Worth upgrading 13 year old boiler to mod/con with heat pump?

[mattd]

Curious to see what general consensus is. Earlier this year installed a 3 ton Mitsubishi heat pump. Was fantastic for cooling even on hottest days throughout the summer. Going into heating season, curious to see how much I’ll actually need the boiler. Located in southern New England.

Quick info…heat pump rated at 42000 btu (full capacity) at 5*F, 78% capacity at -13*F (very rarely reaches that temp here). COP of 4 at 47*F, COP of 2.0 at 5*F, HSFP of 12.5.

Boiler is a 13 year old Williamson conventional cast iron boiler that was originally oil fired and was converted to gas with a Carlin EZ burner 10 years ago. Measured 82% last year efficiency’s . I averaged about 3.5-4 therms per day last December (wasn’t terribly cold).

House is well insulated and air sealed per energy audit.

My main question is it worth upgrading to a mod/con boiler with the heat pump? Would cost me around 5500$ installing myself. I also should probably replace the water heater as it’s 11 years old on a 9 year tank. It’s atmospheric vented gas fired. So with indirect hot water tank in too probably a tad over 7000$, doing it myself.

I’m leaning toward not really worth it with having the heat pump, and nothing really wrong with the boiler. I could see myself saving the money on gas by just using the heat pump vs upgrading the boiler to save maybe, what, a couple hundred per heating season?

For reference, I pay 0.29$/kWh and a little over 2$ per therm. I also have solar. However due to sun angle and trees in winter I only i get about 150-250 kWH per month from October thru February.

Someone please correct me if I’m wrong. Thanks.

 

[SeaJay]

My motto is generally to not fix what ain't broken.

 

[mattd]

I guess the other part of my question is really will I even need the boiler at all, and cost of operation between the two as it is now.

 

[Egg_Head]

How long do you plan on being in that home?

 

[mattd]

How long do you plan on being in that home?

At this point, probably life. I’m 38.

 

[Egg_Head]

Are you married? B/c I thought the same thing in the last home I had...

 

[LazyDog]

Some of those newer boilers required a lot more maintenance and service calls.

As a trial install a modern system but leave the old one in place, similar to 2 water heater on series.

I am willing to bet you, the saving are minimal. How many zones do you on the system???

 

[mattd]

Are you married? B/c I thought the same thing in the last home I had...

Yes.

 

[mattd]

Some of those newer boilers required a lot more maintenance and service calls.

As a trial install a modern system but leave the old one in place, similar to 2 water heater on series.

I am willing to bet you, the saving are minimal. How many zones do you on the system???

2 zone, would add a third for indirect hot water heater. I am capable of doing all needed maintenance. If I don’t change the boiler I’ll just replace the existing water heater.

I agree that I am leaning toward the savings would be minimal, but I wasn’t sure HOW minimal, especially seeing I may not NEED it at all this winter. And whether it’d be more efficient for heating hot water with an indirect tank.

 

[Delta]

That's actually what I plan on doing with my house. My heating is an oil boiler and have a central AC unit. AC unit is an old R22 unit that is rusting out and when it finally does crap out I'm replacing it with a heat pump/AC. However, I'm keeping the oil boiler to use as back-up heat when it gets really cold.

 

[LazyDog]

2 zone, would add a third for indirect hot water heater. I am capable of doing all needed maintenance.

You can break up each zone w/ valves and you might achieved the same savings as a modern system.

In my friends house one pump system got 6 zone valves and each zone is control by a thermostat. His saving where nice because at night he lower the set point from those rooms that where not been used. Just an idea

 

[mattd]

You can break up each zone w/ valves and you might achieved the same savings as a modern system.

In my friends house one pump system got 6 zone valves and each zone is control by a thermostat. His saving where nice because at night he lower the set point from those rooms that where not been used. Just an idea

I have zone valves now with thermostats for each zone. I was going to switch to circulator controlled zones if I replace the boiler and control everything including DHW with a Taco sr503-exp-4

Bottom line is looking for lowest long term cost overall. The heat pump is the only thing I’m not sure about handing 100% of heating needs with balancing cost of operation

Boiler set up will look almost exactly like this if I change set ups.

 

[TCL]

That new setup looks like trouble just waiting to happen.
That old unit looks pretty stout and simple. I wouldn't change a thing if it works good.

 

[Cujet]

The math really is not all that hard to perform. However, we don't have enough information to make a fully informed calculation. Do an honest evaluation and post the results.

My gut reaction is that it is not worth it to upgrade to a modern system. Despite your system efficiency being on the slightly low side. Achieving a combustion based system efficiency over 90% really does require a combustion air source, other than the house itself. Air exchange, is both desired for health, and detrimental for efficiency. If you were to add a dedicated "combustion air" source (not sure if possible in your case) efficiency would go up markedly.

When one has a COP below 3, the heating system is using more energy (as consumed at the power plant) than if fuel was burned to create heat. So, if this matters to you, burn fuel when temps are low.

Off topic: I always thought a Combined Heat and Power system, (that runs a heat pump) would be an interesting experiment. A 44% TE genset, with the heat being used from the cooling system and exhaust/catalyst (cat makes heat) and powering a heat pump. Any excess electrical power used to power the house.

 

[mattd]

The math really is not all that hard to perform. However, we don't have enough information to make a fully informed calculation. Do an honest evaluation and post the results.

My gut reaction is that it is not worth it to upgrade to a modern system. Despite your system efficiency being on the slightly low side. Achieving a combustion based system efficiency over 90% really does require a combustion air source, other than the house itself. Air exchange, is both desired for health, and detrimental for efficiency. If you were to add a dedicated "combustion air" source (not sure if possible in your case) efficiency would go up markedly.

When one has a COP below 3, the heating system is using more energy (as consumed at the power plant) than if fuel was burned to create heat. So, if this matters to you, burn fuel when temps are low.

Off topic: I always thought a Combined Heat and Power system, (that runs a heat pump) would be an interesting experiment. A 44% TE genset, with the heat being used from the cooling system and exhaust/catalyst (cat makes heat) and powering a heat pump. Any excess electrical power used to power the house.

With a COP of 2 it’s giving you 2 units of energy output for every one energy of consumption. Something with a COP of less than 1 means it’s consuming more energy it’s producing. Energy star rated heat pumps have a COP greater than 1.75 and HSPF of 11. Am I wrong seeing that the boiler efficiency of 82% meaning that COP is 0.82? I guess it comes down to base fuel cost/consumption.

Edit: Just dug some math up..so figured out my boiler will cost about 0.09$ per kWh at 82% efficiency to operate regardless of temp. My heat pump will cost about 0.065$ per kWh to operate at 47 degrees and 0.145$ per kWh at 5 degrees. I just don’t know what the heat pumps ratings are at 32 degrees. It’s not published. Only at 17 degrees which is COP of 2.1 and at 5 degrees it’s 2.0. This is all based of the current electric and gas rates I pay.

 

[mattd]

That new setup looks like trouble just waiting to happen.
That old unit looks pretty stout and simple. I wouldn't change a thing if it works good.

You’re right. It doesn’t get any simpler than what I have. I was just looking for increased efficiency but trying to determine if the cost is worth the money. So far it does not seem like it is a good enough return on the investment, which is what I was more or less thinking from the get go. But wanted some other opinions.

 

[eljefino]

If you shut it down will the far corners of the pipes freeze in the walls somewhere?

I have a homemade gizmo that calls for heat in the main zone for 60 seconds every 60 minutes when it's below 35'F outside, just to keep things from freezing, and to get a little heat to the far corners of the house.

The main room is heated by a heat pump or wood stove usually.

You should keep this boiler around for emergencies and power outages. It will likely take much less electricity to run compared to the heat pump, so a small generator will do.

 

[mattd]

If you shut it down will the far corners of the pipes freeze in the walls somewhere?

I have a homemade gizmo that calls for heat in the main zone for 60 seconds every 60 minutes when it's below 35'F outside, just to keep things from freezing, and to get a little heat to the far corners of the house.

The main room is heated by a heat pump or wood stove usually.

You should keep this boiler around for emergencies and power outages. It will likely take much less electricity to run compared to the heat pump, so a small generator will do.

I would probably switch it to emergency circulation/freeze protection below freezing. I had that thought also.

I’d never get rid of it just because. I will keep it hooked up if I don’t go to a condensing boiler. The frequency of use will be much less than before though.

 

[JHZR2]

I love my mod/con boiler and indirect water. Efficient and excellent. But if you’re not having issues, I would say it depends upon how efficient/leaky your house is.

 

[Snagglefoot]

Curious to see what general consensus is. Earlier this year installed a 3 ton Mitsubishi heat pump. Was fantastic for cooling even on hottest days throughout the summer. Going into heating season, curious to see how much I’ll actually need the boiler. Located in southern New England.

Quick info…heat pump rated at 42000 btu (full capacity) at 5*F, 78% capacity at -13*F (very rarely reaches that temp here). COP of 4 at 47*F, COP of 2.0 at 5*F, HSFP of 12.5.

Boiler is a 13 year old Williamson conventional cast iron boiler that was originally oil fired and was converted to gas with a Carlin EZ burner 10 years ago. Measured 82% last year efficiency’s . I averaged about 3.5-4 therms per day last December (wasn’t terribly cold).

House is well insulated and air sealed per energy audit.

My main question is it worth upgrading to a mod/con boiler with the heat pump? Would cost me around 5500$ installing myself. I also should probably replace the water heater as it’s 11 years old on a 9 year tank. It’s atmospheric vented gas fired. So with indirect hot water tank in too probably a tad over 7000$, doing it myself.

I’m leaning toward not really worth it with having the heat pump, and nothing really wrong with the boiler. I could see myself saving the money on gas by just using the heat pump vs upgrading the boiler to save maybe, what, a couple hundred per heating season?

For reference, I pay 0.29$/kWh and a little over 2$ per therm. I also have solar. However due to sun angle and trees in winter I only i get about 150-250 kWH per month from October thru February.

Someone please correct me if I’m wrong. Thanks.

Can you pick a city and I’ll call up a Weatherspark graph.