Bradford White Combination WH gone bad? Next move?

platinum_overcast

Hello all. First post here, but I've lurked a bit and I'm impressed with the helpful attitude around the site. Hoping for a little bit of insight on what to do with my situation.

Let me apologize in advance for any key details I'm leaving out. I'm new to this world and I probably won't capture everything in this first post. I'll backfill with whatever detail I need to help figure out my next move. I also apologize for any red herrings I'm throwing into the mix. I'm eager to learn.

I've got a 2002 (according to the SN) Bradford White Combination water heater. It's a 75 Gal, 76K BTU input natural gas water heater with an integrated heat exchanger that feeds a radiant in floor heating system. Model number is M2C75T10EN12.

Problem:
I believe that the heat exchanger coil has developed a leak and the potable water is now combined with the radiant heating loop. This seems to be somewhat common on these systems from that era according to a bit of googling.

How I got there:
I decided to check on the expansion tank and see what the air pressure was. Zero. Pretty sure that's not right. Turned off the main, opened a hot water tap at the utility sink and tried to pressurize the tank with a bike pump to something like 12 psi or so. Wouldn't take any pressure, like the Schrader valve was bad. Poked at the valve, the needle moves fine. OK, assume the expansion tank is dead....

Looked at the pressure on the gauge for the radiant zone, read 8psi. Made sense to me...

Closed the tap on the utility sink, opened the main and noticed the pressure gauge on the radiant system swing all the around off the scale on the top side... 60+ psi. Hmm. That doesn't seem right.

Static city water pressure here is 63 psi (I measured it when we built the irrigation system in 2014).

So...

Question 1: Am I right that the heat exchanger coil has been breached in the WH? Or have I missed something?

Question 2: If so, this is obviously bad. I've read about legionella, etc. but this has probably been happening for quite awhile without our knowledge. Nothing will kill us in the next couple weeks, right? It's winter here in Minneapolis and the radiant system is circulating, we're using hot water, etc. Everything is working "fine".

So if we're looking at a new system here, please help me figure out which direction to go.

I'll lay out some house details in the next post.

platinum_overcast

House basics:

Built in 1930

2200sf total.

Unfinished basement (lots of options and space for a replacement system).

First floor is original cast iron radiators with a dedicated boiler. 1100sf. Thermostat on the first floor. Works great.

Second floor is the radiant hot water in floor system (fed by the suspect water heater). Also 1100sf. It's split into 3 loops (zones?) at a manifold on the 2nd floor. No idea which zone runs where, assuming bathroom and two covering the rest of the floor (one large bedroom). Separate thermostat upstairs. This system was installed in 2003 when the PO renovated the upstairs.

2 people live here currently, but would probably size for 4 assuming a family buys the place next.

2 bathrooms, regular size tubs and showers. Dishwasher, washing machine, that's it other than the upstairs radiant system.

platinum_overcast

Other details:

Lots of room in the unfinished basement to rework the utilities in the area near the chimney. Could be multiple heaters, tanks, wall mounted, etc. All of the relevant plumbing is easily accessible.

In general, I'm pretty comfortable with doing the majority of the work myself. May pull in professionals to make some final connections on the gas and water side.

I'm curious to see what makes sense on the efficiency side. We use 200-250 therms/month for the whole house in the winter and drop to about 50 in the summer. I think our 50 therms/month in the summer is higher than average. Wondering if this is due to the relatively gigantic tank, ghost flow, or both? Would a breached heat exchanger coil make this worse?

Please let me know what other information would be helpful.

Ironman

A properly sized combi boiler may be your best option.

Has a heat loss calculation been done to determine the load?

platinum_overcast

Ironman said:

A properly sized combi boiler may be your best option.

Has a heat loss calculation been done to determine the load?

No, but I certainly would be happy to work through one. Any preferred resources to do so?

Rich_49

Did the 76000 BTUh combi perform well in the past ? A heat loss calc would be preferred but 76,000 doing both jobs is quite reasonable . Having all that mass at your disposal for space heat is a good thing and I would recommend staying with that type of strategy to lessen work required to replace .

Some combis with mass are available and made by HTP . All of these would be a substantial improvement over what they would replace and all are modulating units . Phoenix Light duty (http://www.htproducts.com/phoenixldwaterheater.html) is a 76000 BTU unit also that has a low end of 25000 . Although it is not shown in the applications portion of the manual for use with hydronic heating it would certainly perform this way and is not included or drawn that way because the unit is marketed by Warmsource and there would be a conflict is my guess . It's big brother , Phoenix (http://www.htproducts.com/phoenixwaterheater.html) certainly does show this application . There is also the Versa Hydro and Versa Flame . One would pick Versa Flame if high temp for heating is required and DHW is less of a priority and Versa Flame if you can operate space heating below 160* . Versa Hydro is most likely what I would look at in your situation . PHE130-55 . (http://www.htproducts.com/versahydro.html) Low end is 35000 which is lower than you've been operating with and you'll never run out of hot water . All the controls you'd require are built into the unit and it does kick **** .

Check out these heat exchangers , Low if any maintenance . Clean the FPHX every couple years . There is not another unit like this anywhere from anybody .

platinum_overcast

The 76K BTUs have been totally fine for our application.Never come close to running out of hot water and the radiant system upstairs has always kept up with our 64 degree setpoint. It's certainly helped by some convection from the hot water radiators on the ground floor with a 68 degree setpoint (no door on the stairs).

I'm guessing there's a fair amount of overkill. I dug up a PDF of the brochure for the current unit (attached).

Relevant specs (maybe):
Input: 76K BTU/h
CAef: .52
Thermal Efficiency: 82.6
1st Hr: 131 gal
Rec Rate 90F Rise: 85 GPH
Space heating CAafue: 82.4
Max heating capacity: 62K BTU/h

I would bet that max heating capacity is based on running the DHW at something much higher than our setpoint (125-130).

kcopp

How many bathrooms?
Combis are decent for 1 bath or 1 shower at a time.... Beyond that they will struggle.

platinum_overcast

Two bathrooms. Nothing fancy on the shower or bathtub front.