My fireplace has a heat exchanger connected to my hydronic baseboard system

BCeagle08

This year I purchased a home built in the early 1970s. I discovered that my fireplace has a heat exchanger inside of it where the grate normally is. This heat exchanger is metal tubing with an inlet and and outlet pipe that pass through the floor of the fireplace. The metal tubes get hot when my oil boiler and hydronic baseboard system are operating. I guess this means it is full time plumbed into my baseboard system and the inside of my fireplace is heated whenever my boiler is firing. On the wall near the fireplace there is a switch with a red light. The red light goes on whenever my circulator pump is running. If I turn the switch on when the thermostat is not calling for heat, the red light turns on, the circulator pump on my boiler turns on, but the boiler doesn't fire. The red light appears to be an indicator for whether or not the circulator pump is operating.

I guess this setup is supposed to allow me to heat the water in my hydronic system via the fireplace without the use of my boiler.

Some questions:

1) Is this safe? I have concerns that my wife will start a fire, forget to turn the circulator on, and then I have pressure building up in my system and venting in the basement, or worse, exploding. There is an expansion tank and a pressure relief valve in my system, but it's normal sized for a normal boiler and they don't appear special in any way.

2) What do they even call this type of system? I can't find any info on it on the internet despite my best tries.

3) What sort of safety precautions should I use when building a fire and operating this?

4) Who is more suited to inspect this system - a HVAC/Plumber tech or a chimney inspector?

5) There are two capped pipes in the fireplace that pass through the wall of the fireplace and into the cavity behind the adjacent wall. They are separate from the pipes that come out of the floor of the fireplace to tie into the heating system (water inlet, water return). I don't know what the two capped pipes are for. Does anyone have any idea?

Thanks!

Jamie Hall

People surely did get ingenious. On 5 -- I haven't a clue. However, I'd be very much inclined to find out -- by cracking a cap open a smidge -- whether they have pressure in them or, worse, water. If they do, I'd really try to find out what they are connected to -- such as maybe to the pipes in the fireplace floor. If they aren't connected to anything somewhere odd, they really should be allowed to vent.

On 4. Neither one. The chimney people are really good at masonry and liners and all, but your pipes will baffle them. Unless you find an HVAC guy or gal who can really think outside the box, they won't be much help either.

On 3. And related, 1. If you are reasonably certain that there is, in fact, a direct connection -- no valves including check valves -- from at least one end of those pipes back to the boiler and, therefore, the expansion tank and the pressure relief valve, the worst that can happen that I can see is that the water in those pipes might come to a boil. This will raise the pressure in the system and may raise it enough to open the pressure relief valve -- which would leave you a little low on water (unless you have an automatic feeder) but is just doing what it's supposed to do. There would, however, be no harm to putting a high temperature thermostat right next to the fireplace on the hearth -- you could probably use an aquastat -- wired to turn on the circulator when the fireplace was in use without operator intervention. Perhaps even better, if you can get at the pipes very close to where they are buried in the hearth, would be a low temperature (say 160) aquastat on the pipe on the outlet side to do the same thing. That might have some gently perverse effects on the rest of the system -- the circulator might keep running when you didn't expect it to -- but shouldn't be a problem.

On 2. I don't think there is a name for it. It's not a half bad idea, though, when you think about it.

STEVEusaPA

I had a customer years ago who had the same thing. Worked great but seems dangerous for the some of the reasons @Jamie Hall mentioned.
I also wouldn't want that water constantly circulated through the boiler when the boiler isn't firing. But you're heating the water 'for free' and as long as its not condensing in the heat exchanger I guess it doesn't matter.
It's just some good ole Yankee innovation.

Solid_Fuel_Man

I wonder if it is home-made or fabbed in a local shop.

Leon82

How much heat does a setup like that emit? I guess it's better than just a fire.

The guy at the fireplace store near me said the fireplace is -11% efficient and with a blower it would be 7% efficient.

Zman

I think I would get rid of the switch and install an aquastat at the fireplace. That way it would turn on and off automatically. It is odd that they set it up to heat the stove when it is not running and waste energy up the chimney. It might be worth looking into a solution for that.

Solid_Fuel_Man

Problem with an aquastat is that when the boiler runs it will warm the pipes and trigger the aquastat.

If there is a way to put something in the flue a few feet above the fireplace to detect a fire that would be my approach. Leave it running for a few hours after the flue is "cold". This could be easily do e with a thermocouple and a Honetwell t775 controller.

I'd also install a 3 way zone (bypass) valve to bypass the flow of water when the normal heating boiler is running with no fire.

Steam_Starter

Had one in my fireplace growing up. The one we had was called a HydroHearth. Switched circ and a PRV in the basement piped into the hydro loop. If you didn't turn on the circ when you lit a fire the PRV would blow. Freaked my girlfriend out one night because I forgot to turn it on and the PRV let go in the basement right under us.

Was piped into the loop for the Burnham boiler. Never had a problem with it in the 20+ years we had the house.

BCeagle08

Do you think it's dangerous to have a fire without the circulator running?

Steam_Starter

All depends on if you have a PRV piped into the system. As I mentioned, we had a PRV directly in the basement with a blow-down pipe over a floor drain. We also had the PRV on the boiler but the primary one was under the fireplace in the basement.

I would definitely trace out the system and make sure the circ pump works as well as any PRV's that are piped into the system immediately near the vicinity of the unit are in working order.

If it is directly piped into the boiler then I would not run it without the circ pump operating. A quick Google search for Hydrohearth had a CPSC bulletin issued as the units, if they werent piped with a PRV, posed a hazard.

I have no idea how your system is piped. I can't say safe or not without the system being inspected by a licensed pro.

hot_rod

A pressure relief for sure, but every time it goes off, new fresh, high mineral water goes in behind it.

I would worry about cold fresh water hitting a red hot dry tube, if that were possible?

There were a handful of off the shelf fireplace heaters sold, HydroHearth was common at stove shops years ago. Plenty others in Mothers Earth news Along with thousands of DIYers.

BCeagle08

Thank you for all of your comments. After additional research I believe it is indeed a Hydrohearth system, so thank you for that lead.

I am thinking the best course of action is probably to just have a plumber remove the system. We don't build fires often enough to justify this added complication given its risks. I'll likely have the plumber simply bypass it within the hearth.

STEVEusaPA

Just make sure you leave a pipe open. You wouldn't want to trap any water in there.

hot_rod

BCeagle08 said:

Thank you for all of your comments. After additional research I believe it is indeed a Hydrohearth system, so thank you for that lead.

I am thinking the best course of action is probably to just have a plumber remove the system. We don't build fires often enough to justify this added complication given its risks. I'll likely have the plumber simply bypass it within the hearth.

I'd second that opinion

colinbarry

I've heard of "back boilers" being popular overseas. If the heat exchanger is abandoned I would recommend that it be drilled or rendered useless in a way that a future owner is not able to plug a pipe and cause a possible explosion. A google search on back boilers can show you what happens...

Gordy

Number 5 questionable piping stubs, may have been for an indirect WH, or a dump zone, for when the house reached set point.

Can’t imagine not having a dump zone once set point is reached.