Standard vs High Efficiency boiler

northernsoul

Hi there

Starting to plan to replace our current gas boiler (slant/fin 18 year old standard gas boiler) and if we should go with another standard type (and replace the current chimney flue/vent pipe at the same time) or go for a high efficiency one with the direct vent through the wall .

Our house is 1940s double brick with no wall insulation and we still have the original cast iron rads and pipes - so not sure if it's worth the cost and install time for a high efficiency boiler.

Thoughts?

NY_Rob

A good first step would be to use the slant/fin app to perform a heatloss analysis of your home.
http://www.slantfin.com/slantfin-heat-loss-calculator/

That will give you a ballpark idea of the BTU output you require for whatever type of boiler you decide to go with. Don't accept boiler sizing from hack contractors based on "what you have now" who are too lazy to do their homework. By sizing based on what you have now- it's pretty much guaranteed you'll oversize by at least 50% but maybe even 2x or 3x what you actually need.

With that in mind, if the numbers line up... mod-con boilers love cast iron radiators. They heat and cool slowly which is ideal for a mod-con boiler to achieve maximum efficiency and long life.

northernsoul

Thanks - I'll give that app a try. Are mod con boilers more costly than traditional hydronic boilers?

John Mills_5

A good mod-con would be quite a bit more plus the extra pump(s) and piping for primary-secondary.

What's the radiation? Fin tube baseboard runs fairly warm and can have the condensing boiler above the condensing temp quite a bit of the time, especially if you do setbacks. That means you have a very pricey 85% boiler. If you have in-floor radiation or the old cast iron radiators, mod-cons love the cooler water temps.

northernsoul

They are the original cast iron rads.

SuperJ

The more gas you use the more a high efficiency boiler makes sense. Many systems can make use of a condensing boiler if a little thought and effort is put in.

Look at this Coffee with Caleffi, at about 37minutes in.

https://youtu.be/6mNECDHgDrg?t=37m

Gordy

Is there anything wrong with your 18 year young boiler? Could see another 12 years if it has been properly maintained.

Is it over sized?

Does present system utilize outdoor reset?

As been said a heatloss room by room should be done along with an emitter survey to determine if lower average water temperatures can be used. The lower water temps if possible brings the efficiency of a mod con up if chosen.

The EDR survey determines how much output the radiantion has for the heatloss of the room. If the radiation is oversized then lower Water temps can be used.

northernsoul

> @Gordy said:
> Is there anything wrong with your 18 year young boiler? Could see another 12 years if it has been properly maintained.
>
> Is it over sized?
>
> Does present system utilize outdoor reset?
>
> As been said a heatloss room by room should be done along with an emitter survey to determine if lower average water temperatures can be used. The lower water temps if possible brings the efficiency of a mod con up if chosen.
>
> The EDR survey determines how much output the radiantion has for the heatloss of the room. If the radiation is oversized then lower Water temps can be used.

We just bought the house llast year so I am not sure how well it's been maintained since installed other than the inspections for CO2 etc.

I am not sure what an outdoor reset is?

I am not convinced it's presently working at full efficiency it could be - it doesnt seem to go higher than 12 PSI, the temp is usually running only about 140 and not all the 2nd floor rads heat all the way accross.

At the very least it prob needs a good cleaning etc.

the_donut

Outdoor reset adjusts supply water temperature based on outdoor temp. You don’t need 140* water when it’s 55*.

Pressure should stay pretty consistent from compression tank.

What type of radiators? Some require throttling supply to allow water to slow down and heat to rise. Also you may look at bleeding radiators.

northernsoul

> @the_donut said:
> Outdoor reset adjusts supply water temperature based on outdoor temp. You don’t need 140* water when it’s 55*.
>
> Pressure should stay pretty consistent from compression tank.
>
> What type of radiators? Some require throttling supply to allow water to slow down and heat to rise. Also you may look at bleeding radiators.

Hmm I don't think it has an outdoor reset based on the age of the boiler and Idokt see any wires leading outside.

The rads are cast iron.

The expansion tank is an old long metal one strapped between the joists.

I had the rad serviced recently due to ignition problems and he replaced the pilot sensor and suggested I replace the auto feed valve as the adjuster screw wasn't turning properly.

EBEBRATT-Ed

Step #1 do the Slant Fin heat loss. You won't know if your old boiler is oversized or not
Step #2 if you second floor radiators don't heat they likely won't heat with a new boiler either. That problem needs to be fixed.
Step #3 If the size if you old boiler is reasonable, have it cleaned and do a combustion efficiency test.

Then you will have the information to make a decision.

You need a qualified contractor

Jamie Hall

12 psi is enough for a two story house (not more than 25 feet vertical from the pressure gauge to the top of the highest radiator). It shouldn't vary much -- a little higher when the boiler is running, but not that much.

The second floor radiators which don't heat all the way across may need to have air bled out of them -- that's the simplest possibility anyway. Not hard to do; there should be a bleeder -- a little spigot sort of thing -- on one end of the radiator at the top. If you're lucky it has a knob. Otherwise, they take a particular wrench -- which should be somewhere near the boiler, but I'll bet it's long since mislaid. Anyway, having made sure you do have 12 psi, bleeding is simply a matter of opening that little valve until water comes out. Then, of course, closing it again...

And rechecking the water pressure. Even if the boiler has an automatic feed, they don't always behave properly.

140 is a little cool for the return temperature for a non-condensing boiler -- which, at 18, yours surely is. There may be a control on the pipe from the boiler (the hot pipe) which sets the temperature at which the boiler runs. It's called an aquastat, and you should check and see what it's set at.

In any event, if you haven't done so, it would probably be worth the money to get a really competent heating professional in to look over the system and controls, bleed the radiators if need be, and clean and adjust the burner on the boiler. If you don't have one, check "Find a Contractor" on this site (it sometimes works best if you look by state, rather than zip code) -- or just tell us where you are and we may be able to recommend someone.

northernsoul

> @Jamie Hall said:
> 12 psi is enough for a two story house (not more than 25 feet vertical from the pressure gauge to the top of the highest radiator). It shouldn't vary much -- a little higher when the boiler is running, but not that much.
>
> The second floor radiators which don't heat all the way across may need to have air bled out of them -- that's the simplest possibility anyway. Not hard to do; there should be a bleeder -- a little spigot sort of thing -- on one end of the radiator at the top. If you're lucky it has a knob. Otherwise, they take a particular wrench -- which should be somewhere near the boiler, but I'll bet it's long since mislaid. Anyway, having made sure you do have 12 psi, bleeding is simply a matter of opening that little valve until water comes out. Then, of course, closing it again...
>
> And rechecking the water pressure. Even if the boiler has an automatic feed, they don't always behave properly.
>
> 140 is a little cool for the return temperature for a non-condensing boiler -- which, at 18, yours surely is. There may be a control on the pipe from the boiler (the hot pipe) which sets the temperature at which the boiler runs. It's called an aquastat, and you should check and see what it's set at.
>
> In any event, if you haven't done so, it would probably be worth the money to get a really competent heating professional in to look over the system and controls, bleed the radiators if need be, and clean and adjust the burner on the boiler. If you don't have one, check "Find a Contractor" on this site (it sometimes works best if you look by state, rather than zip code) -- or just tell us where you are and we may be able to recommend someone.

Thank you!
They are the original American Radiator Corto Rads from the 1930s.
I know we bled almost all the upstairs rads in the fall until water came out, and the one we couldn't get to bleed (nothing came out of spigot) is the one that heats the least.

I don't see any aquastat on the pipes or boiler. Is this something a technician could adjust ? I didn't know the temp gauge was return water temp - always thought it was the outgoing temp.

I have a good HVAC service person I will get back in to clean and test everything

northernsoul

> @EBEBRATT-Ed said:
> Step #1 do the Slant Fin heat loss. You won't know if your old boiler is oversized or not
> Step #2 if you second floor radiators don't heat they likely won't heat with a new boiler either. That problem needs to be fixed.
> Step #3 If the size if you old boiler is reasonable, have it cleaned and do a combustion efficiency test.
>
> Then you will have the information to make a decision.
>
> You need a qualified contractor

Thank you - I thought wrongly that the poor radiant heat in the upstairs was from the boiler not putting out enough pressure to fill the whole rad

D107

HO here; just keep in mind if you install another standard boiler, most likely the newer codes will require you put in a new metal chimney liner, which will add a huge percentage of your costs. If you already have a metal liner, codes and boiler specs will determine if you can keep it.

northernsoul

> @David107 said:
> HO here; just keep in mind if you install another standard boiler, most likely the newer codes will require you put in a new metal chimney liner, which will add a huge percentage of your costs.

I didn't realise that replacing the metal vent pipe and liner would be that much - thanks

SuperTech

I wouldn't want to spend the money on a new boiler unless the one you have isn't repairable. For a fraction of the cost you could update/upgrade your current boiler.

Based on what you have described I would consider installing an outdoor reset control, new diaphragm expansion tank and an a Honeywell Y8610U intermittent pilot retrofit kit to eliminate the standing pilot. Another thing to consider would be installation of thermostatic radiator valves, these will greatly improve your ability to control the temperature in each room and balance the system.

If you post some pictures of your equipment and near boiler piping I will probably be able to suggest some other upgrades that will help improve reliability and efficiency. If you take care of the boiler that you have it could last a long time. 18 years is towards the end of the life expectancy for a forced air system, but for a good cast iron boiler that's nothing. I would also consider the fact that a condensing boiler doesn't have nearly as long of a life expectancy.

northernsoul

> @SuperTech said:
> I wouldn't want to spend the money on a new boiler unless the one you have isn't repairable. For a fraction of the cost you could update/upgrade your current boiler.
>
> Based on what you have described I would consider installing an outdoor reset control, new diaphragm expansion tank and an a Honeywell Y8610U intermittent pilot retrofit kit to eliminate the standing pilot. Another thing to consider would be installation of thermostatic radiator valves, these will greatly improve your ability to control the temperature in each room and balance the system.
>
> If you post some pictures of your equipment and near boiler piping I will probably be able to suggest some other upgrades that will help improve reliability and efficiency. If you take care of the boiler that you have it could last a long time. 18 years is towards the end of the life expectancy for a forced air system, but for a good cast iron boiler that's nothing. I would also consider the fact that a condensing boiler doesn't have nearly as long of a life expectancy.
>

Here are a few pics - thanks!

SuperTech

I would get rid of the flue damper, they tend to fail often and don't do much to help efficiency. Reliability is more important than efficiency. It also might be a good idea to consider a variable speed circulator pump especially if you have zoning. Also a microbubble resorber air eliminator is a great addition to any boiler.

northernsoul

> @SuperTech said:
> I would get rid of the flue damper, they tend to fail often and don't do much to help efficiency. Reliability is more important than efficiency. It also might be a good idea to consider a variable speed circulator pump especially if you have zoning. Also a microbubble resorber air eliminator is a great addition to any boiler.

Thanks!!!- we don't have zoning- still the original piping and corto rads !

northernsoul

> @SuperTech said:
> I would get rid of the flue damper, they tend to fail often and don't do much to help efficiency. Reliability is more important than efficiency. It also might be a good idea to consider a variable speed circulator pump especially if you have zoning. Also a microbubble resorber air eliminator is a great addition to any boiler.

One other question - is the metal box on the right lower side the aquastat?

It's a slant fin model galaxy GG100HXPED

Thanks

Gordy

It’s a low water cut off. It insures the system has sufficient water so the boiler will not fire with out water in it. Safety feature all boilers should have.

Gordy

I wouldn’t get rid of the flue damper. Unless it fails. May never fail. Actually haven’t seen that many issues with them.

Gordy

I say add an air removal device, and leave it run. Use your extra time to research, save money, and have a plan for the future of your system. Think about how long you plan on living there also.

Mod/con home run Rads to manifolds with trvs. Is a start.

In 12 years who knows where hydronics, and heating boiler technology may be.


If fuel prices become the thorn in your side then that could be a time to upgrade.

northernsoul

> @Gordy said:
> It’s a low water cut off. It insures the system has sufficient water so the boiler will not fire with out water in it. Safety feature all boilers should have.
>
>

> @Gordy said:
> It’s a low water cut off. It insures the system has sufficient water so the boiler will not fire with out water in it. Safety feature all boilers should have.
>
>
Sorry I meant the silver metal box in left bottom of the 1st picture. Wasn't sure if that was just the power line or an aquastst

SuperTech

That's just an electrical junction box. I didn't notice an aquastat in any of the pictures, it might be inside the boiler. The wires from the flue damper usually go to the aquastat.

What do have to make domestic hot water?

northernsoul

> @SuperTech said:
> That's just an electrical junction box. I didn't notice an aquastat in any of the pictures, it might be inside the boiler. The wires from the flue damper usually go to the aquastat.
>
> What do have to make domestic hot water?

Separate gas fired hot water tank