldn't agree on the position, one guy said the vent had to be 10' above the ground??? Also none of them really cared what the venting would do to the basement layout, ceiling height, etc.. One wanted to run a PVC vent 25' horizontally blocking two windows on the inside…

In our case the chimney is accessible with a ladder, and since there's an opening in the side of the chimney at the offset already, we might not even need to use your snaking method.

Thanks for this idea!

Garrulous

You can do things yourself to answer some of your questions and solve some problems.

I lived in a 1925 house for 35 years. I was determined to reduce my heating cost.

I had no insulation in the walls and changing this was not feasible. I put loose insulation in the attic.

I read that in older houses, air movement through the house causes most of the heat loss. I put a box fan in a window, blowing out. I closed all doors except the door to the room with the fan. I felt for air movement coming out under the closed doors. I tackled the worst leakers first. The main sewer vent was in a chase whose attic closure had a gap. There was no room to remedy this in the attic due to the slope of the roof. I cut into the wall at the bathroom ceiling to find a 1 1/2" x 24" gap. I placed foam board to block off the chase. Each room needed seals around the sash cord pulleys. The sash windows needed weather stripping, et al.

That cut my winter fuel use in half. And I no longer had a curtain of icicles hanging from the edge of the roof.

Next, I subtracted my monthly summer fuel use from each winter month fuel use. I went to the library to find the newspapers that showed number of degree days for each day of the winter. I matched the degree days with the monthly net fuel use. That gave me fuel use per degree day.

I observed that the house stayed about 5 degrees warmer than average outside temperature with no heat on in the shoulder seasons. From that it was easy to figure how much fuel would be needed on a design day (-30 deg F in my case) to keep the inside at 63 degrees—5 degrees below the 68 deg. actual inside temperature that I wanted.

That came to 50,000 Btu/h net, 60,000 Btu/h gross output (about one-fourth the size of my existing hot water boiler).

I bought a new 50,000 Btu/h (net) boiler and had a builder friend install it. Yes, I should have added a safety factor. Five years later the morning temperature was -32 deg F. The house temperature was a bit below set-point. The boiler kept working solidly until 10 am when it caught up and shut off briefly. I rolled the safety factor dice and won (nothing to be proud of in retrospect).

If you're an observant, careful person—who paid attention in eighth grade math—you can do these things too.

Best of luck!

Geosman

sbg9809 to answer your response…sorry for my delay I've been offline for a few weeks and am back at my laptop getting caught up. All the HE boilers I am familiar with allow for the combustion air to be drawn from the interior of the home provided it is not a laundry room. That eliminates having a second line to draw air from the outside. If you have not already researched the flexible pp vent pipe the attached link was my source back in 2011.

https://duravent.com/product/polypro-flex

Jamie Hall

A few notes. First, before you do anything to a 100+ year home (or any building), decide what you are really trying to do. Are you planning to restore the structure, or are you planning to renovate the structure? Those are two seemingly similar but actually very different projects.

Second, find out what you are really dealing with. Structures built up to about 120 years ago tend to be pretty standard, though the standards have changed (a circa 1900 "2 by 4" really was two inches by four inches, unlike post WW II timber). Older structures may have different framing, and Civil War or earlier structures often have very different framing — and while the materials may look at least similar, they may have different structural properties.

I totally agree on replacing galvanized plumbing. It needs to go. So does lead — on supply pipes. On drains, not so much — but if you can get at it, it should go too. This, however, is easier said than done if you are considering restoration. PEX is your friend — it can be snaked into places which can only be reached with extensive destruction if you are using rigid pipes.

If you are working restoration, period correct plumbing fixtures meeting modern codes are available. Original fixtures may still work — or may not, and repairing them can be sufficiently difficult to make the cost of period correct replacement ones very attractive.

Electrics can be a real problem. First place, it is likely that there aren't enough sockets for modern tastes. Adding new ones, however, can be a real chore — particularly in really old buildings. As noted, knob and tube wiring needs to go. What other upgrades — if any — need to be done, however, depends more on your home insurance people than on safety. In my humble opinion (seconded by some veery good electricians), post WW II wiring, if done with armored cable, is fine. Even some earlier armored cable is fine. If it was installed correctly in the first place, the armor is a legal (and safe) ground, but "correctly" can be a gotcha. Any "modern" plastic — junction boxes, Romex, etc. — can interrupt the ground, so check. Many insurance companies will have a heart attack if they see fuses instead of circuit breakers, however — even if the fuse boxes are guarded to ensure that only the correct fuses are used. This can be problematic, but new circuit breaker equipment will have to be to modern code — which may also mandate replacing much of the old armored cable. Can of worms.

Similarly, there may simply not be enough power coming in. That will mean a new main switchboard and, probably, new cable from the street transformer to the building.

Windows. If you are thinking at all in terms of restoration, do NOT even think of installing modern windows. A good carpenter can make even two hundred year old windows just as draught tight, and good storm windows (particularly the inside type) result in an assembly which is very nearly as draught tight as even the best modern window — and which will last another 200 years, rather than 20 for a modern window.

Foundations. Yes, if there is structural failure you'll need to address that. That is unlikely in field stone foundations, but is — regrettably — not all that uncommon in concrete ones. Water intrusion, however, is a different problem. A water intrusion problem, if it is a problem (it may not be), can't be fixed from the inside. You will need to either learn to live with it — or dig proper drainage trenches around the outside to take the water away. Trying to stop it on the inside either won't work — cracks will appear and you will be back where you started — or if it is significant and you do succeed, the foundation may (probably will) collapse as the water pushes against it.

Interior finishes. Try to avoid drywall or sheetrock if at all possible. Lathe and plaster can still be done, and is far superior.

Insulation. There's another can of worms. Usually attic spaces are not a problem — have at it, but remember that spaces which are outside the insulated envelope must be ventilated. Insulating walls can get… interesting. If the framing is balloon or platform, some of the blown in types can work very well. I can't really recommend foam in place, though, as the pressure from the foaming can damage the interior walls (expensive). Earlier framing… difficult, as you don't know where framing members are located.