RePlumbing old hot water system for efficiency

Shluffer · Aug 17, 2008

I have a 4K ft^2 house in connecticut. I am concidering what I can do for efficiency. One thaught I had is to replumb the heating lines. I currently have one inch pipes in the basement, with supply lines running up to each radiator on tht three floors. I'm thinking that If I replace it with a half inch home run pex type system, I will decrease the amount of water in the system, and be able to increase the number of zones (one for the third floor, one for the second, and one for the first). Additionaly, I will be able to shut off rooms that we don't comonly use, and only run the rooms we do commonly use at the times we use them. A couple of questions about this;

1) is it worth it? I'm not sure how much more eficient such a system would be. I figure I can get the tubing and manifolds for under 600. A 10% increase in efficiecy would save me about 60 gallons of oil, which would be a three or four year return period.

2) will a half inch pex line provide enough water to heat up an old radiator?

If I go with this, there will be a bunch of complications such as where to put a thermosat on the second floor (its a bunch of bedrooms of a main hall, with no heat in the main hall), and how to run the lines up to the second and third floor radiators. I will also be working on this into the winter, so I will have to come up with a modular way to do it.

Thanks for the help

Southern Man · Aug 17, 2008

If you make revisions to a hydronic supply system without knowing a lot about the system then the chances are very good that you won't like the result. Replacing large pipes with small ones isn't going to save you on fuel, since the larger pipe, even if oversized and uninsulated, will simply act as a mini-radiator and heat the portion of the house that it is running through.

You are much better off putting your money into:
1. Insulation
2. Weather stripping and caulking
3. Tune-ups or replacements to your burner; replace the boiler with a more energy efficient one.

Sponsor · 2022-01-29T12:20:58-0800

Jadnashua · Aug 17, 2008

There are thermostatic valves you can install on each radiator. Assuming the way your system is setup and allows individual radiators to be shut off. This will also help to even out each area automatically.

Shluffer · Aug 17, 2008

My thought on smaller pipes helping would be that less water should take less energy to heat.

I looked into replacing the burner. Unfortunately, the company that makes the boiler I have does not offer replacement burners. Replacing the boiler would cost me 2,500 plus installation. I have a friend who installs the things and would help me, but I still have to find a way to get the new one into my basement. Not sure how I would manage that. Also It would take way to long to pay itself off.

Bill Arden · Aug 18, 2008

Heating more water is not a problem as that water will heat the house eventually. In other words... don't worry about it.

I would look at insulation, air leaks first and THEN look into more efficient radiators since the lower the water temperature the more efficient the boiler will run.

One really nice thing about hydronic heating is it's modularity in that you can add on in floor heating and even add on a ground source heat pump.

NHmaster · Aug 18, 2008

Bill Arden said:
Heating more water is not a problem as that water will heat the house eventually. In other words... don't worry about it.

I would look at insulation, air leaks first and THEN look into more efficient radiators since the lower the water temperature the more efficient the boiler will run.

? Splain this to me Lucy?

Shluffer · Aug 18, 2008

We replaced our windows last summer. It made a significant difference. Is there an "easy" way to find air leeks? Its a big house. the candle / incense trick would take days. I heard at some point that there are inexpensive thermal imagers available. Anyone know where I can find one? I wouldn't be against renting.

Bill Arden · Aug 18, 2008

nhmaster said:
Bill Arden said:

Heating more water is not a problem as that water will heat the house eventually. In other words... don't worry about it.

I would look at insulation, air leaks first and THEN look into more efficient radiators since the lower the water temperature the more efficient the boiler will run.

Click to expand...

? Splain this to me Lucy?

Assuming that the Fire is burning 100% of the fuel, the heat has to go someplace. It will either go up the chimney or go into the house.

The hotter the water, the hotter the exhaust gases going up the chimney are.
Since the heat lost is a product of both the flow rate and the temperature, the amount of total heat lost increases with temperature.

You can see this effect in the info for modulating boilers. The efficiency goes down if you don't have enough radiators to keep the water temperature down.

Jadnashua · Aug 18, 2008

Find a company (your utility company may do it for free) that has a blower door and can find the leaks for you. You could try to do this yourself with several big box fans blowing air into the house. You need to close all of the windows and seal around the fans (maybe tape and heavy plastic). Then go around with a smoke pen to see where it's leaking out.

A thermal imaging camera probably wouldn't work that well in the summer. They work really well in the winter because the temperature differential is greater. The expensive ones can detect minor temperature variations (some as little as a few hundreths of a degree), but they cost big bucks. I played with one once that could detect where a hand was placed on a wall after about 5-minutes. My hand was only there for a few seconds. It was clear as day. That one cost about 100K, though.

Shluffer · Aug 19, 2008

My utility company is only interested if I burn gas for heat. I don't. I wouldn't mind waiting untill the winter to look for the air leaks. The issue is that the thermal imagers I'm seeing cost in the 5K + range. Are there any less accurate ones that are inexpensive?

Redwood · Aug 19, 2008

Sometimes due to the cost of equipment it is better to pay someone to do it rather than invest in expensive equipment to do a one time job.

NHmaster · Aug 19, 2008

Bill Arden said:
Assuming that the Fire is burning 100% of the fuel, the heat has to go someplace. It will either go up the chimney or go into the house.
The hotter the water, the hotter the exhaust gases going up the chimney are.
Since the heat lost is a product of both the flow rate and the temperature, the amount of total heat lost increases with temperature.

You can see this effect in the info for modulating boilers. The efficiency goes down if you don't have enough radiators to keep the water temperature down.

I started to respond to this but realized that it would take about 3 pages to explain why almost everything in this post is wrong. Try www.heatinghelp.com There was a very good explanation posted a few months back by John Siegenthaler on this subject. I'm not slamming you here or anything like that, it's just that you have made some assumptions that on the face of it seem valid but the actual physics are quite different.

Southern Man · Aug 20, 2008

shluffer said:
.....
I looked into replacing the burner. Unfortunately, the company that makes the boiler I have does not offer replacement burners. Replacing the boiler would cost me 2,500 plus installation. I have a friend who installs the things and would help me, but I still have to find a way to get the new one into my basement. Not sure how I would manage that. Also It would take way to long to pay itself off.

You should have a good, reliable technician to keep the burner and boiler cleaned and tuned up. Or you can find the maintenance manual for the boiler, buy the right size brushes and a shop vac, and DIY. A dirty boiler can really cost you in reduced efficiency. Keeping the burner cleaned and tuned is a bit more of a technical job but some tackle it themselves.

You can also lower the temperature of the boiler water at the aquastat. This is very easy to do and similar to a domestic hot water tank setting. Set it as low as possible while still maintaining your house temperature during the coldest day. You can even reset it to a lower temperature when its not as cold. Some of the fancier systems do that automatically.

Also, if the burner only runs intermittently during your coldest days of the winter, time how long the cycles on-off are and give that information to the technician. He/ she can possibly put in a smaller burner nozzle, making the boiler run longer cycles, which are more efficient.

$2500 is not too bad a deal if your boiler is old. The increased efficiency of a new boiler may pay for itself in a shorter period than you think.

Southern Man · Aug 20, 2008

shluffer said:
My utility company is only interested if I burn gas for heat. I don't. I wouldn't mind waiting untill the winter to look for the air leaks. The issue is that the thermal imagers I'm seeing cost in the 5K + range. Are there any less accurate ones that are inexpensive?

They likely will be willing to give you a proposal on a new gas boiler to replace your existing oil boiler. It should tell you how much it would cost to heat your house with their fuel. You could then calculate a pay-back based on your old oil bills.

You can buy an inexpensive â€œspotâ€ thermal scanner by Raytech for about $75. Google â€œraytech minitempâ€. The model with the laser pointer is better than without since it shows you where the center of the scan circle is. This allows you to take rapid temperature readings from several feet away on nearly any surface. On a cold day you can go around the inside of the house and scan for cold spots on walls, ceilings, floors and around windows and get a pretty good idea where your heat is going.

Bill Arden · Aug 20, 2008

nhmaster said:
I started to respond to this but realized that it would take about 3 pages to explain why almost everything in this post is wrong. Try www.heatinghelp.com There was a very good explanation posted a few months back by John Siegenthaler on this subject. I'm not slamming you here or anything like that, it's just that you have made some assumptions that on the face of it seem valid but the actual physics are quite different.

I was unable to find a forum, or any articles on that site from a John Siegenthaler

Like I said, my main assumption is that 100% of the fuel is burned. Some boilers don't have a hot enough fire box temperature.

The most efficient set up would pre-heat the fresh air using the exhaust air, but that would cause problems with soot and frost buildup.

The efficiency of the system can be improved by increasing the heat transfer from the exhaust air to the water by slowing down the rate of exhaust air or by lowering the water temperature.

NHmaster · Aug 21, 2008

Alright, I guess I'll try to tackle this myself.

First off, even the very best of boilers and furnaces do not burn 100% of the fuel input. Some are better than others but nothing burns at 100%

Low water temps at the radiation mean a lower delta T which is the difference between the room temperature and the temperature at the radiation. Hotter radiation gives up more heat, faster. Low water temperatures and constant circulation will heat the envelope but the electrical cost of a constantly running circulator has to be deducted from the "system efficiency" The most efficient would be to take fairly hot water, 160 degrees or better and extract as much of the latent temperature from that water as possible. There is a balance between the outlet temperature, the return temperature and the btu required to heat the envelope.

3/4" copper fin tube @ 4gpm. Water temp 130 f. = 250 btu. @ 180 f. = 590btu.

At lower flow rates ( 1 gpm.) output drops 10 degrees.

Southern Man · Aug 22, 2008

Most circulators are something like 1/25 HP and in most closed loops probably don't use that much so the cost to run them is pretty small compared to the $4/ gallon fuel that a burner uses.

Lower the boiler water temperature and you've got a larger delta T where it really counts: fuel burned vs heat gathered. Sure the lower temperature means the radiators will transfer the heat into the house slower (thus circulators run longer) but unless you've got a real cold day and they can't keep the house warm that shouldn't matter.

I think a good strategy is to set the boiler aquastat as low as it will go, and if you need to bump it up during cold days then do it, up to the maximum (see below). If the house stays warm at the maximum then time the burn cycles and replace the burner nozzle accordingly. Maximum efficiency should be with the burner running near constant with the smallest nozzle possible.

I'd like y'all opinions on what the maximum boiler temperature should be. Mine has a default tab at I think 200 and there is a red triangle on the gauge at 220, when the T&P valve blows off. So my guess is 200.

Bill Arden · Aug 23, 2008

to nhmaster
I think what you are trying to say is that lowering the water temperature will lower the fire box temperature and that will lower the percentage burned.

But most newer boilers isolate the burner fire box area from the boiler so that the fire can reach high enough temps.

Like Southern Man said. lowering the water temperature too far is not good either since you won't be able to keep the building warm.

Southern Man said:
You are much better off putting your money into:
1. Insulation
2. Weather stripping and caulking

Back on the main issue...

I did a blower door test myself of sorts by removing the top of the plenum (mine is in the attic) closing off the vents and turning on the furnace fan.

This caused air to flow into the building and helped me find where air was leaking in.

FYI: I also tested the ductwork itself and found a lot of major leaks.

Bob NH · Aug 24, 2008

As long as the pipes to the radiators are within the area that is normally kept above ambient temperature during the heating season, the heat they lose heats the house and you will save nothing by making the pipes smaller.

If the pipes are running through a crawl space that you don't want to heat, then they should be well insulated and there may be a small advantage to smaller pipes. However, it is almost certain to mess up the circulation system and you may find yourself with inadequate heat on cold days. That would especially be the case if any of your distribution system uses parallel circulation (monoflow tees or multiple zones on at the same time).

I found that the biggest waste in my circulation system was uninsulated pipes under the basement floor that were installed to connect baseboard convectors when oil was $0.14 per gallon in 1965. I have abandoned those pipes.

BigLou · Aug 24, 2008

Bill Arden said:
Like Southern Man said. lowering the water temperature too far is not good either since you won't be able to keep the building warm.

Or worse yet you will get a lot of condensation in both the firebox and the chimney. Any time the exhaust drops below 140 you get condensation. It may not be very likely in the fire box but I have replaced many a chimney due to oil burner condensate. You should see what the sulphuric acid does to old lime mortar or even the new cement ones for that matter.

Lou

RePlumbing old hot water system for efficiency

Users who are viewing this thread

Member

DIY Hillbilly

Paid Advertisement

Retired Defense Industry Engineer xxx

Member

Computer Programmer

Master Plumber

Member

Computer Programmer

Retired Defense Industry Engineer xxx

Member

Master Plumber

Master Plumber

DIY Hillbilly

DIY Hillbilly

Computer Programmer

Master Plumber

DIY Hillbilly

Computer Programmer

In the Trades

New Member

Similar threads