MPO IQ oil boiler too big for house

Lynn29

The installer told us there were adjustments that could be made since our new oil boiler is too big for our 900 sq ft home. But after we called to complain about excessive heat or cold he suggested installing a strap on aquastat. I'm not sure if I need one or not? If we set thermostat to 70 once it reaches that temp and shuts off the temp continues to rise. But if we set temp lower so that the temp will rise to 70 then we have to wait for the heat to kick on. By then chilly. The boiler is throwing great heat, fast. But we can't regulate it. Will the aquastat help? Would turning down the water temp help? Thanks!

Jamie Hall

Need a lot more information here. Make, model, size of boiler? I presume this is hot water heat? What controls -- if any -- are on the boiler now? One zone and thermostat, or more than one? How much radiation (baseboards, radiators?) is connected?

Robert O'Brien

There isn't an oil boiler made that's the right size for 900 sq/ft. But that has no impact on your immediate problem. Need more info

Steamhead

What @Jamie Hall and @Robert O'Brien said. Also need to know if the system is split into different zones.

Outdoor reset might be the way to go here. This can be added to the boiler's IQ control.

STEVEusaPA

I think ODR will only make it worse. Only a buffer, maybe a reverse indirect would help.

Lynn29

Ok, I've gathered more info. We have one zone. Radiator heat. 5 radiators.
Programmable thermostat, though we've been overriding that due to the high temps we're getting. I'll attach some pics. It is piped into the chimney which is clay lined. I took pic of tag on side against wall using a mirror. I apologize, I don't know much About boilers. I'm frustrated with the current situation of not being able to regulate the heat. This is worst when outside temps are milder. I appreciate all of your input. @Steamhead can you explain how/why outdoor reset would help?

SuperTech

Outdoor reset would help by regulating the how hot the water in the boiler and radiatiors is depending on how cold it is outside. That way the boiler only heats up the water to its highest temperature on the coldest days of the year. This will also help save fuel. I think it would help. I also think that primary secondary piping and a mixing system wether it is variable speed injection pumping or possibly a outdoor reset controlled mixing valve would help. It would allow the boiler to circulate heated water for a much longer time at an appropriate temperature for the outdoor conditions. I believe this will improve overall comfort and eliminate short cycling and all the problems associated with that

The installers couldn't be bothered with removing the old equipment? What's that about?

Intplm.

And if I'm not mistaken? Are those wrote copper DWV fittings?

KC_Jones

SuperTech said:

The installers couldn't be bothered with removing the old equipment? What's that about?

I'm pretty sure they piped through the old boiler. Not removing I could maybe understand, but piping through the old boiler, to me is just wrong.

GBart

Looks like a DIY disaster.........looks like the new boiler is piped through the old...........remarkable

STEVEusaPA

Curious as to why @SuperTech & @GBart disagree with me?
ODR with an oversized boiler will result in short cycling with oil, especially with injection mixing. 3-way or 4-way mixing to protect the boiler would be a better way to go.
I do agree it’s a disaster, especially the illegal flue pipe.
Looks like the piped in a 'buffer tank' after all-the old boiler.

JUGHNE

Buffer tank or lame P/S piping??

Would like to see a side view of that expansion tank.

Looks like a get in, get done, get out, get paid and then flip the house?

Lynn29

I got several bids on a new boiler. There were different boiler suggestions. This guy came in cheapest with the mpo. I read up on the mpo and it sounded great. Seemed win, win. We wanted rid of the old coal furnace that we had previously used as secondary heat by burning wood. He talked us into keeping it. It was a quick install and he was gone. When I asked about the excessive temps his answer was to buy a strap on aquastat. I'm at a loss here. Don't have a clue how to proceed. Any suggestions will be appreciated. Dumb it down please. What definitely needs corrected?

Lynn29

@STEVEusaPA ...illegal flu pipe?

JUGHNE

You probably would not want this guy to come back, IMO.
Where are you located? Check the Find a Contractor link above.

BTW, there is already an aquastat on the piping.

Solid_Fuel_Man

His "aquastat" suggestion is bogus. Outdoor reset will improve your temp swings, which are due to the mass you have in those 5 radiators.

Think of those radiators like a heavy cast iron frying pan. You've got some onions to caramelize. If you put the onions in and turn on the burner on high it will take a few minutes for that heavy pan to heat up. Now that everything is hot your onions are sauteing up well. Once they have reached the caramel stage you turn off the burner. Those onions are going to keep cooking and burn due to the heat stored in that pan.

You have two options:

A: Turn the burner off early
B: Turn the burner down once the pan is heated but onions are not cooked yet

Option B is like outdoor reset (ODR) there is a temperature sensor outside which tells the boiler to make the water hotter as it gets colder out. The upside is you have better comfort, the downside is it will short-cycle your boiler. Meaning the burner will turn on and off at shorter intervals instead of running for one long run. However with it piped into the old boiler like it is that may not be as much of an issue.

SuperTech

> @STEVEusaPA said:
> Curious as to why @SuperTech & @GBart disagree with me?
> ODR with an oversized boiler will result in short cycling with oil, especially with injection mixing. 3-way or 4-way mixing to protect the boiler would be a better way to go.
> I do agree it’s a disaster, especially the illegal flue pipe.
> Looks like the piped in a 'buffer tank' after all-the old boiler.

No disrespect intended to you Steve. I'm not saying my opinion is better than yours. I've read countless posts from you here and on HVAC talk, I know you know what you are doing.

I feel as if lower water temperature may help lessen the frequency of the boiler cycles and longer periods of circulation may help improve comfort. Injection pumping as a remedy probably could be done, but I agree the desired results would be easier achieved by usage of a mixing valve.

Let me know why you think it wouldn't work. If I'm wrong I'll gladly admit it if I learn something in the process

I didn't take a long enough look at that piping. I was distracted by the antique boiler and horrible venting. Was it DIY or a handyman special? I hope a pro didn't do that intentionally.

It's sad we have to have these discussions in 2019. So much information is out there saying the number one rule is try to not size the boiler incorrectly for best results.

SuperTech

Hopefully if an ODR is used it will have anti short cycle timer available. But they don't design these things with grossly oversized boilers in my mind as far as I know.

STEVEusaPA

Lynn29 said:

@STEVEusaPA ...illegal flu pipe?

You can’t have gas and heating oil in the same flue pipe. In jurisdictions that allow both in the same chimney, the gas vent pipe (smaller btu) needs to enter the chimney higher than the heating oil flue pipe. The common pipe is of the wrong gauge, but not needed once it’s fixed by removing the water heater flue pipe. Then you can make the flue pipe for the boiler all 5”.

Lynn29

Going to look for a new contractor. I recall the one who installed the mpo gave a very basic quote. No details. I guess I know why now. I really appreciate all of you taking the time to respond.

DZoro

I'm at a loss on how it could possibly work the way it is piped. Other than exactly what the HO is telling us. It is basically heating up the old boiler, shuts down and then gravity heats the home.
I'm sorry but you got taken.
Will have to be re-piped, without the old boiler for it to work properly.
IMO.

nicholas bonham-carter

How did you find the installer-maybe Yelp, or Angie’s list? Was the installation ever inspected?
If he thought at all, maybe his plan was for the old boiler to act like a buffer tank, (sort off??).—NBC

SuperTech

There's no way that was ever inspected. I can't imagine an inspector ever letting that fly.

Lynn29

@nicholas bonham-carter he's local, came well recommended. Sadly, was in and out in a matter of hours and got an attitude when I called with questions. Then suggested aquastat. I was familiar with that because we had one on the old coal boiler. It did what we wanted it to. However, didn't make sense regarding this situation. Oh, and there was No inspection.

Anyone know what an outdoor reset should cost?

GBart

You need way more than an outdoor reset unfortunately.

I have always wondered about these homes we run into with oil heat and gas hot water, I have seen old boilers like that left in but valved off because they can be used as a wood boiler in emergencies.

You need to get a pro in there and possibly the building inspector.

JUGHNE

Was a gas Modcon boiler ever suggested?

DickC

This is so ridiculous, people are getting away with this kind of work. Appears to be an old gravity system (one of the best systems around especially in this case with 5 radiators) and they came in and gaffed this up. ODR will not solve this as the ridiculous piping job heats up the old boiler and that ends up basically running away overheating the home. The "simplest" thing would be to separate the supply and return pipes and connect to the new boiler with flowcheck to prevent gravity circulation. Personally, I'd connect the supply and return piping, remove circulator and wire thermostat to the burner and return it to gravity. These were very comfortable systems with even heat throughout the winter. Limited drawback during spring and summer with lag if the day was warm. They really functioned very much like ODR only putting as much heat in as was needed to heat the house. Boiler water temperature rarely went over 150°. Using a clock thermostat would necessitate adjusting on time to allow for the operation, in most cases the reset was minimal. Usually end up getting messed up by putting a circulator on them. Not sure where you live but someone should notify authorities and put this guy out of business.

Steamhead

DickC said:

Personally, I'd connect the supply and return piping, remove circulator and wire thermostat to the burner and return it to gravity.

Won't work on an MPO- the pipes are too small.

If we know how many square feet of radiation that system has, we can size the circ with this chart, to match the gravity flow rate as closely as possible:

https://heatinghelp.com/systems-help-center/sizing-circulators-for-old-gravity-hot-water-heating-systems/