To replace or not replace 30 year old Burnham boiler in 2000 ft2 slab ranch home?

Radiantfan

Thank you in advance for helping me to answer this question - I'm happy to have found this forum. We live in a 2000 ft2 slab ranch home built in 1966. It has radiant heat in the slab (which we love) powered by a natural gas fired 30 yr old Burnham boiler. We are in MA and there is currently a rebate of $2950 if we replace with a 95% efficient boiler. The requirements are the existing boiler has to be at least 30 years old and still working. Our boiler meets these requirements.

I've had a couple of quotes from local plumbers and if the rebate didn't exist, I would likely just keep running the old Burnham. However, the rebate makes it semi-affordable. One company quoted a KHB199N Lockinvar Knight Boiler and the other quoted a Viessmann Vitodens 100-W-B1HA-35. We already have a Rinnai on demand hot water system so the boiler only needs to heat the radiant. My monthly gas bill is on an equal installment and runs $140 per month. I'm wondering if A) Should I replace the Burnham with a high efficiency unit while the rebate is in effect and if yes Which boiler is the better unit or does brand really make a difference?

We plan to live in this home for the next 20 years.

Radiantfan

Also, looks like the Lockinvar is 199K btu while the Vitodens is 100K btu? Why did one company spec twice the output?

JUGHNE

What size is your existing boiler?

HVACNUT

> @JUGHNE said:
> What size is your existing boiler?

That has absolutely no bearing on what size the new boiler should be.

Was a heat loss calculation done? Probably not. That's the first, and very important step.
Without the need for domestic hot water, even 100K BTU's is probably too much but the turn down ratio and outdoor reset will match the load if installed and programmed properly.

GroundUp

I can only guess the Lochinvar guy hasn't a clue what he's doing and "that's what we always put in" is his crutch. I'd lose his number immediately. In your climate, assuming the home is of reasonable insulation value and tightness, odds are very slim the heat load is more than 60,000 at design and probably closer to 40,000 but somebody needs to do a proper heat loss calculation to determine the actual BTU needed to heat your home. There's a chance one or the other looked at your existing boiler and decided to quote another of the same size, but that is not the right way to go about it. Both Lochinvar and Veissmann make quality boilers, but finding a contractor that knows their stuff is going to be a more important step than the boiler itself. To answer the main question though, for that amount of money I would not hesitate for 1 second to replace the 30 yr old Burnham in lieu of something 15% more efficient

Radiantfan

HVACNUT said:

> @JUGHNE said:

> What size is your existing boiler?



That has absolutely no bearing on what size the new boiler should be.



Was a heat loss calculation done? Probably not. That's the first, and very important step.

Without the need for domestic hot water, even 100K BTU's is probably too much but the turn down ratio and outdoor reset will match the load if installed and programmed properly.

I don't know if a heat loss calculation was done - I didn't ask and they never said. I noticed that the part number for the Viessmann ends in a 35, which may indicate 35k btu? The Viessmann website specs 21 - 125 MBH for this unit, but does not specify btu and I don't know how MBH converts to BTU?

Radiantfan

GroundUp said:

I can only guess the Lochinvar guy hasn't a clue what he's doing and "that's what we always put in" is his crutch. I'd lose his number immediately. In your climate, assuming the home is of reasonable insulation value and tightness, odds are very slim the heat load is more than 60,000 at design and probably closer to 40,000 but somebody needs to do a proper heat loss calculation to determine the actual BTU needed to heat your home. There's a chance one or the other looked at your existing boiler and decided to quote another of the same size, but that is not the right way to go about it. Both Lochinvar and Veissmann make quality boilers, but finding a contractor that knows their stuff is going to be a more important step than the boiler itself. To answer the main question though, for that amount of money I would not hesitate for 1 second to replace the 30 yr old Burnham in lieu of something 15% more efficient

I believe you are correct regarding the Lochinvar guy - I don't have a lot of confidence in him, and now so even less. I've used the company that quoted the Veissmann before and they do quality work. I believe the unit they quoted is actually 35k btu (going by the part number), but I will ask them.

Thanks for answering the main question - I'm thinking now's the time to pull the trigger while I'm eligible for the rebate. Do you have any idea what I could expect to save per month on my $140 gas bill? We've renovated the whole house over the last 15 years with new insulation, windows, doors, siding, etc and reduced our monthly gas bill from $280 to $140. How much would you expect a high efficiency boiler to reduce our gas bill?

JUGHNE

IMO, the size of your existing boiler does matter.
Whatever it is you will need something smaller.
Do you recall how constant the burner ran on the coldest days of the year? Not the pumps but the fire itself.
If either quote indicated a larger size then they are both out of the race. A new Modcon boiler will deliver at least 10% more heat for input than your old. With low temp radiant floor then 15% more for sure.

Yes, a heat loss should be done. But do you know what was installed for perimeter underground insulation?
Buildings of the 1960's seldom had little if any foundation insulation. This would be a major heat loss factor for your calculations.
Does the snow melt away from your foundation?
It has been said that radiant floor houses built in the 50's would have plants growing near the house in cold weather.

Has your gas billing always been on the equal monthly payments?

And now that I have "poked the bears" it would be interesting to know the size of the existing boiler.

Radiantfan

JUGHNE said:

IMO, the size of your existing boiler does matter.
Whatever it is you will need something smaller.
Do you recall how constant the burner ran on the coldest days of the year? Not the pumps but the fire itself.
If either quote indicated a larger size then they are both out of the race. A new Modcon boiler will deliver at least 10% more heat for input than your old. With low temp radiant floor then 15% more for sure.

Yes, a heat loss should be done. But do you know what was installed for perimeter underground insulation?
Buildings of the 1960's seldom had little if any foundation insulation. This would be a major heat loss factor for your calculations.
Does the snow melt away from your foundation?
It has been said that radiant floor houses built in the 50's would have plants growing near the house in cold weather.

Has your gas billing always been on the equal monthly payments?

And now that I have "poked the bears" it would be interesting to know the size of the existing boiler.

I used a heat loss calculator and I'm coming up with 50K BTU for a 60 deg temp difference. 56K BTU for 70 deg, 62K BTU for 80 deg. The snow does not melt away from my foundation, but I doubt there is any perimeter underground insulation.

On the gas billing question, not always, but for the last 10 years it's been on balanced billing. When we moved in 15 years ago, our winter months gas bill was as high as $400 to $600 per month so we moved to balanced billing which was still very high at $280/month equal installments. Additional attic and wall Insulation, new doors & windows, hardie plank siding, and Rinnai on demand hot water dropped it to $140.

Radiantfan

I contacted the plumbing company who quoted the Veissmann. It's a 125k BTU unit. Owner said "it's plenty big enough for your house". I asked him if he knew what my Burnham boiler is and he said no. He said it's 30 years old so probably only running at 70% efficiency compared to the 95% efficiency of the Veissmann. Plus the fact that the Vmann will modulate boiler temp based on outside temp rather than heating to 180deg all the time like the old Burnham. He did not respond to my question if he did a heat loss calc so my assumption is he did not.

Jamie Hall

OK. You did a heat loss for 70 degrees inside, and came up with 56K. Yo were quoted a boiler with a rating of 125K. Two and a half times as big as you need. Something wrong there? Just maybe?

Somebody needs to try again...

Radiantfan

Jamie Hall said:

OK. You did a heat loss for 70 degrees inside, and came up with 56K. Yo were quoted a boiler with a rating of 125K. Two and a half times as big as you need. Something wrong there? Just maybe?

Somebody needs to try again...

Well, I used a quick online heat loss calculator guesstimating the wall ft2 and window ft2 so I wouldn't put a lot of stock in that 56K number.

GroundUp

Those heat loss numbers were at 60,70,80 degree differential from outdoor temp or are those the actual indoor temps using your local design temp? For example, here in my part of MN, design temp is -20F so if I wanted it 70 degrees inside would make a 90 degree differential at design. The reality is that it does reach -40F for about a week every year so that differential is 110 worst case scenario. Slant Fin has a free heat loss calculator online that you can input all your values and come up with a more accurate number specific to your house. Considering the envelope upgrades, I would have a hard time believing your heat loss to be over 60k at design. 30 BTU per sq ft is pretty high unless it's a drafty home or has a ton of glass. A proper heat loss calculation is going to be step one here. As for the efficiency, a condensing boiler is likely going to bring it up 15-20% with radiant so if your bill is 140 now, maybe figure on saving 20-30 bucks a month

Radiantfan

GroundUp said:

Those heat loss numbers were at 60,70,80 degree differential from outdoor temp or are those the actual indoor temps using your local design temp? For example, here in my part of MN, design temp is -20F so if I wanted it 70 degrees inside would make a 90 degree differential at design. The reality is that it does reach -40F for about a week every year so that differential is 110 worst case scenario. Slant Fin has a free heat loss calculator online that you can input all your values and come up with a more accurate number specific to your house. Considering the envelope upgrades, I would have a hard time believing your heat loss to be over 60k at design. 30 BTU per sq ft is pretty high unless it's a drafty home or has a ton of glass. A proper heat loss calculation is going to be step one here. As for the efficiency, a condensing boiler is likely going to bring it up 15-20% with radiant so if your bill is 140 now, maybe figure on saving 20-30 bucks a month

Thanks - those numbers are differential from outdoor temp. I will check out the calculator on Slant Fin to get a more accurate number. If I understand you correctly, the 95% efficient boiler btu output should be the heat loss / .95?

The home is very tight with normal size windows plus two sliders and one bay window. $20 - $30/month savings is good, but the payback will be about 20 years at $360/yr based on the installed boiler cost. Makes it a bit tough to justify the investment, but we don't know how much longer the Burnham will last which is why I posted here in the first place lol!

GroundUp

That's correct. Considering the rebate or whatever, plus the payback you just mentioned, you might consider another contractor. If you figure you might have to replace the failed Burnham in 5 years and miss the rebate, what's your payback then? I wouldn't hesitate for 1 second to upgrade

mikeg2015

Is those one of those Burnhams with the cast iron burners? I saw one of those that was 45 years old a few months ago. Not a single leak, burners had a nice, even steady blue flame like they were brand new. I think that unit could last 60 years if kept sealed, never opened up and drained.

It’s probably still 80% combustion efficiency with a flue damper, less the losses from the pilot in off season.... unless it has draft issues and there’s buildup on the heat exchanger.


What temperature water do you need to maintain space temp on a design day? Actual boiler output depends on return water and firing rate. At full firing rate, most condensing boilers are rarely over 90% if return water is over 110F. Once return water is over 130F, you’r down to around 88-89% barely condensing). At 150F return water it’s 86-87%.

Just like mini split systems, the dirty secret is that at full load and higher temps, they aren’t that efficient. Fortunately they run most of hte time at part load nad are typically oversized a little too.

mikeg2015

Had a Lochinvar FTXL at a college I was working at. At 120F return water there was little condensate coming out, picked up at 100F and at 85F it was pouring out... all at similar firing rates.